Marvel of Annotation Preprocessing in Java by Alexey Buzdin
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The document discusses various technologies and frameworks in Java, particularly focusing on annotation processing, dependency injection (Dagger), bean mapping (MapStruct), and code generation techniques. It highlights the practical applications of these technologies, their implementation details, and the performance implications of using reflection. Additionally, there are examples showcasing the use of annotations and libraries like Lombok to simplify Java code writing.
![@ToString
@ToString(exclude="id")
public class ToStringExample {
private static final int STATIC_VAR = 10;
private String name;
private Shape shape = new Square(5, 10);
private String[] tags;
private int id;
}](https://image.slidesharecdn.com/marvelofannotationinjava2-161106101424/85/Marvel-of-Annotation-Preprocessing-in-Java-by-Alexey-Buzdin-71-320.jpg)
![@EqualsAndHashCode
@EqualsAndHashCode(exclude={"id", "shape"})
public class EqualsAndHashCodeExample {
private transient int transientVar = 10;
private String name;
private double score;
private Shape shape = new Square(5, 10);
private String[] tags;
private int id;
}](https://image.slidesharecdn.com/marvelofannotationinjava2-161106101424/85/Marvel-of-Annotation-Preprocessing-in-Java-by-Alexey-Buzdin-72-320.jpg)
![@Data & @Value
@Data
public class PoJo {
private String name;
private double score;
private String[] tags;
private int id;
}
@Value
public class PoJo {
private String name;
private double score;
private String[] tags;
private int id;
}](https://image.slidesharecdn.com/marvelofannotationinjava2-161106101424/85/Marvel-of-Annotation-Preprocessing-in-Java-by-Alexey-Buzdin-74-320.jpg)
Marvel of Annotation Preprocessing in Java by Alexey Buzdin
- 1. Marvel of Annotation by Alexey Buzdin Preprocessing
- 3. ๏ What? ๏ Why? ๏ How? ๏ Dagger ๏ Lombok ๏ MapStruct ๏ Retrofit
- 4. ๏ What? ๏ Why? ๏ How? ๏ Dagger ๏ MapStruct ๏ Retrofit ๏ Lombok
- 5. “Developer loves to write code”
- 6. “Developer loves to write code” - noone ever
- 8. “Developer loves complex tasks” - probably you
- 10. CRUD
- 11. CRUD - api - type: XML, JSON - resources - /clients - access: R - entity 🔑 clientId - full name - email - /payments - entity 🔑 paymentId 🔑 clientId | link - amount - db: jdbc:mysql://localhost:3306/crudapp
- 12. CRUD - api - type: XML, JSON - resources - /clients - access: R - entity 🔑 clientId - full name - email - /payments - entity 🔑 paymentId 🔑 clientId | link - amount - db: jdbc:mysql://localhost:3306/crudapp Authentication?
- 13. CRUD - api - type: XML, JSON - resources - /clients - access: R - entity 🔑 clientId - full name - email - /payments - entity 🔑 paymentId 🔑 clientId | link - amount - db: jdbc:mysql://localhost:3306/crudapp - ldap: ldap://ldap.example.com/dc=example,dc=com
- 14. never let go of your D R E A M S
- 15. In Practice
- 16. In Practice Routing XML, JSON Building Response
- 17. public class SimpleServlet extends GenericServlet { public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException { // do something in here } } Generic Servlet
- 18. In Practice Routing XML, JSON Building Response
- 19. In Practice Map Validate Routing XML, JSON Building Response
- 20. In Practice Construct Query Map Validate Routing XML, JSON Building Response
- 21. Reflection and Runtime Code Generation Everywhere! Spring, Hibernate, GSON, Jersy, Dozer, Guice, Weld, etc…
- 23. Reflection - Slow? http://docs.oracle.com/javase/tutorial/reflect/index.html Performance Overhead Because reflection involves types that are dynamically resolved, certain Java virtual machine optimizations can not be performed. Consequently, reflective operations have slower performance than their non-reflective counterparts, and should be avoided in sections of code which are called frequently in performance-sensitive applications.
- 24. Reflection - Slow? http://docs.oracle.com/javase/tutorial/reflect/index.html Performance Overhead Because reflection involves types that are dynamically resolved, certain Java virtual machine optimizations can not be performed. Consequently, reflective operations have slower performance than their non-reflective counterparts, and should be avoided in sections of code which are called frequently in performance-sensitive applications.
- 25. Reflection - Slow? http://docs.oracle.com/javase/tutorial/reflect/index.html Performance Overhead Because reflection involves types that are dynamically resolved, certain Java virtual machine optimizations can not be performed. Consequently, reflective operations have slower performance than their non-reflective counterparts, and should be avoided in sections of code which are called frequently in performance-sensitive applications.
- 27. Code Generation? https://zeroturnaround.com/rebellabs/how-to-make-java-more-dynamic-with-runtime-code-generation/ Generates Java Bytecode at Runtime
- 28. Code Generation? https://zeroturnaround.com/rebellabs/how-to-make-java-more-dynamic-with-runtime-code-generation/ Generates Java Bytecode at Runtime Not always ok
- 29. Code Generation? https://zeroturnaround.com/rebellabs/how-to-make-java-more-dynamic-with-runtime-code-generation/ GWT, Android, j2objc, RoboVM, code transpilers Doesn’t work
- 31. Annotation Processing A tool build in javac for scanning and processing annotations at compile time
- 32. How? public class MyProcessor extends AbstractProcessor { @Override public synchronized void init(ProcessingEnvironment env){ } @Override public boolean process( Set<? extends TypeElement> annotations, RoundEnvironment env) { } @Override public Set<String> getSupportedAnnotationTypes() { } @Override public SourceVersion getSupportedSourceVersion() { } } http://hannesdorfmann.com/annotation-processing/annotationprocessing101/
- 33. How? public class MyProcessor extends AbstractProcessor { @Override public synchronized void init(ProcessingEnvironment env){ } @Override public boolean process( Set<? extends TypeElement> annotations, RoundEnvironment env) { } @Override public Set<String> getSupportedAnnotationTypes() { } @Override public SourceVersion getSupportedSourceVersion() { } } http://hannesdorfmann.com/annotation-processing/annotationprocessing101/
- 34. How? public class MyProcessor extends AbstractProcessor { @Override public synchronized void init(ProcessingEnvironment env){ } @Override public boolean process( Set<? extends TypeElement> annotations, RoundEnvironment env) { } @Override public Set<String> getSupportedAnnotationTypes() { } @Override public SourceVersion getSupportedSourceVersion() { } } http://hannesdorfmann.com/annotation-processing/annotationprocessing101/
- 35. How? public class MyProcessor extends AbstractProcessor { @Override public synchronized void init(ProcessingEnvironment env){ } @Override public boolean process( Set<? extends TypeElement> annotations, RoundEnvironment env) { } @Override public Set<String> getSupportedAnnotationTypes() { } @Override public SourceVersion getSupportedSourceVersion() { } } http://hannesdorfmann.com/annotation-processing/annotationprocessing101/
- 36. How? public class MyProcessor extends AbstractProcessor { @Override public synchronized void init(ProcessingEnvironment env){ } @Override public boolean process( Set<? extends TypeElement> annotations, RoundEnvironment env) { } @Override public Set<String> getSupportedAnnotationTypes() { } @Override public SourceVersion getSupportedSourceVersion() { } } http://hannesdorfmann.com/annotation-processing/annotationprocessing101/
- 37. How? MyProcessor.jar - com - example - MyProcessor.class - META-INF - services - javax.annotation.processing.Processor com.example.MyProcessor com.foo.OtherProcessor net.blabla.SpecialProcessor javax.annotation.processing.Processor javac will run the process in separate JVM
- 38. Example public class PizzaStore { public Meal order(String mealName) { if ("Margherita".equals(mealName)) return new MargheritaPizza(); if ("Calzone".equals(mealName)) return new CalzonePizza(); if ("Tiramisu".equals(mealName)) return new Tiramisu(); throw new IllegalArgumentException("Unknown meal '" + mealName + "'"); } }
- 39. Example public class PizzaStore { private MealFactory factory = new MealFactory(); public Meal order(String mealName) { return factory.create(mealName); } }
- 40. @Target(ElementType.TYPE) @Retention(RetentionPolicy.CLASS) public @interface Factory { Class type(); String id(); } @Factory( id = "Margherita", type = Meal.class ) public class MargheritaPizza implements Meal { @Override public float getPrice() { return 6f; } }
- 41. How? public class MyProcessor extends AbstractProcessor { @Override public synchronized void init(ProcessingEnvironment env){ } @Override public boolean process( Set<? extends TypeElement> annotations, RoundEnvironment env) { } @Override public Set<String> getSupportedAnnotationTypes() { } @Override public SourceVersion getSupportedSourceVersion() { } }
- 42. @Override public Set<String> getSupportedAnnotationTypes() { Set<String> annotataions = new LinkedHashSet<String>(); annotataions.add(Factory.class.getCanonicalName()); return annotataions; } @Override public SourceVersion getSupportedSourceVersion() { return SourceVersion.latestSupported(); }
- 43. @Override public synchronized void init(ProcessingEnvironment processingEnv) { super.init(processingEnv); typeUtils = processingEnv.getTypeUtils(); elementUtils = processingEnv.getElementUtils(); filer = processingEnv.getFiler(); messager = processingEnv.getMessager(); }
- 44. package com.example; // PackageElement public class Foo { // TypeElement private int a; // VariableElement private Foo other; // VariableElement public Foo () {} // ExecuteableElement public void setA ( // ExecuteableElement int newA // TypeElement ) {} }
- 45. @Override public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment env) { // Itearate over all @Factory annotated elements for (Element annotatedElement : env.getElementsAnnotatedWith(Factory.class)){ ... } }
- 46. @Override public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment env) { // Itearate over all @Factory annotated elements for (Element annotatedElement : env.getElementsAnnotatedWith(Factory.class)){ if (annotatedElement.getKind() != ElementKind.CLASS) { messager.printMessage(Diagnostic.Kind.ERROR, “Ooops!”, annotatedElement); return true; } ... } }
- 47. public class FactoryAnnotatedClass { private TypeElement annotatedClassElement;; private String simpleTypeName; // Class name private String id; // “Margherita” public FactoryAnnotatedClass(TypeElement classElement) throws Exception { Factory annotation = classElement.getAnnotation(Factory.class); … } }
- 48. try { Class<?> clazz = annotation.type(); qualifiedGroupClassName = clazz.getCanonicalName(); simpleFactoryGroupName = clazz.getSimpleName(); } catch (MirroredTypeException mte) { DeclaredType classTypeMirror = (DeclaredType) mte.getTypeMirror(); TypeElement classTypeElement = (TypeElement) classTypeMirror.asElement(); qualifiedGroupClassName = classTypeElement.getQualifiedName().toString(); simpleFactoryGroupName = classTypeElement.getSimpleName().toString(); }
- 49. public void generateCode(Elements elementUtils, Filer filer) throws IOException { MethodSpec.Builder method = MethodSpec.methodBuilder("create") .addModifiers(Modifier.PUBLIC) .addParameter(String.class, "id") .returns(TypeName.get(superClassName.asType())); // Foreach method.beginControlFlow("if ($S.equals(id))", item.getId()) .addStatement("return new $L()”, item.getTypeElement().getQualifiedName().toString()) .endControlFlow(); TypeSpec typeSpec = TypeSpec.classBuilder(factoryClassName) .addMethod(method.build()).build(); JavaFile.builder(packageName, typeSpec).build().writeTo(filer); } https://github.com/square/javapoet
- 51. Annotation Processing A tool build in javac for scanning and processing annotations at compile time
- 53. Dagger 2 The fastest Java DI Framework! https://google.github.io/dagger/
- 54. import javax.inject.Inject; class CoffeeMaker { @Inject Heater heater; @Inject Pump pump; ... } Dagger 2
- 55. @Component(modules = DripCoffeeModule.class) interface CoffeeShop { CoffeeMaker maker(); } @Module class DripCoffeeModule { @Provides static Heater provideHeater() { return new ElectricHeater(); } @Provides static Pump providePump(Thermosiphon pump) { return pump; } }
- 56. import javax.inject.Inject; class CoffeeMaker { @Inject Heater heater; @Inject Pump pump; ... } Dagger 2 CoffeeShop coffeeShop = DaggerCoffeeShop.create();
- 57. Dagger 2 ๏ Singletons and Scoped Bindings ๏ Lazy injections ๏ Provider injections ๏ Qualifiers
- 58. Dagger 2 The fastest Java DI Framework! https://google.github.io/dagger/
- 59. MapStruct Bean Mapping at Compile Time http://mapstruct.org/
- 60. public class Car { private String make; private int numberOfSeats; private CarType type; //constructor, getters, setters etc. }
- 61. @Mapper public interface CarMapper { CarMapper INSTANCE = Mappers.getMapper( CarMapper.class ); @Mappings({ @Mapping(source = "make", target = "manufacturer"), @Mapping(source = "numberOfSeats", target = "seatCount") }) CarDto carToCarDto(Car car); }
- 62. @Mapper public interface CarMapper { CarMapper INSTANCE = Mappers.getMapper( CarMapper.class ); @Mappings({ @Mapping(source = "make", target = "manufacturer"), @Mapping(source = "numberOfSeats", target = "seatCount") }) CarDto carToCarDto(Car car); }
- 63. @Mapper public interface CarMapper { CarMapper INSTANCE = Mappers.getMapper( CarMapper.class ); @Mappings({ @Mapping(source = "make", target = "manufacturer"), @Mapping(source = "numberOfSeats", target = "seatCount") }) CarDto carToCarDto(Car car); }
- 64. MapStruct http://mapstruct.org/ ๏ Nested mappings ๏ Updating existing bean instances
- 65. Retrofit A type-safe HTTP client for Java https://square.github.io/retrofit/
- 66. Retrofit public interface WeatherData { @GET(“weather?”) Observable<WeatherData> getWeatherData(@Query(“q”) String city); }
- 67. Retrofit retrofit = new Retrofit.Builder() .addCallAdapterFactory(RxJavaCallAdapterFactory.create()) .addConverterFactory(GsonConverterFactory.create()) .baseUrl("http://api.openweathermap.org/data/2.5/") .build(); WeatherService weatherService = retrofit.create(WeatherService.class); Observable<WeatherData> london = weatherService.getWeatherData("Riga");
- 68. Retrofit ๏ Header Manipulation ๏ Sync and Asyn calls ๏ Custom Converters
- 70. Lombok Spice up your Java https://projectlombok.org/
- 71. @ToString @ToString(exclude="id") public class ToStringExample { private static final int STATIC_VAR = 10; private String name; private Shape shape = new Square(5, 10); private String[] tags; private int id; }
- 72. @EqualsAndHashCode @EqualsAndHashCode(exclude={"id", "shape"}) public class EqualsAndHashCodeExample { private transient int transientVar = 10; private String name; private double score; private Shape shape = new Square(5, 10); private String[] tags; private int id; }
- 73. @RequiredArgsConstructor @RequiredArgsConstructor(staticName = "of") @AllArgsConstructor(access = AccessLevel.PROTECTED) public class ConstructorExample<T> { private int x, y; @NonNull private T description; @NoArgsConstructor public static class NoArgsExample { @NonNull private String field; } }
- 74. @Data & @Value @Data public class PoJo { private String name; private double score; private String[] tags; private int id; } @Value public class PoJo { private String name; private double score; private String[] tags; private int id; }
- 75. public String example() { val example = new ArrayList<String>(); example.add("Hello, World!"); val foo = example.get(0); return foo.toLowerCase(); }
- 76. public String example() { val example = new ArrayList<String>(); example.add("Hello, World!"); val foo = example.get(0); return foo.toLowerCase(); } val !!11one
- 77. @ExtensionMethod class Extensions { public static String toTitleCase(String in) { if (in.isEmpty()) return in; return "" + Character.toTitleCase(in.charAt(0)) + in.substring(1).toLowerCase(); } } @ExtensionMethod({java.util.Arrays.class, Extensions.class}) public class ExtensionMethodExample { public String test() { return "hELlO, WORlD!”.toTitleCase(); } }
- 79. Lombok Spice up your Java https://projectlombok.org/ ๏@Builder ๏@Log ๏@Delegate
- 85. Powerful Fast Sometimes a Life Saver Conclusion Powerful Fast Sometimes Brittle Annotation Processing
- 86. “Use it wisely we must!”