Annotation processing and code gen
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The document discusses annotation processing and code generation. It describes using annotation processing to automatically generate retry logic for HTTP requests by creating a $$RetryStale interface with the same methods as the original interface but adding cache headers. The processing is done at compile time using the ProcessingEnvironment API to access elements, generate code with JavaPoet, and write the generated files. It recommends libraries like AutoService, Truth, and Compile testing to make annotation processors easier to write.
![service.listRepos("koji");
service =
Proxy.newProxyInstance(serviceClass.getClassLoader(),
new Class[] { serviceClass },
new RetryStaleHandler(restAdapter.create(
Class.forName(serviceClass.getName()
+ "$$RetryStale"))));
@Override
public Object invoke(Object proxy, Method
method, Object[] args) throws Throwable {
...
if(method isGet and canRetry) {
try & catch block
}
...
}
RetryStaleHandler.java](https://image.slidesharecdn.com/annotationcodegen-150530091956-lva1-app6892/85/Annotation-processing-and-code-gen-15-320.jpg)
![JavaPoet
package foo.bar;
public final class Foo {
public static void main(String[] args) {
System.out.println("Hello, JavaPoet!");
}
}](https://image.slidesharecdn.com/annotationcodegen-150530091956-lva1-app6892/85/Annotation-processing-and-code-gen-41-320.jpg)
![MethodSpec main = MethodSpec.methodBuilder("main")
.addModifiers(Modifier.PUBLIC, Modifier.STATIC)
.returns(Void.class)
.addParameter(String[].class, "args")
.addStatement("$T.out.println($S)", System.class,
"Hello, JavaPoet!")
.build();
TypeSpec helloWorld =
TypeSpec.classBuilder("HelloWorld")
.addModifiers(Modifier.PUBLIC, Modifier.FINAL)
.addMethod(main)
.build();
JavaFile javaFile =
JavaFile.builder("foo.bar", helloWorld).build();
javaFile.writeTo(System.out);](https://image.slidesharecdn.com/annotationcodegen-150530091956-lva1-app6892/85/Annotation-processing-and-code-gen-42-320.jpg)
Annotation processing and code gen
- 1. Annotation Processing & Code Gen @kojilin 2015/05/30@TWJUG
- 4. Kaif Android Client •Using REST client to fetch article and debates •Need stable connection
- 5. Kaif Android Client •Using REST client to fetch article and debates •Need stable connection •If not, stale data is better than no data •Local cache Database •Http cache response
- 6. Rest Http Client •Retrofit from Square •A type-safe REST client for Android and Java •http://square.github.io/retrofit/
- 7. public interface GitHubService { @GET("/users/{user}/repos") List<Repo> listRepos(@Path("user") String user); }
- 8. RestAdapter restAdapter = new RestAdapter.Builder() .setEndpoint("https://api.github.com") .build(); GitHubService service = restAdapter.create(GitHubService.class);
- 9. List<Repo> repos = service.listRepos("octocat");
- 10. Header @Headers("Cache-Control: max-stale=86400") @GET("/users/{user}/repos") List<Repo> listRepos$$RetryStale(@Path("user") String user);
- 11. How to retry ? try { // normal access } catch (Exception e) { // force local cache if network error }
- 12. How to retry ? try { service.listRepos("koji"); } catch (Exception e) { if (e instanceof RetrofitError && isNetworkError(e)) { service.listRepos$$RetryStale("koji"); } }
- 13. If we do it manually •Every service access need previous try & catch code. try { service.listRepos("koji"); } catch (Exception e) { if (e instanceof RetrofitError && isNetworkError(e)) { service.listRepos$$RetryStale("koji"); } }
- 14. If we do it manually •Every service access need previous try & catch code. •Using Proxy pattern
- 15. service.listRepos("koji"); service = Proxy.newProxyInstance(serviceClass.getClassLoader(), new Class[] { serviceClass }, new RetryStaleHandler(restAdapter.create( Class.forName(serviceClass.getName() + "$$RetryStale")))); @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { ... if(method isGet and canRetry) { try & catch block } ... } RetryStaleHandler.java
- 16. If we do it manually •Every service access need previous try & catch code. •Using Proxy pattern •Almost every GET method need $$RetryStale version.
- 17. public interface GitHubService { @GET("/users/{user}/repos") List<Repo> listRepos(@Path("user") String user); @GET("/users/{user}/repos") @Headers("Cache-Control: max-stale=86400") List<Repo> listRepos$$RetryStale(@Path("user") String user); @GET("/repos/{owner}/{repo}/contributors") List<Contributor> contributors(@Path("owner") String owner, @Path("repo") String repo); @GET("/repos/{owner}/{repo}/contributors") @Headers("Cache-Control: max-stale=86400") List<Contributor> contributors$$RetryStale(@Path("owner") String owner, @Path("repo") String repo); }
- 18. If we do it manually •Every service access need previous try & catch code. •Using Proxy pattern. •Almost every GET method need $$RetryStale. •Generating boilerplate code during build.
- 19. How ? •Scan all interface has @GET method. •Generate new interface has both non- cache and cache method.
- 20. When scan? •Compile time. •Annotation Processing. •Run time. •Reflection. •Slow and feedback at runtime •Do we know the concrete class we want to generate when we are writing ?
- 22. Generate bytecode •Can do more than what java source can. •Bytecode is difficult to read and write. •ASM •JarJar •Dexmaker for android
- 23. Generate .java •Readable and maintainable. •JavaPoet from Square •Successor of JavaWriter •https://github.com/square/javapoet
- 24. public interface GitHubService { @GET("/users/{user}/repos") List<Repo> listRepos(@Path("user") String user); @GET("/repos/{owner}/{repo}/contributors") List<Contributor> contributors(@Path("owner") String owner, @Path("repo") String repo); }
- 25. public interface GitHubService$$RetryStale { @GET("/users/{user}/repos") List<Repo> listRepos(@Path("user") String user); @GET("/users/{user}/repos") @Headers("Cache-Control: max-stale=86400") List<Repo> listRepos$$RetryStale(@Path("user") String user); @GET("/repos/{owner}/{repo}/contributors") List<Contributor> contributors(@Path("owner") String owner, @Path("repo") String repo); @GET("/repos/{owner}/{repo}/contributors") @Headers("Cache-Control: max-stale=86400") List<Contributor> contributors$$RetryStale(@Path("owner") String owner, @Path("repo") String repo); }
- 26. AutoValue @AutoValue public abstract class Foo { public abstract String name(); public abstract int age(); }
- 27. final class AutoValue_Foo extends Foo { private final String name; private final int age; AutoValue_Foo( String name, int age) { if (name == null) { throw new NullPointerException("Null name"); } this.name = name; this.age = age; } @Override public String name() { return name; } @Override public int age() { return age; } @Override public String toString() { return "Foo{" + "name=" + name + ", age=" + age + "}"; } @Override public boolean equals(Object o) { if (o == this) { return true; } if (o instanceof Foo) { Foo that = (Foo) o; return (this.name.equals(that.name())) && (this.age == that.age()); } return false; } @Override public int hashCode() { int h = 1; h *= 1000003; h ^= name.hashCode(); h *= 1000003; h ^= age; return h; } }
- 28. Butter Knife @InjectView(R.id.content) public TextView content; @InjectView(R.id.last_update_time) public TextView lastUpdateTime; @InjectView(R.id.vote_score) public TextView voteScore; @InjectView(R.id.debater_name) public TextView debaterName; @InjectView(R.id.debate_actions) public DebateActions debateActions; public DebateViewHolder(View itemView) { super(itemView); ButterKnife.inject(this, itemView); content.setOnTouchListener(new ClickableSpanTouchListener()); }
- 29. @Override public void inject(final Finder finder, final T target, Object source) { View view; view = finder.findRequiredView(source, 2131296343, "field 'content'"); target.content = finder.castView(view, 2131296343, "field 'content'"); view = finder.findRequiredView(source, 2131296375, "field 'lastUpdateTime'"); target.lastUpdateTime = finder.castView(view, 2131296375, "field 'lastUpdateTime'"); view = finder.findRequiredView(source, 2131296374, "field 'voteScore'"); target.voteScore = finder.castView(view, 2131296374, "field 'voteScore'"); view = finder.findRequiredView(source, 2131296373, "field 'debaterName'"); target.debaterName = finder.castView(view, 2131296373, "field 'debaterName'"); view = finder.findRequiredView(source, 2131296370, "field 'debateActions'"); target.debateActions = finder.castView(view, 2131296370, "field 'debateActions'"); } @Override public void reset(T target) { target.content = null; target.lastUpdateTime = null; target.voteScore = null; target.debaterName = null; target.debateActions = null; }
- 30. JPA metamodel @Entity public class Pet { @Id Long id; String name; }
- 31. @StaticMetaModel(Pet.class) public class Pet_ { public static volatile SingularAttribute<Person, Long> id; public static volatile SingularAttribute<Person, String> name; } CriteriaBuilder cb = em.getCriteriaBuilder(); CriteriaQuery<Order> cq = cb.createQuery(Pet.class); cq.where(cb.equal(itemNode.get(Pet_.id), 5)) .distinct(true);
- 32. Annotation Processing •JSR 269 •Pluggable Annotation Processing API •Run automatically when javac runs •Using ServiceLoader to find •META-INF/services/ javax.annotation.processing.Processor •Running inside JVM
- 33. @SupportedSourceVersion(...) @SupportedAnnotationTypes( "retrofit.http.GET") public class MyProcessor extends AbstractProcessor { @Override public synchronized void init(ProcessingEnvironment env){ } @Override public boolean process( Set<? extends TypeElement> annotations, RoundEnvironment env) { } }
- 34. @SupportedSourceVersion(...) @SupportedAnnotationTypes( "retrofit.http.GET") public class MyProcessor extends AbstractProcessor { @Override public synchronized void init(ProcessingEnvironment env){ } @Override public boolean process( Set<? extends TypeElement> annotations, RoundEnvironment env) { } }
- 35. @SupportedSourceVersion(...) @SupportedAnnotationTypes(...) public class MyProcessor extends AbstractProcessor { @Override public synchronized void init(ProcessingEnvironment env){ } @Override public boolean process( Set<? extends TypeElement> annotations, RoundEnvironment env) { } }
- 37. Elements package foo.bar; public class Foo { // Type Element String bar; // Variable Element public void hoge() { // Executable Element System.out.println("Hello!"); } }
- 38. Types package foo.bar; public class Foo { String bar; public void hoge() { System.out.println("Hello!"); } }
- 39. @SupportedSourceVersion(...) @SupportedAnnotationTypes(...) public class MyProcessor extends AbstractProcessor { @Override public synchronized void init(ProcessingEnvironment env){ } @Override public boolean process( Set<? extends TypeElement> annotations, RoundEnvironment env) { } }
- 40. @Override public boolean process( Set<? extends TypeElement> annotations, RoundEnvironment env) { Set<? extends Element> elements = env.getElementsAnnotatedWith(GET.cl ass); // generating code for elements }
- 41. JavaPoet package foo.bar; public final class Foo { public static void main(String[] args) { System.out.println("Hello, JavaPoet!"); } }
- 42. MethodSpec main = MethodSpec.methodBuilder("main") .addModifiers(Modifier.PUBLIC, Modifier.STATIC) .returns(Void.class) .addParameter(String[].class, "args") .addStatement("$T.out.println($S)", System.class, "Hello, JavaPoet!") .build(); TypeSpec helloWorld = TypeSpec.classBuilder("HelloWorld") .addModifiers(Modifier.PUBLIC, Modifier.FINAL) .addMethod(main) .build(); JavaFile javaFile = JavaFile.builder("foo.bar", helloWorld).build(); javaFile.writeTo(System.out);
- 43. Element to JavaPoet •AnnotationSpec#get •AnnotationMirror to AnnotationSpec •MethodSpect#overriding •Override MethodElement
- 44. public interface Foo$$RetryStale { @GET("/foo/{user}") List<Foo> foo(@Path("user") String user); @GET("/foo/{user}") @Headers("Cache-Control: max-stale=86400") List<Foo> foo$$RetryStale(@Path("user") String user); }
- 45. TypeSpec.Builder typeSpecBuilder = TypeSpec.interfaceBuilder( classElement.getSimpleName() + "$RetryStale") .addModifiers(Modifier.PUBLIC); Interface public interface Foo$$RetryStale
- 46. Method MethodSpec.Builder builder = MethodSpec.methodBuilder("foo$RetryStale"); builder.addModifiers(Modifier.ABSTRACT) .addModifiers(Modifier.PUBLIC); methodElement.getParameters().stream().map(variableElement -> { ParameterSpec.Builder parameterBuilder = ParameterSpec.builder(TypeName.get(variableElement.asType()), variableElement.getSimpleName().toString()); variableElement.getAnnotationMirrors().stream() .map(AnnotationSpecUtil::generate) .forEach(parameterBuilder::addAnnotation); return parameterBuilder.build(); }).forEach(builder::addParameter); List<Foo> foo(@Path("user") String user)
- 48. Convenient Libraries •Google Auto-Service •Truth •Making your tests and their error messages more readable and discoverable •Google Compile testing
- 49. AutoService @AutoService(Processor.class) public class MyProcessor extends AbstracProcessor { ... } •Generating META-INF/services/ javax.annotation.processing.Processor
- 50. Truth and Compile testing ASSERT.about(javaSources()) .that(ImmutableList.of(inputFile)) .processedWith(new MyProcessor()) .compilesWithoutError() .and() .generatesSources(outputFile);
- 51. References •ANNOTATION PROCESSING 101 http://hannesdorfmann.com/annotation-processing/ annotationprocessing101/ •Annotation Processing Boilerplate Destruction https://speakerdeck.com/jakewharton/annotation- processing-boilerplate-destruction-square-waterloo-2014