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GeeCON Prague 2014 - Metaprogramming with Groovy

Iván López Martín
Iván López Martín

The document discusses metaprogramming in Groovy, emphasizing its dynamic nature and runtime capabilities through the meta-object protocol (MOP). It provides examples of how to implement property and method interception using interfaces like GroovyObject and GroovyInterceptable, as well as how to modify metaclasses to inject methods and properties. Overall, the document illustrates various techniques to extend class functionalities at runtime.

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Iván López @ilopmar METAPROGRAMMING WITH GROOVY
Hello! I am Iván López @ilopmar
Groovy is dynamic ▷ “Delay” to runtime some decisions ▷ Add properties/behaviours in runtime ▷ Wide range of applicability
What is metaprogramming?
“ Metaprogramming is the writing of computer programs that write or manipulate other programs (or themselves) as their data. - Wikipedia
1. Runtime metaprogramming
Runtime metaprogramming ▷ Groovy provides this through Meta-Object Protocol (MOP) ▷ Use MOP to: – Invoke methods dynamically – Synthesize classes and methods on the fly
What is the Meta Object Protocol? Groovy Groovy Java Java MOP
Intercepting methods using MOP
Groovy Interceptable ▷ GroovyObject interface ▷ Implement GroovyInterceptable to hook into the execution public interface GroovyObject { Object invokeMethod(String name, Object args) Object getProperty(String propertyName) void setProperty(String propertyName, Object newValue) MetaClass getMetaClass() void setMetaClass(MetaClass metaClass) }
GroovyInterceptable example class Person implements GroovyInterceptable { String name Integer age public Object getProperty(String propertyName) { println "Getting property '${propertyName}'" return this.@"${propertyName}" } public void setProperty(String propertyName, Object newValue) { println "Setting property '${propertyName}' with value '${newValue}'" this.@"${propertyName}" = newValue } // Execution Setting property 'name' with value 'Iván' Setting property 'age' with value '34' Getting property 'name' Getting property 'age' Hello Iván, you're 34 } def person = new Person() person.name = "Iván" person.age = 34 println "Hello ${person.name}, you're ${person.age}"
GroovyInterceptable example class Person implements GroovyInterceptable { String name Integer age public Object getProperty(String propertyName) { println "Getting property '${propertyName}'" return this.@"${propertyName}" } public void setProperty(String propertyName, Object newValue) { println "Setting property '${propertyName}' with value '${newValue}'" this.@"${propertyName}" = newValue } // Execution Setting property 'name' with value 'Iván' Setting property 'age' with value '34' Getting property 'name' Getting property 'age' Hello Iván, you're 34 } def person = new Person() person.name = "Iván" person.age = 34 println "Hello ${person.name}, you're ${person.age}"
GroovyInterceptable example class Person implements GroovyInterceptable { String name Integer age public Object getProperty(String propertyName) { println "Getting property '${propertyName}'" return this.@"${propertyName}" } public void setProperty(String propertyName, Object newValue) { println "Setting property '${propertyName}' with value '${newValue}'" this.@"${propertyName}" = newValue } // Execution Setting property 'name' with value 'Iván' Setting property 'age' with value '34' Getting property 'name' Getting property 'age' Hello Iván, you're 34 } def person = new Person() person.name = "Iván" person.age = 34 println "Hello ${person.name}, you're ${person.age}"
GroovyInterceptable example class Person implements GroovyInterceptable { String name Integer age public Object getProperty(String propertyName) { println "Getting property '${propertyName}'" return this.@"${propertyName}" } public void setProperty(String propertyName, Object newValue) { println "Setting property '${propertyName}' with value '${newValue}'" this.@"${propertyName}" = newValue } // Execution Setting property 'name' with value 'Iván' Setting property 'age' with value '34' Getting property 'name' Getting property 'age' Hello Iván, you're 34 } def person = new Person() person.name = "Iván" person.age = 34 println "Hello ${person.name}, you're ${person.age}"
GroovyInterceptable example class Person implements GroovyInterceptable { String name Integer age public Object getProperty(String propertyName) { println "Getting property '${propertyName}'" return this.@"${propertyName}" } public void setProperty(String propertyName, Object newValue) { println "Setting property '${propertyName}' with value '${newValue}'" this.@"${propertyName}" = newValue } // Execution Setting property 'name' with value 'Iván' Setting property 'age' with value '34' Getting property 'name' Getting property 'age' Hello Iván, you're 34 } def person = new Person() person.name = "Iván" person.age = 34 println "Hello ${person.name}, you're ${person.age}"
GroovyInterceptable example (II) class Hello implements GroovyInterceptable { public Object invokeMethod(String methodName, Object args) { System.out.println "Invoking method '${methodName}' with args '${args}'" def method = metaClass.getMetaMethod(methodName, args) method?.invoke(this, args) } void sayHi(String name) { System.out.println "Hello ${name}" } } def hello = new Hello() hello.sayHi("GeeCon Prague!") hello.anotherMethod() // Execution Invoking method 'sayHi' with args '[GeeCon Prague!]' Hello GeeCon Prague! Invoking method 'anotherMethod' with args '[]'
GroovyInterceptable example (II) class Hello implements GroovyInterceptable { public Object invokeMethod(String methodName, Object args) { System.out.println "Invoking method '${methodName}' with args '${args}'" def method = metaClass.getMetaMethod(methodName, args) method?.invoke(this, args) } void sayHi(String name) { System.out.println "Hello ${name}" } } def hello = new Hello() hello.sayHi("GeeCon Prague!") hello.anotherMethod() // Execution Invoking method 'sayHi' with args '[GeeCon Prague!]' Hello GeeCon Prague! Invoking method 'anotherMethod' with args '[]'
GroovyInterceptable example (II) class Hello implements GroovyInterceptable { public Object invokeMethod(String methodName, Object args) { System.out.println "Invoking method '${methodName}' with args '${args}'" def method = metaClass.getMetaMethod(methodName, args) method?.invoke(this, args) } void sayHi(String name) { System.out.println "Hello ${name}" } } def hello = new Hello() hello.sayHi("GeeCon Prague!") hello.anotherMethod() // Execution Invoking method 'sayHi' with args '[GeeCon Prague!]' Hello GeeCon Prague! Invoking method 'anotherMethod' with args '[]'
GroovyInterceptable example (II) class Hello implements GroovyInterceptable { public Object invokeMethod(String methodName, Object args) { System.out.println "Invoking method '${methodName}' with args '${args}'" def method = metaClass.getMetaMethod(methodName, args) method?.invoke(this, args) } void sayHi(String name) { System.out.println "Hello ${name}" } } def hello = new Hello() hello.sayHi("GeeCon Prague!") hello.anotherMethod() // Execution Invoking method 'sayHi' with args '[GeeCon Prague!]' Hello GeeCon Prague! Invoking method 'anotherMethod' with args '[]'
MetaClass ▷ MetaClass registry for each class ▷ Collection of methods/properties ▷ We can always modify the metaclass ▷ Intercept methods implementing invokeMethod on metaclass
MetaClass example class Hello { void sayHi(String name) { println "Hello ${name}" } } Hello.metaClass.invokeMethod = { String methodName, args -> println "Invoking method '${methodName}' with args '${args}'" def method = Hello.metaClass.getMetaMethod(methodName, args) method?.invoke(delegate, args) } def hello = new Hello() hello.sayHi("GeeCon Prague!") hello.anotherMethod() // Execution Invoking method 'sayHi' with args '[GeeCon Prague!]' Hello GeeCon Prague! Invoking method 'anotherMethod' with args '[]'
MetaClass example class Hello { void sayHi(String name) { println "Hello ${name}" } } Hello.metaClass.invokeMethod = { String methodName, args -> println "Invoking method '${methodName}' with args '${args}'" def method = Hello.metaClass.getMetaMethod(methodName, args) method?.invoke(delegate, args) } def hello = new Hello() hello.sayHi("GeeCon Prague!") hello.anotherMethod() // Execution Invoking method 'sayHi' with args '[GeeCon Prague!]' Hello GeeCon Prague! Invoking method 'anotherMethod' with args '[]'
MetaClass example class Hello { void sayHi(String name) { println "Hello ${name}" } } Hello.metaClass.invokeMethod = { String methodName, args -> println "Invoking method '${methodName}' with args '${args}'" def method = Hello.metaClass.getMetaMethod(methodName, args) method?.invoke(delegate, args) } def hello = new Hello() hello.sayHi("GeeCon Prague!") hello.anotherMethod() // Execution Invoking method 'sayHi' with args '[GeeCon Prague!]' Hello GeeCon Prague! Invoking method 'anotherMethod' with args '[]'
MetaClass example class Hello { void sayHi(String name) { println "Hello ${name}" } } Hello.metaClass.invokeMethod = { String methodName, args -> println "Invoking method '${methodName}' with args '${args}'" def method = Hello.metaClass.getMetaMethod(methodName, args) method?.invoke(delegate, args) } def hello = new Hello() hello.sayHi("GeeCon Prague!") hello.anotherMethod() // Execution Invoking method 'sayHi' with args '[GeeCon Prague!]' Hello GeeCon Prague! Invoking method 'anotherMethod' with args '[]'
MetaClass example class Hello { void sayHi(String name) { println "Hello ${name}" } } Hello.metaClass.invokeMethod = { String methodName, args -> println "Invoking method '${methodName}' with args '${args}'" def method = Hello.metaClass.getMetaMethod(methodName, args) method?.invoke(delegate, args) } def hello = new Hello() hello.sayHi("GeeCon Prague!") hello.anotherMethod() // Execution Invoking method 'sayHi' with args '[GeeCon Prague!]' Hello GeeCon Prague! Invoking method 'anotherMethod' with args '[]'
MOP method injection
MOP Method Injection ▷ Injecting methods at code-writing time ▷ We can “open” a class any time ▷ Different techniques: – MetaClass – Categories – Extensions – Mixins vs Traits
Adding methods using MetaClass class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') } } String chuckIpsum = "If you can see Chuck Norris, he can see you. If you can not see Chuck Norris you may be only seconds away from death" println StringUtils.truncate(chuckIpsum, 72) println StringUtils.truncate(chuckIpsum, 72, true) // Execution If you can see Chuck Norris, he can see you. If you can not see Chuck No If you can see Chuck Norris, he can see you. If you can not see Chuck No... String.metaClass.truncate = { Integer length, Boolean overflow = false -> delegate.take(length) + (overflow ? '...' : '') } assert chuckIpsum.truncate(72, true) == StringUtils.truncate(chuckIpsum, 72, true)
Adding methods using MetaClass class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') } } String chuckIpsum = "If you can see Chuck Norris, he can see you. If you can not see Chuck Norris you may be only seconds away from death" println StringUtils.truncate(chuckIpsum, 72) println StringUtils.truncate(chuckIpsum, 72, true) // Execution If you can see Chuck Norris, he can see you. If you can not see Chuck No If you can see Chuck Norris, he can see you. If you can not see Chuck No... String.metaClass.truncate = { Integer length, Boolean overflow = false -> delegate.take(length) + (overflow ? '...' : '') } assert chuckIpsum.truncate(72, true) == StringUtils.truncate(chuckIpsum, 72, true)
Adding methods using MetaClass class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') } } String chuckIpsum = "If you can see Chuck Norris, he can see you. If you can not see Chuck Norris you may be only seconds away from death" println StringUtils.truncate(chuckIpsum, 72) println StringUtils.truncate(chuckIpsum, 72, true) // Execution If you can see Chuck Norris, he can see you. If you can not see Chuck No If you can see Chuck Norris, he can see you. If you can not see Chuck No... String.metaClass.truncate = { Integer length, Boolean overflow = false -> delegate.take(length) + (overflow ? '...' : '') } assert chuckIpsum.truncate(72, true) == StringUtils.truncate(chuckIpsum, 72, true)
Adding methods using MetaClass class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') } } String chuckIpsum = "If you can see Chuck Norris, he can see you. If you can not see Chuck Norris you may be only seconds away from death" println StringUtils.truncate(chuckIpsum, 72) println StringUtils.truncate(chuckIpsum, 72, true) // Execution If you can see Chuck Norris, he can see you. If you can not see Chuck No If you can see Chuck Norris, he can see you. If you can not see Chuck No... String.metaClass.truncate = { Integer length, Boolean overflow = false -> delegate.take(length) + (overflow ? '...' : '') } assert chuckIpsum.truncate(72, true) == StringUtils.truncate(chuckIpsum, 72, true)
Adding methods using MetaClass class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') } } String chuckIpsum = "If you can see Chuck Norris, he can see you. If you can not see Chuck Norris you may be only seconds away from death" println StringUtils.truncate(chuckIpsum, 72) println StringUtils.truncate(chuckIpsum, 72, true) // Execution If you can see Chuck Norris, he can see you. If you can not see Chuck No If you can see Chuck Norris, he can see you. If you can not see Chuck No... String.metaClass.truncate = { Integer length, Boolean overflow = false -> delegate.take(length) + (overflow ? '...' : '') } assert chuckIpsum.truncate(72, true) == StringUtils.truncate(chuckIpsum, 72, true)
Adding methods using MetaClass class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') } } String chuckIpsum = "If you can see Chuck Norris, he can see you. If you can not see Chuck Norris you may be only seconds away from death" println StringUtils.truncate(chuckIpsum, 72) println StringUtils.truncate(chuckIpsum, 72, true) // Execution If you can see Chuck Norris, he can see you. If you can not see Chuck No If you can see Chuck Norris, he can see you. If you can not see Chuck No... String.metaClass.truncate = { Integer length, Boolean overflow = false -> delegate.take(length) + (overflow ? '...' : '') } assert chuckIpsum.truncate(72, true) == StringUtils.truncate(chuckIpsum, 72, true)
Adding properties using MetaClass class Utils { } def utilsInstance = new Utils() Utils.metaClass.version = "3.0" utilsInstance.metaClass.released = true assert utilsInstance.version == "3.0" assert utilsInstance.released == true
Adding properties using MetaClass class Utils { } def utilsInstance = new Utils() Utils.metaClass.version = "3.0" utilsInstance.metaClass.released = true assert utilsInstance.version == "3.0" assert utilsInstance.released == true
Adding properties using MetaClass class Utils { } def utilsInstance = new Utils() Utils.metaClass.version = "3.0" utilsInstance.metaClass.released = true assert utilsInstance.version == "3.0" assert utilsInstance.released == true
Adding properties using MetaClass class Utils { } def utilsInstance = new Utils() Utils.metaClass.version = "3.0" utilsInstance.metaClass.released = true assert utilsInstance.version == "3.0" assert utilsInstance.released == true
Overriding methods using MetaClass // Integer assert '42' == 42.toString() Integer.metaClass.toString = { delegate == 42 ? 'The answer to life, the universe and everything' : String.valueOf(delegate) } assert 42.toString() == 'The answer to life, the universe and everything' assert 100.toString() == '100' // Boolean assert false.toBoolean() == false Boolean.metaClass.toBoolean = { !delegate } assert false.toBoolean() == true
Overriding methods using MetaClass // Integer assert '42' == 42.toString() Integer.metaClass.toString = { delegate == 42 ? 'The answer to life, the universe and everything' : String.valueOf(delegate) } assert 42.toString() == 'The answer to life, the universe and everything' assert 100.toString() == '100' // Boolean assert false.toBoolean() == false Boolean.metaClass.toBoolean = { !delegate } assert false.toBoolean() == true
Overriding methods using MetaClass // Integer assert '42' == 42.toString() Integer.metaClass.toString = { delegate == 42 ? 'The answer to life, the universe and everything' : String.valueOf(delegate) } assert 42.toString() == 'The answer to life, the universe and everything' assert 100.toString() == '100' // Boolean assert false.toBoolean() == false Boolean.metaClass.toBoolean = { !delegate } assert false.toBoolean() == true
Overriding methods using MetaClass // Integer assert '42' == 42.toString() Integer.metaClass.toString = { delegate == 42 ? 'The answer to life, the universe and everything' : String.valueOf(delegate) } assert 42.toString() == 'The answer to life, the universe and everything' assert 100.toString() == '100' // Boolean assert false.toBoolean() == false Boolean.metaClass.toBoolean = { !delegate } assert false.toBoolean() == true
Overriding methods using MetaClass // Integer assert '42' == 42.toString() Integer.metaClass.toString = { delegate == 42 ? 'The answer to life, the universe and everything' : String.valueOf(delegate) } assert 42.toString() == 'The answer to life, the universe and everything' assert 100.toString() == '100' // Boolean assert false.toBoolean() == false Boolean.metaClass.toBoolean = { !delegate } assert false.toBoolean() == true
Overriding methods using MetaClass // Integer assert '42' == 42.toString() Integer.metaClass.toString = { delegate == 42 ? 'The answer to life, the universe and everything' : String.valueOf(delegate) } assert 42.toString() == 'The answer to life, the universe and everything' assert 100.toString() == '100' // Boolean assert false.toBoolean() == false Boolean.metaClass.toBoolean = { !delegate } assert false.toBoolean() == true
Categories ▷ MetaClass changes are “persistent” ▷ Change metaclass in confined code ▷ MOP modified only in the closure
Categories example class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') } } use (StringUtils) { println "Lorem ipsum".truncate(5) } try { println "Lorem ipsum".truncate(5) } catch (MissingMethodException mme) { println mme } // Execution Lorem groovy.lang.MissingMethodException: No signature of method: java.lang.String.truncate() is applicable for argument types: (java.lang.Integer) values: [5] Possible solutions: concat(java.lang.String), take(int)
Categories example class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') } } use (StringUtils) { println "Lorem ipsum".truncate(5) } try { println "Lorem ipsum".truncate(5) } catch (MissingMethodException mme) { println mme } // Execution Lorem groovy.lang.MissingMethodException: No signature of method: java.lang.String.truncate() is applicable for argument types: (java.lang.Integer) values: [5] Possible solutions: concat(java.lang.String), take(int)
Categories example class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') } } use (StringUtils) { println "Lorem ipsum".truncate(5) } try { println "Lorem ipsum".truncate(5) } catch (MissingMethodException mme) { println mme } // Execution Lorem groovy.lang.MissingMethodException: No signature of method: java.lang.String.truncate() is applicable for argument types: (java.lang.Integer) values: [5] Possible solutions: concat(java.lang.String), take(int)
Categories example class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') } } use (StringUtils) { println "Lorem ipsum".truncate(5) } try { println "Lorem ipsum".truncate(5) } catch (MissingMethodException mme) { println mme } // Execution Lorem groovy.lang.MissingMethodException: No signature of method: java.lang.String.truncate() is applicable for argument types: (java.lang.Integer) values: [5] Possible solutions: concat(java.lang.String), take(int)
Categories example (II) class FileBinaryCategory { def static leftShift(File file, URL url) { def input def output try { input = url.openStream() output = new BufferedOutputStream(new FileOutputStream(file)) output << input } finally { input?.close() output?.close() } } }
Categories example (II) class FileBinaryCategory { def static leftShift(File file, URL url) { def input def output try { input = url.openStream() output = new BufferedOutputStream(new FileOutputStream(file)) output << input } finally { input?.close() output?.close() } } }
Categories example (II) class FileBinaryCategory { def static leftShift(File file, URL url) { def input def output try { File tmpFile = File.createTempFile('tmp_', '') use (FileBinaryCategory) { input = url.openStream() output = new BufferedOutputStream(new FileOutputStream(file)) output << input tmpFile << "http://groovy.codehaus.org/images/groovy-logo-medium.png".toURL() } } finally { println tmpFile // Execution /tmp/tmp_7428855173238452155 input?.close() output?.close() } } }
Categories example (II) class FileBinaryCategory { def static leftShift(File file, URL url) { def input def output try { File tmpFile = File.createTempFile('tmp_', '') use (FileBinaryCategory) { input = url.openStream() output = new BufferedOutputStream(new FileOutputStream(file)) output << input tmpFile << "http://groovy.codehaus.org/images/groovy-logo-medium.png".toURL() } } finally { println tmpFile // Execution /tmp/tmp_7428855173238452155 input?.close() output?.close() } } }
Categories example (II) class FileBinaryCategory { def static leftShift(File file, URL url) { def input def output try { File tmpFile = File.createTempFile('tmp_', '') use (FileBinaryCategory) { input = url.openStream() output = new BufferedOutputStream(new FileOutputStream(file)) output << input tmpFile << "http://groovy.codehaus.org/images/groovy-logo-medium.png".toURL() } } finally { println tmpFile // Execution /tmp/tmp_7428855173238452155 input?.close() output?.close() } } }
Categories example (II) class FileBinaryCategory { def static leftShift(File file, URL url) { def input def output try { File tmpFile = File.createTempFile('tmp_', '') use (FileBinaryCategory) { input = url.openStream() output = new BufferedOutputStream(new FileOutputStream(file)) output << input tmpFile << "http://groovy.codehaus.org/images/groovy-logo-medium.png".toURL() } } finally { println tmpFile // Execution /tmp/tmp_7428855173238452155 input?.close() output?.close() } } }
Extension modules ▷ JAR file that provides extra methods ▷ Meta-information file ▷ Put jar in classpath to enhance classes
Extension modules example // src/main/groovy/geecon2014/StringUtilsExtension.groovy package geecon2014 class StringUtilsExtension { static String truncate(String self, Integer length, Boolean overflow = false) { self.take(length) + (overflow ? '...' : '') } } # src/main/resources/META-INF/services/org.codehaus.groovy.runtime.ExtensionModule moduleName = string-utils-module moduleVersion = 0.1 extensionClasses = geecon2014.StringUtilsExtension package geecon2014 import spock.lang.Specification class StringUtilsExtensionSpec extends Specification { void 'test trucate'() { expect: "Lorem" == "Lorem ipsum".truncate(5) "Lorem..." == "Lorem ipsum".truncate(5, true) } } // Execute with: // gradle build // groovy -cp build/libs/string-extensions-1.0.jar ExtensionExample1.groovy assert "Lorem..." == "Lorem ipsum". truncate(5, true)
Extension modules example // src/main/groovy/geecon2014/StringUtilsExtension.groovy package geecon2014 class StringUtilsExtension { static String truncate(String self, Integer length, Boolean overflow = false) { self.take(length) + (overflow ? '...' : '') } } # src/main/resources/META-INF/services/org.codehaus.groovy.runtime.ExtensionModule moduleName = string-utils-module moduleVersion = 0.1 extensionClasses = geecon2014.StringUtilsExtension package geecon2014 import spock.lang.Specification class StringUtilsExtensionSpec extends Specification { void 'test trucate'() { expect: "Lorem" == "Lorem ipsum".truncate(5) "Lorem..." == "Lorem ipsum".truncate(5, true) } } // Execute with: // gradle build // groovy -cp build/libs/string-extensions-1.0.jar ExtensionExample1.groovy assert "Lorem..." == "Lorem ipsum". truncate(5, true)
Extension modules example // src/main/groovy/geecon2014/StringUtilsExtension.groovy package geecon2014 class StringUtilsExtension { static String truncate(String self, Integer length, Boolean overflow = false) { self.take(length) + (overflow ? '...' : '') } } # src/main/resources/META-INF/services/org.codehaus.groovy.runtime.ExtensionModule moduleName = string-utils-module moduleVersion = 0.1 extensionClasses = geecon2014.StringUtilsExtension package geecon2014 import spock.lang.Specification class StringUtilsExtensionSpec extends Specification { void 'test trucate'() { expect: "Lorem" == "Lorem ipsum".truncate(5) "Lorem..." == "Lorem ipsum".truncate(5, true) } } // Execute with: // gradle build // groovy -cp build/libs/string-extensions-1.0.jar ExtensionExample1.groovy assert "Lorem..." == "Lorem ipsum". truncate(5, true)
Extension modules example // src/main/groovy/geecon2014/StringUtilsExtension.groovy package geecon2014 class StringUtilsExtension { static String truncate(String self, Integer length, Boolean overflow = false) { self.take(length) + (overflow ? '...' : '') } } # src/main/resources/META-INF/services/org.codehaus.groovy.runtime.ExtensionModule moduleName = string-utils-module moduleVersion = 0.1 extensionClasses = geecon2014.StringUtilsExtension package geecon2014 import spock.lang.Specification class StringUtilsExtensionSpec extends Specification { void 'test trucate'() { expect: "Lorem" == "Lorem ipsum".truncate(5) "Lorem..." == "Lorem ipsum".truncate(5, true) } } // Execute with: // gradle build // groovy -cp build/libs/string-extensions-1.0.jar ExtensionExample1.groovy assert "Lorem..." == "Lorem ipsum". truncate(5, true)
Extension modules example // src/main/groovy/geecon2014/StringUtilsExtension.groovy package geecon2014 class StringUtilsExtension { static String truncate(String self, Integer length, Boolean overflow = false) { self.take(length) + (overflow ? '...' : '') } } # src/main/resources/META-INF/services/org.codehaus.groovy.runtime.ExtensionModule moduleName = string-utils-module moduleVersion = 0.1 extensionClasses = geecon2014.StringUtilsExtension package geecon2014 import spock.lang.Specification class StringUtilsExtensionSpec extends Specification { void 'test trucate'() { expect: "Lorem" == "Lorem ipsum".truncate(5) "Lorem..." == "Lorem ipsum".truncate(5, true) } } // Execute with: // gradle build // groovy -cp build/libs/string-extensions-1.0.jar ExtensionExample1.groovy assert "Lorem..." == "Lorem ipsum". truncate(5, true)
Mixins ▷ “Bring in” or “mix in” implementations from multiple classes ▷ Calls first routed to mixed-in class ▷ Last mixin wins ▷ Can't override methods in metaclass ▷ Not easily un-done
Mixins example class SpidermanPower { String spiderSense() { "Using spider-sense..." } } class SupermanPower { String fly() { "Flying..." } } @Mixin([SpidermanPower]) class Person {} def person = new Person() assert person.spiderSense() == "Using spider-sense..." assert !(person instanceof SpidermanPower) Person.mixin SupermanPower assert person.fly() == "Flying..." assert !(person instanceof SupermanPower)
class SupermanPower { String fly() { "Flying..." } } Mixins example class SpidermanPower { String spiderSense() { "Using spider-sense..." @Mixin([SpidermanPower]) class Person {} def person = new Person() assert person.spiderSense() == "Using spider-sense..." assert !(person instanceof SpidermanPower) Person.mixin SupermanPower assert person.fly() == "Flying..." assert !(person instanceof SupermanPower) } }
class SupermanPower { String fly() { "Flying..." } } Mixins example class SpidermanPower { String spiderSense() { "Using spider-sense..." @Mixin([SpidermanPower]) class Person {} def person = new Person() assert person.spiderSense() == "Using spider-sense..." assert !(person instanceof SpidermanPower) Person.mixin SupermanPower assert person.fly() == "Flying..." assert !(person instanceof SupermanPower) } }
class SupermanPower { String fly() { "Flying..." } } Mixins example class SpidermanPower { String spiderSense() { "Using spider-sense..." @Mixin([SpidermanPower]) class Person {} def person = new Person() assert person.spiderSense() == "Using spider-sense..." assert !(person instanceof SpidermanPower) Person.mixin SupermanPower assert person.fly() == "Flying..." assert !(person instanceof SupermanPower) } }
Mixins example class SpidermanPower { String spiderSense() { "Using spider-sense..." @Mixin([SpidermanPower]) class Person {} def person = new Person() assert person.spiderSense() == "Using spider-sense..." assert !(person instanceof SpidermanPower) Person.mixin SupermanPower assert person.fly() == "Flying..." assert !(person instanceof SupermanPower) } } class SupermanPower { String fly() { "Flying..." } }
Mixins example class SpidermanPower { String spiderSense() { "Using spider-sense..." @Mixin([SpidermanPower]) class Person {} def person = new Person() assert person.spiderSense() == "Using spider-sense..." assert !(person instanceof SpidermanPower) Person.mixin SupermanPower assert person.fly() == "Flying..." assert !(person instanceof SupermanPower) } } class SupermanPower { String fly() { "Flying..." } }
Traits ▷ Groovy 2.3+ ▷ Similar to Java 8 default methods ▷ Supported in JDK 6, 7 and 8 ▷ Stateful ▷ Composition over inheritance ▷ Documentation
Traits example trait SpidermanPower { String spiderSense() { "Using spider-sense..." class Person implements SpidermanPower {} def person = new Person() assert person.spiderSense() == "Using spider-sense..." assert person instanceof SpidermanPower def person2 = person.withTraits SupermanPower assert person2.fly() == "Flying..." assert person2 instanceof SupermanPower } } trait SupermanPower { String fly() { "Flying..." } }
Traits example trait SpidermanPower { String spiderSense() { "Using spider-sense..." class Person implements SpidermanPower {} def person = new Person() assert person.spiderSense() == "Using spider-sense..." assert person instanceof SpidermanPower def person2 = person.withTraits SupermanPower assert person2.fly() == "Flying..." assert person2 instanceof SupermanPower } } trait SupermanPower { String fly() { "Flying..." } }
Traits example trait SpidermanPower { String spiderSense() { "Using spider-sense..." class Person implements SpidermanPower {} def person = new Person() assert person.spiderSense() == "Using spider-sense..." assert person instanceof SpidermanPower def person2 = person.withTraits SupermanPower assert person2.fly() == "Flying..." assert person2 instanceof SupermanPower } } trait SupermanPower { String fly() { "Flying..." } }
Traits example trait SpidermanPower { String spiderSense() { "Using spider-sense..." class Person implements SpidermanPower {} def person = new Person() assert person.spiderSense() == "Using spider-sense..." assert person instanceof SpidermanPower def person2 = person.withTraits SupermanPower assert person2.fly() == "Flying..." assert person2 instanceof SupermanPower } } trait SupermanPower { String fly() { "Flying..." } }
MOP method synthesis
MOP Method Synthesis ▷ Dynamically figure out behaviour upon invocation ▷ It may not exist until it's called/executed ▷ “Intercept, Cache, Invoke” pattern
Check for methods and properties def p = new Person(name: 'Iván', age: 34) assert p.respondsTo('sayHi') assert p.respondsTo('sayHiTo', String) assert !p.respondsTo('goodbye') assert p.hasProperty('name') assert !p.hasProperty('country') class Person { String name Integer age String sayHi() { "Hi, my name is ${name} and I'm ${age}" } String sayHiTo(String name) { "Hi ${name}, how are you?" } }
Check for methods and properties def p = new Person(name: 'Iván', age: 34) assert p.respondsTo('sayHi') assert p.respondsTo('sayHiTo', String) assert !p.respondsTo('goodbye') assert p.hasProperty('age') assert !p.hasProperty('country') class Person { String name Integer age String sayHi() { "Hi, my name is ${name} and I'm ${age}" } String sayHiTo(String name) { "Hi ${name}, how are you?" } }
Check for methods and properties def p = new Person(name: 'Iván', age: 34) assert p.respondsTo('sayHi') assert p.respondsTo('sayHiTo', String) assert !p.respondsTo('goodbye') assert p.hasProperty('age') assert !p.hasProperty('country') class Person { String name Integer age String sayHi() { "Hi, my name is ${name} and I'm ${age}" } String sayHiTo(String name) { "Hi ${name}, how are you?" } }
Check for methods and properties class Person { String name Integer age String sayHi() { "Hi, my name is ${name} and I'm ${age}" } String sayHiTo(String name) { "Hi ${name}, how are you?" } } def p = new Person(name: 'Iván', age: 34) assert p.respondsTo('sayHi') assert p.respondsTo('sayHiTo', String) assert !p.respondsTo('goodbye') assert p.hasProperty('age') assert !p.hasProperty('country')
MethodMissing example ▷ Requirements: – Send notifications to users by different channels – +50 notifications – Not all notifications by all channels – Extensible and open to future modifications
MethodMissing example abstract class Channel { void sendNewFollower(String username, String follower) { } void sendNewMessage(String username, String msg) { } ... } class EmailChannel extends Channel { void sendNewFollower(String username, String follower) { println "Sending email notification to '${username}' for new follower '${follower}'" } void sendNewMessage(String username, String msg) { println "Sending email notification to '${username}' for new message '${msg}'" } } class MobilePushChannel extends Channel { void sendNewFollower(String username, String follower) { println "Sending mobile push notification to '${username}' for new follower '${follower}'" } }
MethodMissing example abstract class Channel { void sendNewFollower(String username, String follower) { } void sendNewMessage(String username, String msg) { } ... } class EmailChannel extends Channel { void sendNewFollower(String username, String follower) { println "Sending email notification to '${username}' for new follower '${follower}'" } void sendNewMessage(String username, String msg) { println "Sending email notification to '${username}' for new message '${msg}'" } } class MobilePushChannel extends Channel { void sendNewFollower(String username, String follower) { println "Sending mobile push notification to '${username}' for new follower '${follower}'" } }
MethodMissing example abstract class Channel { void sendNewFollower(String username, String follower) { } void sendNewMessage(String username, String msg) { } ... } class EmailChannel extends Channel { void sendNewFollower(String username, String follower) { println "Sending email notification to '${username}' for new follower '${follower}'" } void sendNewMessage(String username, String msg) { println "Sending email notification to '${username}' for new message '${msg}'" } } class MobilePushChannel extends Channel { void sendNewFollower(String username, String follower) { println "Sending mobile push notification to '${username}' for new follower '${follower}'" } }
MethodMissing example class NotificationService { List channels = [] def methodMissing(String name, args) { System.out.println "...methodMissing called for ${name} with args ${args}" // Generate the implementation def implementation = { Object[] methodArgs -> channels.each { channel -> def metaMethod = channel.metaClass.getMetaMethod(name, methodArgs) return metaMethod.invoke(channel, methodArgs) } } // Cache the implementation in the metaClass NotificationService instance = this instance.metaClass."$name" = implementation // Execute it! implementation(args) } }
MethodMissing example class NotificationService { List channels = [] def methodMissing(String name, args) { System.out.println "...methodMissing called for ${name} with args ${args}" // Generate the implementation def implementation = { Object[] methodArgs -> channels.each { channel -> def metaMethod = channel.metaClass.getMetaMethod(name, methodArgs) return metaMethod.invoke(channel, methodArgs) } } // Cache the implementation in the metaClass NotificationService instance = this instance.metaClass."$name" = implementation // Execute it! implementation(args) } }
MethodMissing example class NotificationService { List channels = [] def methodMissing(String name, args) { System.out.println "...methodMissing called for ${name} with args ${args}" // Generate the implementation def implementation = { Object[] methodArgs -> channels.each { channel -> def metaMethod = channel.metaClass.getMetaMethod(name, methodArgs) return metaMethod.invoke(channel, methodArgs) } } // Cache the implementation in the metaClass NotificationService instance = this instance.metaClass."$name" = implementation // Execute it! implementation(args) } } notificationService.sendNewFollower(...) notificationService.sendNewMessage(...)
MethodMissing example class NotificationService { List channels = [] def methodMissing(String name, args) { System.out.println "...methodMissing called for ${name} with args ${args}" // Generate the implementation def implementation = { Object[] methodArgs -> channels.each { channel -> def metaMethod = channel.metaClass.getMetaMethod(name, methodArgs) return metaMethod.invoke(channel, methodArgs) } } // Cache the implementation in the metaClass NotificationService instance = this instance.metaClass."$name" = implementation // Execute it! implementation(args) } }
MethodMissing example class NotificationService { List channels = [] def methodMissing(String name, args) { System.out.println "...methodMissing called for ${name} with args ${args}" // Generate the implementation def implementation = { Object[] methodArgs -> channels.each { channel -> def metaMethod = channel.metaClass.getMetaMethod(name, methodArgs) return metaMethod.invoke(channel, methodArgs) } } // Cache the implementation in the metaClass NotificationService instance = this instance.metaClass."$name" = implementation // Execute it! implementation(args) } }
MethodMissing example def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()] ) assert !notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("John", "Peter") assert notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("Mary", "Steve") notificationService.sendNewMessage("Iván", "Hello!") // Execution ...methodMissing called for sendNewFollower with args [John, Peter] Sending email notification to 'John' for new follower 'Peter' Sending mobile push notification to 'John' for new follower 'Peter' Sending email notification to 'Mary' for new follower 'Steve' Sending mobile push notification to 'Mary' for new follower 'Steve' ...methodMissing called for sendNewMessage with args [Iván, Hello!] Sending email notification to 'Iván' for new message 'Hello!'
MethodMissing example def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()] ) assert !notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("John", "Peter") assert notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("Mary", "Steve") notificationService.sendNewMessage("Iván", "Hello!") // Execution ...methodMissing called for sendNewFollower with args [John, Peter] Sending email notification to 'John' for new follower 'Peter' Sending mobile push notification to 'John' for new follower 'Peter' Sending email notification to 'Mary' for new follower 'Steve' Sending mobile push notification to 'Mary' for new follower 'Steve' ...methodMissing called for sendNewMessage with args [Iván, Hello!] Sending email notification to 'Iván' for new message 'Hello!'
MethodMissing example def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()] ) assert !notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("John", "Peter") assert notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("Mary", "Steve") notificationService.sendNewMessage("Iván", "Hello!") // Execution ...methodMissing called for sendNewFollower with args [John, Peter] Sending email notification to 'John' for new follower 'Peter' Sending mobile push notification to 'John' for new follower 'Peter' Sending email notification to 'Mary' for new follower 'Steve' Sending mobile push notification to 'Mary' for new follower 'Steve' ...methodMissing called for sendNewMessage with args [Iván, Hello!] Sending email notification to 'Iván' for new message 'Hello!'
MethodMissing example def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()] ) assert !notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("John", "Peter") assert notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("Mary", "Steve") notificationService.sendNewMessage("Iván", "Hello!") // Execution ...methodMissing called for sendNewFollower with args [John, Peter] Sending email notification to 'John' for new follower 'Peter' Sending mobile push notification to 'John' for new follower 'Peter' Sending email notification to 'Mary' for new follower 'Steve' Sending mobile push notification to 'Mary' for new follower 'Steve' ...methodMissing called for sendNewMessage with args [Iván, Hello!] Sending email notification to 'Iván' for new message 'Hello!'
MethodMissing example def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()] ) assert !notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("John", "Peter") assert notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("Mary", "Steve") notificationService.sendNewMessage("class EmailChannel exItveánnd"s, C"hHaenlnleol! "{) void sendNewFollower(String username, String follower) {…} void sendNewMessage(String username, String msg) {…} // Execution ...} methodMissing called for sendNewFollower with args [John, Peter] Sending email notification to 'John' for new follower 'Peter' Sending class mobile MobilePushChannel push notification extends to Channel 'John' { for new follower 'Peter' void sendNewFollower(String username, String follower) {…} Sending } email notification to 'Mary' for new follower 'Steve' Sending mobile push notification to 'Mary' for new follower 'Steve' ...methodMissing called for sendNewMessage with args [Iván, Hello!] Sending email notification to 'Iván' for new message 'Hello!'
MethodMissing example def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()] ) assert !notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("John", "Peter") assert notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("Mary", "Steve") notificationService.sendNewMessage("Iván", "Hello!") // Execution ...methodMissing called for sendNewFollower with args [John, Peter] Sending email notification to 'John' for new follower 'Peter' Sending mobile push notification to 'John' for new follower 'Peter' Sending email notification to 'Mary' for new follower 'Steve' Sending mobile push notification to 'Mary' for new follower 'Steve' ...methodMissing called for sendNewMessage with args [Iván, Hello!] Sending email notification to 'Iván' for new message 'Hello!'
MethodMissing example def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()] ) assert !notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("John", "Peter") assert notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("Mary", "Steve") notificationService.sendNewMessage("Iván", "Hello!") // Execution ...methodMissing called for sendNewFollower with args [John, Peter] Sending email notification to 'John' for new follower 'Peter' Sending mobile push notification to 'John' for new follower 'Peter' Sending email notification to 'Mary' for new follower 'Steve' Sending mobile push notification to 'Mary' for new follower 'Steve' ...methodMissing called for sendNewMessage with args [Iván, Hello!] Sending email notification to 'Iván' for new message 'Hello!'
MethodMissing example def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()] ) assert !notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("John", "Peter") assert notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("Mary", "Steve") notificationService.sendNewMessage("Iván", "Hello!") // Execution ...methodMissing called for sendNewFollower with args [John, Peter] Sending email notification to 'John' for new follower 'Peter' Sending mobile push notification to 'John' for new follower 'Peter' Sending email notification to 'Mary' for new follower 'Steve' Sending mobile push notification to 'Mary' for new follower 'Steve' ...methodMissing called for sendNewMessage with args [Iván, Hello!] Sending email notification to 'Iván' for new message 'Hello!'
2. Compile-time metaprogramming
Compile-time metaprogramming ▷ Advance feature ▷ Analyze/modify program structure at compile time ▷ Cross-cutting features ▷ Write code that generates bytecode
AST and compilation ▷ AST: Abstract Syntax Tree ▷ AST modified during compilation ▷ Hook into the phases ▷ Initialization, Parsing, Conversion, Semantic analysis, Canonicalization, Instruction selection, Class generation, Output, Finalization
Groovy AST Transformations ▷ Lot of AST transformations out-of-the-box ▷ @EqualsAndHashCode, @ToString, @TuppleConstructor, @Canonical, @Grab, @Immutable, @Delegate, @Singleton, @Category, @Log4j, @CompileStatic, @TypeChecked, @Synchronized ...
Global AST transformations
Global AST Transformations ▷ No annotation ▷ Meta-information file ▷ Applied to all code during compilation ▷ Any compilation phase ▷ Grails uses intensively in GORM
Local AST transformations
Local AST Transformations ▷ Annotate code ▷ No meta-information file ▷ Easy to debug
Steps to create local AST Interface AST Enjoy!
Local AST example import geecon2014.Version @Version('1.0') class VersionedClass { } package geecon2014 import ... @Retention(RetentionPolicy.SOURCE) @Target([ElementType.TYPE]) @GroovyASTTransformationClass("geecon2014.VersionASTTransformation") @interface Version { String value() } class VersionedClass { public static final String VERSION = "1.0" }
Local AST example import geecon2014.Version @Version('1.0') class VersionedClass { } package geecon2014 import ... @Retention(RetentionPolicy.SOURCE) @Target([ElementType.TYPE]) @GroovyASTTransformationClass("geecon2014.VersionASTTransformation") @interface Version { String value() } class VersionedClass { public static final String VERSION = "1.0" }
Local AST example import geecon2014.Version @Version('1.0') class VersionedClass { } package geecon2014 import ... @Retention(RetentionPolicy.SOURCE) @Target([ElementType.TYPE]) @GroovyASTTransformationClass("geecon2014.VersionASTTransformation") @interface Version { String value() } class VersionedClass { public static final String VERSION = "1.0" }
Local AST example @GroovyASTTransformation(phase = CompilePhase.SEMANTIC_ANALYSIS) class VersionASTTransformation extends AbstractASTTransformation { @Override public void visit(final ASTNode[] nodes, final SourceUnit source) { if (nodes.length != 2) { return } if (nodes[0] instanceof AnnotationNode && nodes[1] instanceof ClassNode) { def annotation = nodes[0] def version = annotation.getMember('value') if (version instanceof ConstantExpression) { nodes[1].addField('VERSION', ACC_PUBLIC | ACC_STATIC | ACC_FINAL, ClassHelper.STRING_TYPE, version) } else { source.addError(new SyntaxException("Invalid value for annotation", annotation.lineNumber, annotation.columnNumber)) } } } }
Local AST example @GroovyASTTransformation(phase = CompilePhase.SEMANTIC_ANALYSIS) class VersionASTTransformation extends AbstractASTTransformation { @Override public void visit(final ASTNode[] nodes, final SourceUnit source) { if (nodes.length != 2) { return } if (nodes[0] instanceof AnnotationNode && nodes[1] instanceof ClassNode) { def annotation = nodes[0] def version = annotation.getMember('value') if (version instanceof ConstantExpression) { nodes[1].addField('VERSION', ACC_PUBLIC | ACC_STATIC | ACC_FINAL, ClassHelper.STRING_TYPE, version) } else { source.addError(new SyntaxException("Invalid value for annotation", annotation.lineNumber, annotation.columnNumber)) } } } }
Local AST example // Execute with: // gradle build // groovy -cp build/libs/add-version-1.0.jar LocalASTExample.groovy import geecon.Version @Version('1.0') class VersionedClass { } println VersionedClass.VERSION // Execution 1.0
Local AST example // Execute with: // gradle build // groovy -cp build/libs/add-version-1.0.jar LocalASTExample.groovy import geecon.Version @Version('1.0') class VersionedClass { } println VersionedClass.VERSION // Execution 1.0
Local AST example // Execute with: // gradle build // groovy -cp build/libs/add-version-1.0.jar LocalASTExample.groovy import geecon.Version @Version('1.0') class VersionedClass { } println VersionedClass.VERSION // Execution 1.0
3. Recap Why we should use metaprogramming?
Let’s review some concepts Metaprogramming out-of-the box Easy and very powerfull Write better code Add behaviour easily Take advantage of this power Because Groovy, it's groovy
With great power comes great responsibility
Thanks! Any questions? Iván López @ilopmar lopez.ivan@gmail.com https://github.com/lmivan http://kcy.me/1bzj7

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GeeCON Prague 2014 - Metaprogramming with Groovy

  • 1. Iván López @ilopmar METAPROGRAMMING WITH GROOVY
  • 2. Hello! I am Iván López @ilopmar
  • 3. Groovy is dynamic ▷ “Delay” to runtime some decisions ▷ Add properties/behaviours in runtime ▷ Wide range of applicability
  • 5. “ Metaprogramming is the writing of computer programs that write or manipulate other programs (or themselves) as their data. - Wikipedia
  • 7. Runtime metaprogramming ▷ Groovy provides this through Meta-Object Protocol (MOP) ▷ Use MOP to: – Invoke methods dynamically – Synthesize classes and methods on the fly
  • 8. What is the Meta Object Protocol? Groovy Groovy Java Java MOP
  • 10. Groovy Interceptable ▷ GroovyObject interface ▷ Implement GroovyInterceptable to hook into the execution public interface GroovyObject { Object invokeMethod(String name, Object args) Object getProperty(String propertyName) void setProperty(String propertyName, Object newValue) MetaClass getMetaClass() void setMetaClass(MetaClass metaClass) }
  • 11. GroovyInterceptable example class Person implements GroovyInterceptable { String name Integer age public Object getProperty(String propertyName) { println "Getting property '${propertyName}'" return this.@"${propertyName}" } public void setProperty(String propertyName, Object newValue) { println "Setting property '${propertyName}' with value '${newValue}'" this.@"${propertyName}" = newValue } // Execution Setting property 'name' with value 'Iván' Setting property 'age' with value '34' Getting property 'name' Getting property 'age' Hello Iván, you're 34 } def person = new Person() person.name = "Iván" person.age = 34 println "Hello ${person.name}, you're ${person.age}"
  • 12. GroovyInterceptable example class Person implements GroovyInterceptable { String name Integer age public Object getProperty(String propertyName) { println "Getting property '${propertyName}'" return this.@"${propertyName}" } public void setProperty(String propertyName, Object newValue) { println "Setting property '${propertyName}' with value '${newValue}'" this.@"${propertyName}" = newValue } // Execution Setting property 'name' with value 'Iván' Setting property 'age' with value '34' Getting property 'name' Getting property 'age' Hello Iván, you're 34 } def person = new Person() person.name = "Iván" person.age = 34 println "Hello ${person.name}, you're ${person.age}"
  • 13. GroovyInterceptable example class Person implements GroovyInterceptable { String name Integer age public Object getProperty(String propertyName) { println "Getting property '${propertyName}'" return this.@"${propertyName}" } public void setProperty(String propertyName, Object newValue) { println "Setting property '${propertyName}' with value '${newValue}'" this.@"${propertyName}" = newValue } // Execution Setting property 'name' with value 'Iván' Setting property 'age' with value '34' Getting property 'name' Getting property 'age' Hello Iván, you're 34 } def person = new Person() person.name = "Iván" person.age = 34 println "Hello ${person.name}, you're ${person.age}"
  • 14. GroovyInterceptable example class Person implements GroovyInterceptable { String name Integer age public Object getProperty(String propertyName) { println "Getting property '${propertyName}'" return this.@"${propertyName}" } public void setProperty(String propertyName, Object newValue) { println "Setting property '${propertyName}' with value '${newValue}'" this.@"${propertyName}" = newValue } // Execution Setting property 'name' with value 'Iván' Setting property 'age' with value '34' Getting property 'name' Getting property 'age' Hello Iván, you're 34 } def person = new Person() person.name = "Iván" person.age = 34 println "Hello ${person.name}, you're ${person.age}"
  • 15. GroovyInterceptable example class Person implements GroovyInterceptable { String name Integer age public Object getProperty(String propertyName) { println "Getting property '${propertyName}'" return this.@"${propertyName}" } public void setProperty(String propertyName, Object newValue) { println "Setting property '${propertyName}' with value '${newValue}'" this.@"${propertyName}" = newValue } // Execution Setting property 'name' with value 'Iván' Setting property 'age' with value '34' Getting property 'name' Getting property 'age' Hello Iván, you're 34 } def person = new Person() person.name = "Iván" person.age = 34 println "Hello ${person.name}, you're ${person.age}"
  • 16. GroovyInterceptable example (II) class Hello implements GroovyInterceptable { public Object invokeMethod(String methodName, Object args) { System.out.println "Invoking method '${methodName}' with args '${args}'" def method = metaClass.getMetaMethod(methodName, args) method?.invoke(this, args) } void sayHi(String name) { System.out.println "Hello ${name}" } } def hello = new Hello() hello.sayHi("GeeCon Prague!") hello.anotherMethod() // Execution Invoking method 'sayHi' with args '[GeeCon Prague!]' Hello GeeCon Prague! Invoking method 'anotherMethod' with args '[]'
  • 17. GroovyInterceptable example (II) class Hello implements GroovyInterceptable { public Object invokeMethod(String methodName, Object args) { System.out.println "Invoking method '${methodName}' with args '${args}'" def method = metaClass.getMetaMethod(methodName, args) method?.invoke(this, args) } void sayHi(String name) { System.out.println "Hello ${name}" } } def hello = new Hello() hello.sayHi("GeeCon Prague!") hello.anotherMethod() // Execution Invoking method 'sayHi' with args '[GeeCon Prague!]' Hello GeeCon Prague! Invoking method 'anotherMethod' with args '[]'
  • 18. GroovyInterceptable example (II) class Hello implements GroovyInterceptable { public Object invokeMethod(String methodName, Object args) { System.out.println "Invoking method '${methodName}' with args '${args}'" def method = metaClass.getMetaMethod(methodName, args) method?.invoke(this, args) } void sayHi(String name) { System.out.println "Hello ${name}" } } def hello = new Hello() hello.sayHi("GeeCon Prague!") hello.anotherMethod() // Execution Invoking method 'sayHi' with args '[GeeCon Prague!]' Hello GeeCon Prague! Invoking method 'anotherMethod' with args '[]'
  • 19. GroovyInterceptable example (II) class Hello implements GroovyInterceptable { public Object invokeMethod(String methodName, Object args) { System.out.println "Invoking method '${methodName}' with args '${args}'" def method = metaClass.getMetaMethod(methodName, args) method?.invoke(this, args) } void sayHi(String name) { System.out.println "Hello ${name}" } } def hello = new Hello() hello.sayHi("GeeCon Prague!") hello.anotherMethod() // Execution Invoking method 'sayHi' with args '[GeeCon Prague!]' Hello GeeCon Prague! Invoking method 'anotherMethod' with args '[]'
  • 20. MetaClass ▷ MetaClass registry for each class ▷ Collection of methods/properties ▷ We can always modify the metaclass ▷ Intercept methods implementing invokeMethod on metaclass
  • 21. MetaClass example class Hello { void sayHi(String name) { println "Hello ${name}" } } Hello.metaClass.invokeMethod = { String methodName, args -> println "Invoking method '${methodName}' with args '${args}'" def method = Hello.metaClass.getMetaMethod(methodName, args) method?.invoke(delegate, args) } def hello = new Hello() hello.sayHi("GeeCon Prague!") hello.anotherMethod() // Execution Invoking method 'sayHi' with args '[GeeCon Prague!]' Hello GeeCon Prague! Invoking method 'anotherMethod' with args '[]'
  • 22. MetaClass example class Hello { void sayHi(String name) { println "Hello ${name}" } } Hello.metaClass.invokeMethod = { String methodName, args -> println "Invoking method '${methodName}' with args '${args}'" def method = Hello.metaClass.getMetaMethod(methodName, args) method?.invoke(delegate, args) } def hello = new Hello() hello.sayHi("GeeCon Prague!") hello.anotherMethod() // Execution Invoking method 'sayHi' with args '[GeeCon Prague!]' Hello GeeCon Prague! Invoking method 'anotherMethod' with args '[]'
  • 23. MetaClass example class Hello { void sayHi(String name) { println "Hello ${name}" } } Hello.metaClass.invokeMethod = { String methodName, args -> println "Invoking method '${methodName}' with args '${args}'" def method = Hello.metaClass.getMetaMethod(methodName, args) method?.invoke(delegate, args) } def hello = new Hello() hello.sayHi("GeeCon Prague!") hello.anotherMethod() // Execution Invoking method 'sayHi' with args '[GeeCon Prague!]' Hello GeeCon Prague! Invoking method 'anotherMethod' with args '[]'
  • 24. MetaClass example class Hello { void sayHi(String name) { println "Hello ${name}" } } Hello.metaClass.invokeMethod = { String methodName, args -> println "Invoking method '${methodName}' with args '${args}'" def method = Hello.metaClass.getMetaMethod(methodName, args) method?.invoke(delegate, args) } def hello = new Hello() hello.sayHi("GeeCon Prague!") hello.anotherMethod() // Execution Invoking method 'sayHi' with args '[GeeCon Prague!]' Hello GeeCon Prague! Invoking method 'anotherMethod' with args '[]'
  • 25. MetaClass example class Hello { void sayHi(String name) { println "Hello ${name}" } } Hello.metaClass.invokeMethod = { String methodName, args -> println "Invoking method '${methodName}' with args '${args}'" def method = Hello.metaClass.getMetaMethod(methodName, args) method?.invoke(delegate, args) } def hello = new Hello() hello.sayHi("GeeCon Prague!") hello.anotherMethod() // Execution Invoking method 'sayHi' with args '[GeeCon Prague!]' Hello GeeCon Prague! Invoking method 'anotherMethod' with args '[]'
  • 27. MOP Method Injection ▷ Injecting methods at code-writing time ▷ We can “open” a class any time ▷ Different techniques: – MetaClass – Categories – Extensions – Mixins vs Traits
  • 28. Adding methods using MetaClass class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') } } String chuckIpsum = "If you can see Chuck Norris, he can see you. If you can not see Chuck Norris you may be only seconds away from death" println StringUtils.truncate(chuckIpsum, 72) println StringUtils.truncate(chuckIpsum, 72, true) // Execution If you can see Chuck Norris, he can see you. If you can not see Chuck No If you can see Chuck Norris, he can see you. If you can not see Chuck No... String.metaClass.truncate = { Integer length, Boolean overflow = false -> delegate.take(length) + (overflow ? '...' : '') } assert chuckIpsum.truncate(72, true) == StringUtils.truncate(chuckIpsum, 72, true)
  • 29. Adding methods using MetaClass class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') } } String chuckIpsum = "If you can see Chuck Norris, he can see you. If you can not see Chuck Norris you may be only seconds away from death" println StringUtils.truncate(chuckIpsum, 72) println StringUtils.truncate(chuckIpsum, 72, true) // Execution If you can see Chuck Norris, he can see you. If you can not see Chuck No If you can see Chuck Norris, he can see you. If you can not see Chuck No... String.metaClass.truncate = { Integer length, Boolean overflow = false -> delegate.take(length) + (overflow ? '...' : '') } assert chuckIpsum.truncate(72, true) == StringUtils.truncate(chuckIpsum, 72, true)
  • 30. Adding methods using MetaClass class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') } } String chuckIpsum = "If you can see Chuck Norris, he can see you. If you can not see Chuck Norris you may be only seconds away from death" println StringUtils.truncate(chuckIpsum, 72) println StringUtils.truncate(chuckIpsum, 72, true) // Execution If you can see Chuck Norris, he can see you. If you can not see Chuck No If you can see Chuck Norris, he can see you. If you can not see Chuck No... String.metaClass.truncate = { Integer length, Boolean overflow = false -> delegate.take(length) + (overflow ? '...' : '') } assert chuckIpsum.truncate(72, true) == StringUtils.truncate(chuckIpsum, 72, true)
  • 31. Adding methods using MetaClass class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') } } String chuckIpsum = "If you can see Chuck Norris, he can see you. If you can not see Chuck Norris you may be only seconds away from death" println StringUtils.truncate(chuckIpsum, 72) println StringUtils.truncate(chuckIpsum, 72, true) // Execution If you can see Chuck Norris, he can see you. If you can not see Chuck No If you can see Chuck Norris, he can see you. If you can not see Chuck No... String.metaClass.truncate = { Integer length, Boolean overflow = false -> delegate.take(length) + (overflow ? '...' : '') } assert chuckIpsum.truncate(72, true) == StringUtils.truncate(chuckIpsum, 72, true)
  • 32. Adding methods using MetaClass class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') } } String chuckIpsum = "If you can see Chuck Norris, he can see you. If you can not see Chuck Norris you may be only seconds away from death" println StringUtils.truncate(chuckIpsum, 72) println StringUtils.truncate(chuckIpsum, 72, true) // Execution If you can see Chuck Norris, he can see you. If you can not see Chuck No If you can see Chuck Norris, he can see you. If you can not see Chuck No... String.metaClass.truncate = { Integer length, Boolean overflow = false -> delegate.take(length) + (overflow ? '...' : '') } assert chuckIpsum.truncate(72, true) == StringUtils.truncate(chuckIpsum, 72, true)
  • 33. Adding methods using MetaClass class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') } } String chuckIpsum = "If you can see Chuck Norris, he can see you. If you can not see Chuck Norris you may be only seconds away from death" println StringUtils.truncate(chuckIpsum, 72) println StringUtils.truncate(chuckIpsum, 72, true) // Execution If you can see Chuck Norris, he can see you. If you can not see Chuck No If you can see Chuck Norris, he can see you. If you can not see Chuck No... String.metaClass.truncate = { Integer length, Boolean overflow = false -> delegate.take(length) + (overflow ? '...' : '') } assert chuckIpsum.truncate(72, true) == StringUtils.truncate(chuckIpsum, 72, true)
  • 34. Adding properties using MetaClass class Utils { } def utilsInstance = new Utils() Utils.metaClass.version = "3.0" utilsInstance.metaClass.released = true assert utilsInstance.version == "3.0" assert utilsInstance.released == true
  • 35. Adding properties using MetaClass class Utils { } def utilsInstance = new Utils() Utils.metaClass.version = "3.0" utilsInstance.metaClass.released = true assert utilsInstance.version == "3.0" assert utilsInstance.released == true
  • 36. Adding properties using MetaClass class Utils { } def utilsInstance = new Utils() Utils.metaClass.version = "3.0" utilsInstance.metaClass.released = true assert utilsInstance.version == "3.0" assert utilsInstance.released == true
  • 37. Adding properties using MetaClass class Utils { } def utilsInstance = new Utils() Utils.metaClass.version = "3.0" utilsInstance.metaClass.released = true assert utilsInstance.version == "3.0" assert utilsInstance.released == true
  • 38. Overriding methods using MetaClass // Integer assert '42' == 42.toString() Integer.metaClass.toString = { delegate == 42 ? 'The answer to life, the universe and everything' : String.valueOf(delegate) } assert 42.toString() == 'The answer to life, the universe and everything' assert 100.toString() == '100' // Boolean assert false.toBoolean() == false Boolean.metaClass.toBoolean = { !delegate } assert false.toBoolean() == true
  • 39. Overriding methods using MetaClass // Integer assert '42' == 42.toString() Integer.metaClass.toString = { delegate == 42 ? 'The answer to life, the universe and everything' : String.valueOf(delegate) } assert 42.toString() == 'The answer to life, the universe and everything' assert 100.toString() == '100' // Boolean assert false.toBoolean() == false Boolean.metaClass.toBoolean = { !delegate } assert false.toBoolean() == true
  • 40. Overriding methods using MetaClass // Integer assert '42' == 42.toString() Integer.metaClass.toString = { delegate == 42 ? 'The answer to life, the universe and everything' : String.valueOf(delegate) } assert 42.toString() == 'The answer to life, the universe and everything' assert 100.toString() == '100' // Boolean assert false.toBoolean() == false Boolean.metaClass.toBoolean = { !delegate } assert false.toBoolean() == true
  • 41. Overriding methods using MetaClass // Integer assert '42' == 42.toString() Integer.metaClass.toString = { delegate == 42 ? 'The answer to life, the universe and everything' : String.valueOf(delegate) } assert 42.toString() == 'The answer to life, the universe and everything' assert 100.toString() == '100' // Boolean assert false.toBoolean() == false Boolean.metaClass.toBoolean = { !delegate } assert false.toBoolean() == true
  • 42. Overriding methods using MetaClass // Integer assert '42' == 42.toString() Integer.metaClass.toString = { delegate == 42 ? 'The answer to life, the universe and everything' : String.valueOf(delegate) } assert 42.toString() == 'The answer to life, the universe and everything' assert 100.toString() == '100' // Boolean assert false.toBoolean() == false Boolean.metaClass.toBoolean = { !delegate } assert false.toBoolean() == true
  • 43. Overriding methods using MetaClass // Integer assert '42' == 42.toString() Integer.metaClass.toString = { delegate == 42 ? 'The answer to life, the universe and everything' : String.valueOf(delegate) } assert 42.toString() == 'The answer to life, the universe and everything' assert 100.toString() == '100' // Boolean assert false.toBoolean() == false Boolean.metaClass.toBoolean = { !delegate } assert false.toBoolean() == true
  • 44. Categories ▷ MetaClass changes are “persistent” ▷ Change metaclass in confined code ▷ MOP modified only in the closure
  • 45. Categories example class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') } } use (StringUtils) { println "Lorem ipsum".truncate(5) } try { println "Lorem ipsum".truncate(5) } catch (MissingMethodException mme) { println mme } // Execution Lorem groovy.lang.MissingMethodException: No signature of method: java.lang.String.truncate() is applicable for argument types: (java.lang.Integer) values: [5] Possible solutions: concat(java.lang.String), take(int)
  • 46. Categories example class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') } } use (StringUtils) { println "Lorem ipsum".truncate(5) } try { println "Lorem ipsum".truncate(5) } catch (MissingMethodException mme) { println mme } // Execution Lorem groovy.lang.MissingMethodException: No signature of method: java.lang.String.truncate() is applicable for argument types: (java.lang.Integer) values: [5] Possible solutions: concat(java.lang.String), take(int)
  • 47. Categories example class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') } } use (StringUtils) { println "Lorem ipsum".truncate(5) } try { println "Lorem ipsum".truncate(5) } catch (MissingMethodException mme) { println mme } // Execution Lorem groovy.lang.MissingMethodException: No signature of method: java.lang.String.truncate() is applicable for argument types: (java.lang.Integer) values: [5] Possible solutions: concat(java.lang.String), take(int)
  • 48. Categories example class StringUtils { static String truncate(String text, Integer length, Boolean overflow = false) { text.take(length) + (overflow ? '...' : '') } } use (StringUtils) { println "Lorem ipsum".truncate(5) } try { println "Lorem ipsum".truncate(5) } catch (MissingMethodException mme) { println mme } // Execution Lorem groovy.lang.MissingMethodException: No signature of method: java.lang.String.truncate() is applicable for argument types: (java.lang.Integer) values: [5] Possible solutions: concat(java.lang.String), take(int)
  • 49. Categories example (II) class FileBinaryCategory { def static leftShift(File file, URL url) { def input def output try { input = url.openStream() output = new BufferedOutputStream(new FileOutputStream(file)) output << input } finally { input?.close() output?.close() } } }
  • 50. Categories example (II) class FileBinaryCategory { def static leftShift(File file, URL url) { def input def output try { input = url.openStream() output = new BufferedOutputStream(new FileOutputStream(file)) output << input } finally { input?.close() output?.close() } } }
  • 51. Categories example (II) class FileBinaryCategory { def static leftShift(File file, URL url) { def input def output try { File tmpFile = File.createTempFile('tmp_', '') use (FileBinaryCategory) { input = url.openStream() output = new BufferedOutputStream(new FileOutputStream(file)) output << input tmpFile << "http://groovy.codehaus.org/images/groovy-logo-medium.png".toURL() } } finally { println tmpFile // Execution /tmp/tmp_7428855173238452155 input?.close() output?.close() } } }
  • 52. Categories example (II) class FileBinaryCategory { def static leftShift(File file, URL url) { def input def output try { File tmpFile = File.createTempFile('tmp_', '') use (FileBinaryCategory) { input = url.openStream() output = new BufferedOutputStream(new FileOutputStream(file)) output << input tmpFile << "http://groovy.codehaus.org/images/groovy-logo-medium.png".toURL() } } finally { println tmpFile // Execution /tmp/tmp_7428855173238452155 input?.close() output?.close() } } }
  • 53. Categories example (II) class FileBinaryCategory { def static leftShift(File file, URL url) { def input def output try { File tmpFile = File.createTempFile('tmp_', '') use (FileBinaryCategory) { input = url.openStream() output = new BufferedOutputStream(new FileOutputStream(file)) output << input tmpFile << "http://groovy.codehaus.org/images/groovy-logo-medium.png".toURL() } } finally { println tmpFile // Execution /tmp/tmp_7428855173238452155 input?.close() output?.close() } } }
  • 54. Categories example (II) class FileBinaryCategory { def static leftShift(File file, URL url) { def input def output try { File tmpFile = File.createTempFile('tmp_', '') use (FileBinaryCategory) { input = url.openStream() output = new BufferedOutputStream(new FileOutputStream(file)) output << input tmpFile << "http://groovy.codehaus.org/images/groovy-logo-medium.png".toURL() } } finally { println tmpFile // Execution /tmp/tmp_7428855173238452155 input?.close() output?.close() } } }
  • 55. Extension modules ▷ JAR file that provides extra methods ▷ Meta-information file ▷ Put jar in classpath to enhance classes
  • 56. Extension modules example // src/main/groovy/geecon2014/StringUtilsExtension.groovy package geecon2014 class StringUtilsExtension { static String truncate(String self, Integer length, Boolean overflow = false) { self.take(length) + (overflow ? '...' : '') } } # src/main/resources/META-INF/services/org.codehaus.groovy.runtime.ExtensionModule moduleName = string-utils-module moduleVersion = 0.1 extensionClasses = geecon2014.StringUtilsExtension package geecon2014 import spock.lang.Specification class StringUtilsExtensionSpec extends Specification { void 'test trucate'() { expect: "Lorem" == "Lorem ipsum".truncate(5) "Lorem..." == "Lorem ipsum".truncate(5, true) } } // Execute with: // gradle build // groovy -cp build/libs/string-extensions-1.0.jar ExtensionExample1.groovy assert "Lorem..." == "Lorem ipsum". truncate(5, true)
  • 57. Extension modules example // src/main/groovy/geecon2014/StringUtilsExtension.groovy package geecon2014 class StringUtilsExtension { static String truncate(String self, Integer length, Boolean overflow = false) { self.take(length) + (overflow ? '...' : '') } } # src/main/resources/META-INF/services/org.codehaus.groovy.runtime.ExtensionModule moduleName = string-utils-module moduleVersion = 0.1 extensionClasses = geecon2014.StringUtilsExtension package geecon2014 import spock.lang.Specification class StringUtilsExtensionSpec extends Specification { void 'test trucate'() { expect: "Lorem" == "Lorem ipsum".truncate(5) "Lorem..." == "Lorem ipsum".truncate(5, true) } } // Execute with: // gradle build // groovy -cp build/libs/string-extensions-1.0.jar ExtensionExample1.groovy assert "Lorem..." == "Lorem ipsum". truncate(5, true)
  • 58. Extension modules example // src/main/groovy/geecon2014/StringUtilsExtension.groovy package geecon2014 class StringUtilsExtension { static String truncate(String self, Integer length, Boolean overflow = false) { self.take(length) + (overflow ? '...' : '') } } # src/main/resources/META-INF/services/org.codehaus.groovy.runtime.ExtensionModule moduleName = string-utils-module moduleVersion = 0.1 extensionClasses = geecon2014.StringUtilsExtension package geecon2014 import spock.lang.Specification class StringUtilsExtensionSpec extends Specification { void 'test trucate'() { expect: "Lorem" == "Lorem ipsum".truncate(5) "Lorem..." == "Lorem ipsum".truncate(5, true) } } // Execute with: // gradle build // groovy -cp build/libs/string-extensions-1.0.jar ExtensionExample1.groovy assert "Lorem..." == "Lorem ipsum". truncate(5, true)
  • 59. Extension modules example // src/main/groovy/geecon2014/StringUtilsExtension.groovy package geecon2014 class StringUtilsExtension { static String truncate(String self, Integer length, Boolean overflow = false) { self.take(length) + (overflow ? '...' : '') } } # src/main/resources/META-INF/services/org.codehaus.groovy.runtime.ExtensionModule moduleName = string-utils-module moduleVersion = 0.1 extensionClasses = geecon2014.StringUtilsExtension package geecon2014 import spock.lang.Specification class StringUtilsExtensionSpec extends Specification { void 'test trucate'() { expect: "Lorem" == "Lorem ipsum".truncate(5) "Lorem..." == "Lorem ipsum".truncate(5, true) } } // Execute with: // gradle build // groovy -cp build/libs/string-extensions-1.0.jar ExtensionExample1.groovy assert "Lorem..." == "Lorem ipsum". truncate(5, true)
  • 60. Extension modules example // src/main/groovy/geecon2014/StringUtilsExtension.groovy package geecon2014 class StringUtilsExtension { static String truncate(String self, Integer length, Boolean overflow = false) { self.take(length) + (overflow ? '...' : '') } } # src/main/resources/META-INF/services/org.codehaus.groovy.runtime.ExtensionModule moduleName = string-utils-module moduleVersion = 0.1 extensionClasses = geecon2014.StringUtilsExtension package geecon2014 import spock.lang.Specification class StringUtilsExtensionSpec extends Specification { void 'test trucate'() { expect: "Lorem" == "Lorem ipsum".truncate(5) "Lorem..." == "Lorem ipsum".truncate(5, true) } } // Execute with: // gradle build // groovy -cp build/libs/string-extensions-1.0.jar ExtensionExample1.groovy assert "Lorem..." == "Lorem ipsum". truncate(5, true)
  • 61. Mixins ▷ “Bring in” or “mix in” implementations from multiple classes ▷ Calls first routed to mixed-in class ▷ Last mixin wins ▷ Can't override methods in metaclass ▷ Not easily un-done
  • 62. Mixins example class SpidermanPower { String spiderSense() { "Using spider-sense..." } } class SupermanPower { String fly() { "Flying..." } } @Mixin([SpidermanPower]) class Person {} def person = new Person() assert person.spiderSense() == "Using spider-sense..." assert !(person instanceof SpidermanPower) Person.mixin SupermanPower assert person.fly() == "Flying..." assert !(person instanceof SupermanPower)
  • 63. class SupermanPower { String fly() { "Flying..." } } Mixins example class SpidermanPower { String spiderSense() { "Using spider-sense..." @Mixin([SpidermanPower]) class Person {} def person = new Person() assert person.spiderSense() == "Using spider-sense..." assert !(person instanceof SpidermanPower) Person.mixin SupermanPower assert person.fly() == "Flying..." assert !(person instanceof SupermanPower) } }
  • 64. class SupermanPower { String fly() { "Flying..." } } Mixins example class SpidermanPower { String spiderSense() { "Using spider-sense..." @Mixin([SpidermanPower]) class Person {} def person = new Person() assert person.spiderSense() == "Using spider-sense..." assert !(person instanceof SpidermanPower) Person.mixin SupermanPower assert person.fly() == "Flying..." assert !(person instanceof SupermanPower) } }
  • 65. class SupermanPower { String fly() { "Flying..." } } Mixins example class SpidermanPower { String spiderSense() { "Using spider-sense..." @Mixin([SpidermanPower]) class Person {} def person = new Person() assert person.spiderSense() == "Using spider-sense..." assert !(person instanceof SpidermanPower) Person.mixin SupermanPower assert person.fly() == "Flying..." assert !(person instanceof SupermanPower) } }
  • 66. Mixins example class SpidermanPower { String spiderSense() { "Using spider-sense..." @Mixin([SpidermanPower]) class Person {} def person = new Person() assert person.spiderSense() == "Using spider-sense..." assert !(person instanceof SpidermanPower) Person.mixin SupermanPower assert person.fly() == "Flying..." assert !(person instanceof SupermanPower) } } class SupermanPower { String fly() { "Flying..." } }
  • 67. Mixins example class SpidermanPower { String spiderSense() { "Using spider-sense..." @Mixin([SpidermanPower]) class Person {} def person = new Person() assert person.spiderSense() == "Using spider-sense..." assert !(person instanceof SpidermanPower) Person.mixin SupermanPower assert person.fly() == "Flying..." assert !(person instanceof SupermanPower) } } class SupermanPower { String fly() { "Flying..." } }
  • 68. Traits ▷ Groovy 2.3+ ▷ Similar to Java 8 default methods ▷ Supported in JDK 6, 7 and 8 ▷ Stateful ▷ Composition over inheritance ▷ Documentation
  • 69. Traits example trait SpidermanPower { String spiderSense() { "Using spider-sense..." class Person implements SpidermanPower {} def person = new Person() assert person.spiderSense() == "Using spider-sense..." assert person instanceof SpidermanPower def person2 = person.withTraits SupermanPower assert person2.fly() == "Flying..." assert person2 instanceof SupermanPower } } trait SupermanPower { String fly() { "Flying..." } }
  • 70. Traits example trait SpidermanPower { String spiderSense() { "Using spider-sense..." class Person implements SpidermanPower {} def person = new Person() assert person.spiderSense() == "Using spider-sense..." assert person instanceof SpidermanPower def person2 = person.withTraits SupermanPower assert person2.fly() == "Flying..." assert person2 instanceof SupermanPower } } trait SupermanPower { String fly() { "Flying..." } }
  • 71. Traits example trait SpidermanPower { String spiderSense() { "Using spider-sense..." class Person implements SpidermanPower {} def person = new Person() assert person.spiderSense() == "Using spider-sense..." assert person instanceof SpidermanPower def person2 = person.withTraits SupermanPower assert person2.fly() == "Flying..." assert person2 instanceof SupermanPower } } trait SupermanPower { String fly() { "Flying..." } }
  • 72. Traits example trait SpidermanPower { String spiderSense() { "Using spider-sense..." class Person implements SpidermanPower {} def person = new Person() assert person.spiderSense() == "Using spider-sense..." assert person instanceof SpidermanPower def person2 = person.withTraits SupermanPower assert person2.fly() == "Flying..." assert person2 instanceof SupermanPower } } trait SupermanPower { String fly() { "Flying..." } }
  • 74. MOP Method Synthesis ▷ Dynamically figure out behaviour upon invocation ▷ It may not exist until it's called/executed ▷ “Intercept, Cache, Invoke” pattern
  • 75. Check for methods and properties def p = new Person(name: 'Iván', age: 34) assert p.respondsTo('sayHi') assert p.respondsTo('sayHiTo', String) assert !p.respondsTo('goodbye') assert p.hasProperty('name') assert !p.hasProperty('country') class Person { String name Integer age String sayHi() { "Hi, my name is ${name} and I'm ${age}" } String sayHiTo(String name) { "Hi ${name}, how are you?" } }
  • 76. Check for methods and properties def p = new Person(name: 'Iván', age: 34) assert p.respondsTo('sayHi') assert p.respondsTo('sayHiTo', String) assert !p.respondsTo('goodbye') assert p.hasProperty('age') assert !p.hasProperty('country') class Person { String name Integer age String sayHi() { "Hi, my name is ${name} and I'm ${age}" } String sayHiTo(String name) { "Hi ${name}, how are you?" } }
  • 77. Check for methods and properties def p = new Person(name: 'Iván', age: 34) assert p.respondsTo('sayHi') assert p.respondsTo('sayHiTo', String) assert !p.respondsTo('goodbye') assert p.hasProperty('age') assert !p.hasProperty('country') class Person { String name Integer age String sayHi() { "Hi, my name is ${name} and I'm ${age}" } String sayHiTo(String name) { "Hi ${name}, how are you?" } }
  • 78. Check for methods and properties class Person { String name Integer age String sayHi() { "Hi, my name is ${name} and I'm ${age}" } String sayHiTo(String name) { "Hi ${name}, how are you?" } } def p = new Person(name: 'Iván', age: 34) assert p.respondsTo('sayHi') assert p.respondsTo('sayHiTo', String) assert !p.respondsTo('goodbye') assert p.hasProperty('age') assert !p.hasProperty('country')
  • 79. MethodMissing example ▷ Requirements: – Send notifications to users by different channels – +50 notifications – Not all notifications by all channels – Extensible and open to future modifications
  • 80. MethodMissing example abstract class Channel { void sendNewFollower(String username, String follower) { } void sendNewMessage(String username, String msg) { } ... } class EmailChannel extends Channel { void sendNewFollower(String username, String follower) { println "Sending email notification to '${username}' for new follower '${follower}'" } void sendNewMessage(String username, String msg) { println "Sending email notification to '${username}' for new message '${msg}'" } } class MobilePushChannel extends Channel { void sendNewFollower(String username, String follower) { println "Sending mobile push notification to '${username}' for new follower '${follower}'" } }
  • 81. MethodMissing example abstract class Channel { void sendNewFollower(String username, String follower) { } void sendNewMessage(String username, String msg) { } ... } class EmailChannel extends Channel { void sendNewFollower(String username, String follower) { println "Sending email notification to '${username}' for new follower '${follower}'" } void sendNewMessage(String username, String msg) { println "Sending email notification to '${username}' for new message '${msg}'" } } class MobilePushChannel extends Channel { void sendNewFollower(String username, String follower) { println "Sending mobile push notification to '${username}' for new follower '${follower}'" } }
  • 82. MethodMissing example abstract class Channel { void sendNewFollower(String username, String follower) { } void sendNewMessage(String username, String msg) { } ... } class EmailChannel extends Channel { void sendNewFollower(String username, String follower) { println "Sending email notification to '${username}' for new follower '${follower}'" } void sendNewMessage(String username, String msg) { println "Sending email notification to '${username}' for new message '${msg}'" } } class MobilePushChannel extends Channel { void sendNewFollower(String username, String follower) { println "Sending mobile push notification to '${username}' for new follower '${follower}'" } }
  • 83. MethodMissing example class NotificationService { List channels = [] def methodMissing(String name, args) { System.out.println "...methodMissing called for ${name} with args ${args}" // Generate the implementation def implementation = { Object[] methodArgs -> channels.each { channel -> def metaMethod = channel.metaClass.getMetaMethod(name, methodArgs) return metaMethod.invoke(channel, methodArgs) } } // Cache the implementation in the metaClass NotificationService instance = this instance.metaClass."$name" = implementation // Execute it! implementation(args) } }
  • 84. MethodMissing example class NotificationService { List channels = [] def methodMissing(String name, args) { System.out.println "...methodMissing called for ${name} with args ${args}" // Generate the implementation def implementation = { Object[] methodArgs -> channels.each { channel -> def metaMethod = channel.metaClass.getMetaMethod(name, methodArgs) return metaMethod.invoke(channel, methodArgs) } } // Cache the implementation in the metaClass NotificationService instance = this instance.metaClass."$name" = implementation // Execute it! implementation(args) } }
  • 85. MethodMissing example class NotificationService { List channels = [] def methodMissing(String name, args) { System.out.println "...methodMissing called for ${name} with args ${args}" // Generate the implementation def implementation = { Object[] methodArgs -> channels.each { channel -> def metaMethod = channel.metaClass.getMetaMethod(name, methodArgs) return metaMethod.invoke(channel, methodArgs) } } // Cache the implementation in the metaClass NotificationService instance = this instance.metaClass."$name" = implementation // Execute it! implementation(args) } } notificationService.sendNewFollower(...) notificationService.sendNewMessage(...)
  • 86. MethodMissing example class NotificationService { List channels = [] def methodMissing(String name, args) { System.out.println "...methodMissing called for ${name} with args ${args}" // Generate the implementation def implementation = { Object[] methodArgs -> channels.each { channel -> def metaMethod = channel.metaClass.getMetaMethod(name, methodArgs) return metaMethod.invoke(channel, methodArgs) } } // Cache the implementation in the metaClass NotificationService instance = this instance.metaClass."$name" = implementation // Execute it! implementation(args) } }
  • 87. MethodMissing example class NotificationService { List channels = [] def methodMissing(String name, args) { System.out.println "...methodMissing called for ${name} with args ${args}" // Generate the implementation def implementation = { Object[] methodArgs -> channels.each { channel -> def metaMethod = channel.metaClass.getMetaMethod(name, methodArgs) return metaMethod.invoke(channel, methodArgs) } } // Cache the implementation in the metaClass NotificationService instance = this instance.metaClass."$name" = implementation // Execute it! implementation(args) } }
  • 88. MethodMissing example def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()] ) assert !notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("John", "Peter") assert notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("Mary", "Steve") notificationService.sendNewMessage("Iván", "Hello!") // Execution ...methodMissing called for sendNewFollower with args [John, Peter] Sending email notification to 'John' for new follower 'Peter' Sending mobile push notification to 'John' for new follower 'Peter' Sending email notification to 'Mary' for new follower 'Steve' Sending mobile push notification to 'Mary' for new follower 'Steve' ...methodMissing called for sendNewMessage with args [Iván, Hello!] Sending email notification to 'Iván' for new message 'Hello!'
  • 89. MethodMissing example def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()] ) assert !notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("John", "Peter") assert notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("Mary", "Steve") notificationService.sendNewMessage("Iván", "Hello!") // Execution ...methodMissing called for sendNewFollower with args [John, Peter] Sending email notification to 'John' for new follower 'Peter' Sending mobile push notification to 'John' for new follower 'Peter' Sending email notification to 'Mary' for new follower 'Steve' Sending mobile push notification to 'Mary' for new follower 'Steve' ...methodMissing called for sendNewMessage with args [Iván, Hello!] Sending email notification to 'Iván' for new message 'Hello!'
  • 90. MethodMissing example def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()] ) assert !notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("John", "Peter") assert notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("Mary", "Steve") notificationService.sendNewMessage("Iván", "Hello!") // Execution ...methodMissing called for sendNewFollower with args [John, Peter] Sending email notification to 'John' for new follower 'Peter' Sending mobile push notification to 'John' for new follower 'Peter' Sending email notification to 'Mary' for new follower 'Steve' Sending mobile push notification to 'Mary' for new follower 'Steve' ...methodMissing called for sendNewMessage with args [Iván, Hello!] Sending email notification to 'Iván' for new message 'Hello!'
  • 91. MethodMissing example def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()] ) assert !notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("John", "Peter") assert notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("Mary", "Steve") notificationService.sendNewMessage("Iván", "Hello!") // Execution ...methodMissing called for sendNewFollower with args [John, Peter] Sending email notification to 'John' for new follower 'Peter' Sending mobile push notification to 'John' for new follower 'Peter' Sending email notification to 'Mary' for new follower 'Steve' Sending mobile push notification to 'Mary' for new follower 'Steve' ...methodMissing called for sendNewMessage with args [Iván, Hello!] Sending email notification to 'Iván' for new message 'Hello!'
  • 92. MethodMissing example def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()] ) assert !notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("John", "Peter") assert notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("Mary", "Steve") notificationService.sendNewMessage("class EmailChannel exItveánnd"s, C"hHaenlnleol! "{) void sendNewFollower(String username, String follower) {…} void sendNewMessage(String username, String msg) {…} // Execution ...} methodMissing called for sendNewFollower with args [John, Peter] Sending email notification to 'John' for new follower 'Peter' Sending class mobile MobilePushChannel push notification extends to Channel 'John' { for new follower 'Peter' void sendNewFollower(String username, String follower) {…} Sending } email notification to 'Mary' for new follower 'Steve' Sending mobile push notification to 'Mary' for new follower 'Steve' ...methodMissing called for sendNewMessage with args [Iván, Hello!] Sending email notification to 'Iván' for new message 'Hello!'
  • 93. MethodMissing example def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()] ) assert !notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("John", "Peter") assert notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("Mary", "Steve") notificationService.sendNewMessage("Iván", "Hello!") // Execution ...methodMissing called for sendNewFollower with args [John, Peter] Sending email notification to 'John' for new follower 'Peter' Sending mobile push notification to 'John' for new follower 'Peter' Sending email notification to 'Mary' for new follower 'Steve' Sending mobile push notification to 'Mary' for new follower 'Steve' ...methodMissing called for sendNewMessage with args [Iván, Hello!] Sending email notification to 'Iván' for new message 'Hello!'
  • 94. MethodMissing example def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()] ) assert !notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("John", "Peter") assert notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("Mary", "Steve") notificationService.sendNewMessage("Iván", "Hello!") // Execution ...methodMissing called for sendNewFollower with args [John, Peter] Sending email notification to 'John' for new follower 'Peter' Sending mobile push notification to 'John' for new follower 'Peter' Sending email notification to 'Mary' for new follower 'Steve' Sending mobile push notification to 'Mary' for new follower 'Steve' ...methodMissing called for sendNewMessage with args [Iván, Hello!] Sending email notification to 'Iván' for new message 'Hello!'
  • 95. MethodMissing example def notificationService = new NotificationService( channels: [new EmailChannel(), new MobilePushChannel()] ) assert !notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("John", "Peter") assert notificationService.respondsTo('sendNewFollower', String, String) notificationService.sendNewFollower("Mary", "Steve") notificationService.sendNewMessage("Iván", "Hello!") // Execution ...methodMissing called for sendNewFollower with args [John, Peter] Sending email notification to 'John' for new follower 'Peter' Sending mobile push notification to 'John' for new follower 'Peter' Sending email notification to 'Mary' for new follower 'Steve' Sending mobile push notification to 'Mary' for new follower 'Steve' ...methodMissing called for sendNewMessage with args [Iván, Hello!] Sending email notification to 'Iván' for new message 'Hello!'
  • 97. Compile-time metaprogramming ▷ Advance feature ▷ Analyze/modify program structure at compile time ▷ Cross-cutting features ▷ Write code that generates bytecode
  • 98. AST and compilation ▷ AST: Abstract Syntax Tree ▷ AST modified during compilation ▷ Hook into the phases ▷ Initialization, Parsing, Conversion, Semantic analysis, Canonicalization, Instruction selection, Class generation, Output, Finalization
  • 99. Groovy AST Transformations ▷ Lot of AST transformations out-of-the-box ▷ @EqualsAndHashCode, @ToString, @TuppleConstructor, @Canonical, @Grab, @Immutable, @Delegate, @Singleton, @Category, @Log4j, @CompileStatic, @TypeChecked, @Synchronized ...
  • 101. Global AST Transformations ▷ No annotation ▷ Meta-information file ▷ Applied to all code during compilation ▷ Any compilation phase ▷ Grails uses intensively in GORM
  • 103. Local AST Transformations ▷ Annotate code ▷ No meta-information file ▷ Easy to debug
  • 104. Steps to create local AST Interface AST Enjoy!
  • 105. Local AST example import geecon2014.Version @Version('1.0') class VersionedClass { } package geecon2014 import ... @Retention(RetentionPolicy.SOURCE) @Target([ElementType.TYPE]) @GroovyASTTransformationClass("geecon2014.VersionASTTransformation") @interface Version { String value() } class VersionedClass { public static final String VERSION = "1.0" }
  • 106. Local AST example import geecon2014.Version @Version('1.0') class VersionedClass { } package geecon2014 import ... @Retention(RetentionPolicy.SOURCE) @Target([ElementType.TYPE]) @GroovyASTTransformationClass("geecon2014.VersionASTTransformation") @interface Version { String value() } class VersionedClass { public static final String VERSION = "1.0" }
  • 107. Local AST example import geecon2014.Version @Version('1.0') class VersionedClass { } package geecon2014 import ... @Retention(RetentionPolicy.SOURCE) @Target([ElementType.TYPE]) @GroovyASTTransformationClass("geecon2014.VersionASTTransformation") @interface Version { String value() } class VersionedClass { public static final String VERSION = "1.0" }
  • 108. Local AST example @GroovyASTTransformation(phase = CompilePhase.SEMANTIC_ANALYSIS) class VersionASTTransformation extends AbstractASTTransformation { @Override public void visit(final ASTNode[] nodes, final SourceUnit source) { if (nodes.length != 2) { return } if (nodes[0] instanceof AnnotationNode && nodes[1] instanceof ClassNode) { def annotation = nodes[0] def version = annotation.getMember('value') if (version instanceof ConstantExpression) { nodes[1].addField('VERSION', ACC_PUBLIC | ACC_STATIC | ACC_FINAL, ClassHelper.STRING_TYPE, version) } else { source.addError(new SyntaxException("Invalid value for annotation", annotation.lineNumber, annotation.columnNumber)) } } } }
  • 109. Local AST example @GroovyASTTransformation(phase = CompilePhase.SEMANTIC_ANALYSIS) class VersionASTTransformation extends AbstractASTTransformation { @Override public void visit(final ASTNode[] nodes, final SourceUnit source) { if (nodes.length != 2) { return } if (nodes[0] instanceof AnnotationNode && nodes[1] instanceof ClassNode) { def annotation = nodes[0] def version = annotation.getMember('value') if (version instanceof ConstantExpression) { nodes[1].addField('VERSION', ACC_PUBLIC | ACC_STATIC | ACC_FINAL, ClassHelper.STRING_TYPE, version) } else { source.addError(new SyntaxException("Invalid value for annotation", annotation.lineNumber, annotation.columnNumber)) } } } }
  • 110. Local AST example // Execute with: // gradle build // groovy -cp build/libs/add-version-1.0.jar LocalASTExample.groovy import geecon.Version @Version('1.0') class VersionedClass { } println VersionedClass.VERSION // Execution 1.0
  • 111. Local AST example // Execute with: // gradle build // groovy -cp build/libs/add-version-1.0.jar LocalASTExample.groovy import geecon.Version @Version('1.0') class VersionedClass { } println VersionedClass.VERSION // Execution 1.0
  • 112. Local AST example // Execute with: // gradle build // groovy -cp build/libs/add-version-1.0.jar LocalASTExample.groovy import geecon.Version @Version('1.0') class VersionedClass { } println VersionedClass.VERSION // Execution 1.0
  • 113. 3. Recap Why we should use metaprogramming?
  • 114. Let’s review some concepts Metaprogramming out-of-the box Easy and very powerfull Write better code Add behaviour easily Take advantage of this power Because Groovy, it's groovy
  • 115. With great power comes great responsibility
  • 116. Thanks! Any questions? Iván López @ilopmar [email protected] https://github.com/lmivan http://kcy.me/1bzj7