Annotation Processing
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Annotation processing allows generating code at compile time by labeling code elements with annotations. It involves three main modules: a library module containing annotated code elements, a processor module containing the annotation processor, and an annotation module defining the annotations. The processor parses the annotated elements, allows accessing their properties, and can generate any code files. This allows automating boilerplate tasks like generating view holders for recycler views based on layout files annotated with adapter and view holder definitions.
![Attribute
@Target(METHOD)
@Retention(RUNTIME)
public @interface GET {
String value() default "";
}
@Retention(RUNTIME)
@Target(TYPE)
public @interface Component {
Class<?>[] modules() default {};
Class<?>[] dependencies() default {};
}](https://image.slidesharecdn.com/annotation-191201084044/85/Annotation-Processing-19-320.jpg)
![MethodSpec main = MethodSpec.methodBuilder("main")
.addParameter(String[].class, "args")
.build();
void main(String[] args) {
}
JavaPoet](https://image.slidesharecdn.com/annotation-191201084044/85/Annotation-Processing-49-320.jpg)
![MethodSpec main = MethodSpec.methodBuilder("main")
.addParameter(String[].class, "args")
.addStatement("$T.out.println($S)", System.class,
"Hello, JavaPoet!")
.build();
void main(String[] args) {
System.out.println("Hello, JavaPoet!");
}
JavaPoet](https://image.slidesharecdn.com/annotation-191201084044/85/Annotation-Processing-50-320.jpg)
![MethodSpec main = MethodSpec.methodBuilder("main")
.addParameter(String[].class, "args")
.addStatement("$T.out.println($S)", System.class,
“Hello, JavaPoet!")
.addModifiers(Modifier.PUBLIC, Modifier.STATIC)
.build();
public static void main(String[] args) {
System.out.println("Hello, JavaPoet!");
}
JavaPoet](https://image.slidesharecdn.com/annotation-191201084044/85/Annotation-Processing-51-320.jpg)
![TypeSpec helloWorld = TypeSpec.classBuilder("HellowWorld")
.addMethod(MethodSpec.{…})
.addModifiers(Modifier.PUBLIC, Modifier.FINAL)
.build();
public final class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, JavaPoet!");
}
}
JavaPoet](https://image.slidesharecdn.com/annotation-191201084044/85/Annotation-Processing-52-320.jpg)
Annotation Processing
- 2. About me Tim / Jintin Android / iOS developer Senior Software Engineer @ Carousell https://github.com/Jintin https://medium.com/@Jintin
- 3. How to write flawless code?
- 7. Don’t write ANY code
- 8. Do write LESS code
- 9. “Annotation Processing is a tool we can use to help us generate code in compile time by labeling Annotations inside our source code.”
- 10. Pros & Cons + Less boilerplate code + No Runtime Error - Block incremental build - Kotlin 1.3.30+ - Gradle 4.7+ - Compile overhead
- 11. One more thing…
- 12. One more inch…
- 13. How does Annotation Processing work?
- 14. How we use it dependencies { implementation 'com.google.dagger:dagger:2.x' kapt ‘com.google.dagger:dagger-compiler:2.x' } kapt stands for Kotlin annotation processing tool
- 15. Module structure Library module (optional) Processor(compiler) module Annotation module
- 16. Annotation
- 18. Attribute @GET(“XXX_Value") Observable getAPI(); @Component(modules = { AModule.class, BModule.class, CModule.class}) public interface MyComponent {}
- 19. Attribute @Target(METHOD) @Retention(RUNTIME) public @interface GET { String value() default ""; } @Retention(RUNTIME) @Target(TYPE) public @interface Component { Class<?>[] modules() default {}; Class<?>[] dependencies() default {}; }
- 20. Attribute Primitive types (int, long, etc.) String Classes (Foo::class) Enums Other annotations Arrays of the types listed above.
- 22. Target @Retention(RetentionPolicy.RUNTIME) @Target(value={CONSTRUCTOR, FIELD, LOCAL_VARIABLE, METHOD, PACKAGE, PARAMETER, TYPE}) public @interface Deprecated {}
- 24. Retention @Target(ElementType.METHOD) @Retention(SOURCE) public @interface Override {} @Target({ METHOD, CONSTRUCTOR, FIELD }) @Retention(RUNTIME) public @interface Inject {}
- 25. Retention public enum RetentionPolicy { /* only exist before compile finish. */ SOURCE, /* recorded in the class file by the compiler but need not be retained by the VM at run time. */ CLASS, /* to be recorded in the class file and can be used at run time, so they may be read reflectively. */ RUNTIME }
- 26. Retention public enum RetentionPolicy { /* only exist before compile finish. */ SOURCE, /* recorded in the class file by the compiler but need not be retained by the VM at run time. */ CLASS, /* to be recorded in the class file and can be used at run time, so they may be read reflectively. */ RUNTIME }
- 27. Retention public enum RetentionPolicy { /* only exist before compile finish. */ SOURCE, /* recorded in the class file by the compiler but need not be retained by the VM at run time. */ CLASS, /* to be recorded in the class file and can be used at run time, so they may be read reflectively. */ RUNTIME }
- 28. Retention public enum RetentionPolicy { /* only exist before compile finish. */ SOURCE, /* recorded in the class file by the compiler but need not be retained by the VM at run time. */ CLASS, /* to be recorded in the class file and can be used at run time, so they may be read reflectively. */ RUNTIME }
- 29. Processor module Only used in compile phase. Not include in final Jar/Apk. Can contain several Processors.
- 30. Hook
- 31. AutoService Hook @AutoService(Processor::class) class AdapterProcessor : Processor() dependencies { implementation ‘com.google.auto.service:auto-service:1.X’ }
- 32. public interface Processor { /** Initializes with the processing environment. */ void init(ProcessingEnvironment processingEnv); /** Returns the target the annotation types to process. */ Set<String> getSupportedAnnotationTypes(); /** Processes a set of annotation on type elements. */ boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnv); … } Processor
- 33. public interface Processor { /** Initializes with the processing environment. */ void init(ProcessingEnvironment processingEnv); /** Returns the target the annotation types to process. */ Set<String> getSupportedAnnotationTypes(); /** Processes a set of annotation on type elements. */ boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnv); … } Processor
- 34. public interface Processor { /** Initializes with the processing environment. */ void init(ProcessingEnvironment processingEnv); /** Returns the target the annotation types to process. */ Set<String> getSupportedAnnotationTypes(); /** Processes a set of annotation on type elements. */ boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnv); … } Processor
- 35. public interface Processor { /** Initializes with the processing environment. */ void init(ProcessingEnvironment processingEnv); /** Returns the target the annotation types to process. */ Set<String> getSupportedAnnotationTypes(); /** Processes a set of annotation on type elements. */ boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnv); … } Processor
- 36. Element Unit of code element. - PackageElement: Package - TypeElement: Class, Interface - ExecutableElement: Method, Constructor
- 37. @Override public boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnv) { for (Element element : roundEnv.getElementsAnnotatedWith(MyAnnotation.class)) { if (element.getKind() != ElementKind.INTERFACE) { error("Only interface can be used with MyAnnotation", element); return true; } TypeElement typeElement = (TypeElement) element; typeElement.getInterfaces(); typeElement.getSuperclass(); typeElement.getSimpleName(); MyAnnotation anno = element.getAnnotation(MyAnnotation.class); /** Custom logic to build the relation graph and generate the file*/ } return true; }
- 38. @Override public boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnv) { for (Element element : roundEnv.getElementsAnnotatedWith(MyAnnotation.class)) { if (element.getKind() != ElementKind.INTERFACE) { error("Only interface can be used with MyAnnotation", element); return true; } TypeElement typeElement = (TypeElement) element; typeElement.getInterfaces(); typeElement.getSuperclass(); typeElement.getSimpleName(); MyAnnotation anno = element.getAnnotation(MyAnnotation.class); /** Custom logic to build the relation graph and generate the file*/ } return true; }
- 39. @Override public boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnv) { for (Element element : roundEnv.getElementsAnnotatedWith(MyAnnotation.class)) { if (element.getKind() != ElementKind.INTERFACE) { error("Only interface can be used with MyAnnotation", element); return true; } TypeElement typeElement = (TypeElement) element; typeElement.getInterfaces(); typeElement.getSuperclass(); typeElement.getSimpleName(); MyAnnotation anno = element.getAnnotation(MyAnnotation.class); /** Custom logic to build the relation graph and generate the file*/ } return true; }
- 40. @Override public boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnv) { for (Element element : roundEnv.getElementsAnnotatedWith(MyAnnotation.class)) { if (element.getKind() != ElementKind.INTERFACE) { error("Only interface can be used with MyAnnotation", element); return true; } TypeElement typeElement = (TypeElement) element; typeElement.getInterfaces(); typeElement.getSuperclass(); typeElement.getSimpleName(); MyAnnotation anno = element.getAnnotation(MyAnnotation.class); /** Custom logic to build the relation graph and generate the file*/ } return true; }
- 41. @Override public boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnv) { for (Element element : roundEnv.getElementsAnnotatedWith(MyAnnotation.class)) { if (element.getKind() != ElementKind.INTERFACE) { error("Only interface can be used with MyAnnotation", element); return true; } TypeElement typeElement = (TypeElement) element; typeElement.getInterfaces(); typeElement.getSuperclass(); typeElement.getSimpleName(); MyAnnotation anno = element.getAnnotation(MyAnnotation.class); /** Custom logic to build the relation graph and generate the file*/ } return true; }
- 42. How to create file?
- 43. Filer Get from ProcessingEnvironment Generate file under build folder
- 44. Filer @Override public synchronized void init(ProcessingEnvironment env) { super.init(env); filer = env.getFiler(); } @Override public boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnv) { … filer.createSourceFile(“NewFile", element); }
- 45. How to create code?
- 46. JavaPoet/KotlinPoet Provide simple API to generate Java/Kotlin file Both Square open source projects Over 8000 stars in total
- 47. MethodSpec main = MethodSpec.methodBuilder("main") .build(); JavaPoet
- 48. MethodSpec main = MethodSpec.methodBuilder("main") .build(); void main() { } JavaPoet
- 49. MethodSpec main = MethodSpec.methodBuilder("main") .addParameter(String[].class, "args") .build(); void main(String[] args) { } JavaPoet
- 50. MethodSpec main = MethodSpec.methodBuilder("main") .addParameter(String[].class, "args") .addStatement("$T.out.println($S)", System.class, "Hello, JavaPoet!") .build(); void main(String[] args) { System.out.println("Hello, JavaPoet!"); } JavaPoet
- 51. MethodSpec main = MethodSpec.methodBuilder("main") .addParameter(String[].class, "args") .addStatement("$T.out.println($S)", System.class, “Hello, JavaPoet!") .addModifiers(Modifier.PUBLIC, Modifier.STATIC) .build(); public static void main(String[] args) { System.out.println("Hello, JavaPoet!"); } JavaPoet
- 52. TypeSpec helloWorld = TypeSpec.classBuilder("HellowWorld") .addMethod(MethodSpec.{…}) .addModifiers(Modifier.PUBLIC, Modifier.FINAL) .build(); public final class HelloWorld { public static void main(String[] args) { System.out.println("Hello, JavaPoet!"); } } JavaPoet
- 53. Tips Find the boilerplate of daily work, eg: findViewById, dependency graph, deep link, etc. Find the pattern and define each component. Label each component with annotation. Create processor to generate code and link each component.
- 54. Example
- 55. Factory public interface Animal {} public class Cat implements Animal {} public class Dog implements Animal {} public final class AnimalFactory { public static Animal createAnimal(String type) { switch(type) { case "cat": return new Cat(); case "dog": return new Dog(); } throw new RuntimeException("not support type"); } }
- 56. Factory public interface Animal {} public class Cat implements Animal {} public class Dog implements Animal {} public final class AnimalFactory { public static Animal createAnimal(String type) { switch(type) { case "cat": return new Cat(); case "dog": return new Dog(); } throw new RuntimeException("not support type"); } }
- 57. Auto Generate? @AutoFactory public interface Animal {} @AutoElement(AnimalTags.CAT) public class Cat implements Animal {} @AutoElement(AnimalTags.DOG) public class Dog implements Animal {} // https://github.com/Jintin/AutoFactory
- 58. Example 2
- 59. 1 ViewHolder public class MyAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> { protected static final int TYPE_HOLDER1 = 1; @Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { switch (viewType) { case TYPE_HOLDER1: { return new Holder1(LayoutInflater.from(context).inflate(R.layout.view1, parent, false)); } default: throw new RuntimeException("Not support type" + viewType); } } }
- 60. Add ViewHolder public class MyAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> { protected static final int TYPE_HOLDER1 = 1; protected static final int TYPE_HOLDER2 = 2; @Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { switch (viewType) { case TYPE_HOLDER1: { return new Holder1(LayoutInflater.from(context).inflate(R.layout.view1, parent, false)); } case TYPE_HOLDER2: { return new Holder2(LayoutInflater.from(context).inflate(R.layout.view2, parent, false)); } default: throw new RuntimeException("Not support type" + viewType); } } }
- 61. Add more ViewHolder public class MyAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> { protected static final int TYPE_HOLDER1 = 1; protected static final int TYPE_HOLDER2 = 2; protected static final int TYPE_HOLDER3 = 3; @Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { switch (viewType) { case TYPE_HOLDER1: { return new Holder1(LayoutInflater.from(context).inflate(R.layout.view1, parent, false)); } case TYPE_HOLDER2: { return new Holder2(LayoutInflater.from(context).inflate(R.layout.view2, parent, false)); } case TYPE_HOLDER3: { return new Holder3(LayoutInflater.from(context).inflate(R.layout.view3, parent, false)); } default: throw new RuntimeException("Not support type" + viewType); } } }
- 62. Even more ViewHolders public class MyAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> { protected static final int TYPE_HOLDER1 = 1; protected static final int TYPE_HOLDER2 = 2; protected static final int TYPE_HOLDER3 = 3; protected static final int TYPE_HOLDER4 = 4; protected static final int TYPE_HOLDER5 = 5; protected static final int TYPE_HOLDER6 = 6; @Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { switch (viewType) { case TYPE_HOLDER1: { return new Holder1(LayoutInflater.from(context).inflate(R.layout.view1, parent, false)); } case TYPE_HOLDER2: { return new Holder2(LayoutInflater.from(context).inflate(R.layout.view2, parent, false)); } case TYPE_HOLDER3: { return new Holder3(LayoutInflater.from(context).inflate(R.layout.view3, parent, false)); } case TYPE_HOLDER4: { return new Holder4(LayoutInflater.from(context).inflate(R.layout.view4, parent, false)); } case TYPE_HOLDER5: { return new Holder5(LayoutInflater.from(context).inflate(R.layout.view5, parent, false)); } case TYPE_HOLDER6: { return new Holder6(LayoutInflater.from(context).inflate(R.layout.view6, parent, false)); } default: throw new RuntimeException("Not support type" + viewType); } } }
- 63. Even more Adapters public class MyAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> { protected static final int TYPE_HOLDER1 = 1; protected static final int TYPE_HOLDER2 = 2; protected static final int TYPE_HOLDER3 = 3; protected static final int TYPE_HOLDER4 = 4; protected static final int TYPE_HOLDER5 = 5; protected static final int TYPE_HOLDER6 = 6; @Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { switch (viewType) { case TYPE_HOLDER1: { return new Holder1(LayoutInflater.from(context).inflate(R.layout.view1, parent, false)); } case TYPE_HOLDER2: { return new Holder2(LayoutInflater.from(context).inflate(R.layout.view2, parent, false)); } case TYPE_HOLDER3: { return new Holder3(LayoutInflater.from(context).inflate(R.layout.view3, parent, false)); } case TYPE_HOLDER4: { return new Holder4(LayoutInflater.from(context).inflate(R.layout.view4, parent, false)); } case TYPE_HOLDER5: { return new Holder5(LayoutInflater.from(context).inflate(R.layout.view5, parent, false)); } case TYPE_HOLDER6: { return new Holder6(LayoutInflater.from(context).inflate(R.layout.view6, parent, false)); } default: throw new RuntimeException("Not support type" + viewType); } } } public class MyAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> { protected static final int TYPE_HOLDER1 = 1; protected static final int TYPE_HOLDER2 = 2; protected static final int TYPE_HOLDER3 = 3; protected static final int TYPE_HOLDER4 = 4; protected static final int TYPE_HOLDER5 = 5; protected static final int TYPE_HOLDER6 = 6; @Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { switch (viewType) { case TYPE_HOLDER1: { return new Holder1(LayoutInflater.from(context).inflate(R.layout.view1, parent, false)); } case TYPE_HOLDER2: { return new Holder2(LayoutInflater.from(context).inflate(R.layout.view2, parent, false)); } case TYPE_HOLDER3: { return new Holder3(LayoutInflater.from(context).inflate(R.layout.view3, parent, false)); } case TYPE_HOLDER4: { return new Holder4(LayoutInflater.from(context).inflate(R.layout.view4, parent, false)); } case TYPE_HOLDER5: { return new Holder5(LayoutInflater.from(context).inflate(R.layout.view5, parent, false)); } case TYPE_HOLDER6: { return new Holder6(LayoutInflater.from(context).inflate(R.layout.view6, parent, false)); } default: throw new RuntimeException("Not support type" + viewType); } } }
- 64. Annotation Processing @BindHolder(Holder1.class) @BindHolder(Holder2.class) @BindHolder(Holder3.class, R.layout.view3) @BindHolder(Holder4.class, R.layout.view4) public class MyAdapter extends MyAdapterHelper {} @BindLayout(R.layout.item_holder1) class ViewHolder1 extends RecyclerView.ViewHolder {} @BindLayout(R.layout.item_holder2) class ViewHolder2 extends RecyclerView.ViewHolder {} // https://github.com/Jintin/ComposeAdapter
- 67. Q&A