The document discusses annotation processing tools (APT). It begins by defining what an annotation is and how they are used. It then covers retention policies, how annotations can be accessed at runtime via reflection, and the Mirror API. The bulk of the document provides an example of creating a custom annotation processor for Android data binding. It demonstrates creating annotations, configuring a processor, processing annotation elements, and generating code. The key aspects covered are how to implement an annotation processor by extending AbstractProcessor and processing annotation elements in the RoundEnvironment.

1. Annotation Processing
Tools
101

2. Txus Ballesteros
@txusballesteros
Rubén Serrano
@akelael

3. Agenda
1. Annotation Processing Tool
2. Discusión
3. Caso práctico

4. ¿Qué es eso de APT?

5. public @interface DummyAnnotiation {}
Anotación

6. Retención
• Constructor
• Atributo
• Variable
• Método
• Parámetro
• Etc.
• Source
• Class
• Runtime
Objetivo

7. Anotación
@Retention(CLASS) @Target(FIELD)
public @interface InjectView {
int value();
}

8. Runtime
Class tiene la magia:
• getAnnotation(Class<T> annotationType)
• getAnnotations()
• getDeclaredAnnotations()
• isAnnotationPresent(Class<T> annotationType)

9. Mirror API
http://docs.oracle.com/javase/1.5.0/docs/guide/apt/mirror/overview-summary.html

10. Discusión

11. Caso Práctico

12. Android Transformer
https://github.com/txusballesteros/android-transformer

13. Creando Anotaciones
@Retention(RetentionPolicy.SOURCE)
@Target(ElementType.TYPE)
public @interface Mappable {
Class<?> with();
}

14. Creando Anotaciones
@Retention(RetentionPolicy.SOURCE)
@Target(ElementType.TYPE)
public @interface Mappable {
Class<?> with();
}

15. Configurando las Anotaciones
@Retention(RetentionPolicy.SOURCE)
@Target(ElementType.TYPE)
public @interface Mappable {
Class<?> with();
}

16. Configurando las Anotaciones
@Retention(RetentionPolicy.SOURCE)
@Target(ElementType.TYPE)
public @interface Mappable {
Class<?> with();
}

17. @SupportedSourceVersion(SourceVersion.RELEASE_7)
@SupportedAnnotationTypes({
"com.mobandme.android.transformer.compiler.Mapping",
"com.mobandme.android.transformer.compiler.Mappable",
"com.mobandme.android.transformer.compiler.Parse"
})
public class AnnotationsProcessor extends AbstractProcessor {
RoundEnvironment roundEnvironment;
Map<String, MapperInfo> mappersList;
@Override
public boolean process(Set<? extends TypeElement> annotations,
RoundEnvironment roundEnv) {
return true;
}
Creando el Procesador

18. @SupportedSourceVersion(SourceVersion.RELEASE_7)
@SupportedAnnotationTypes({
"com.mobandme.android.transformer.compiler.Mapping",
"com.mobandme.android.transformer.compiler.Mappable",
"com.mobandme.android.transformer.compiler.Parse"
})
public class AnnotationsProcessor extends AbstractProcessor {
RoundEnvironment roundEnvironment;
Map<String, MapperInfo> mappersList;
@Override
public boolean process(Set<? extends TypeElement> annotations,
RoundEnvironment roundEnv) {
return true;
}
Creando el Procesador

19. @SupportedSourceVersion(SourceVersion.RELEASE_7)
@SupportedAnnotationTypes({
"com.mobandme.android.transformer.compiler.Mapping",
"com.mobandme.android.transformer.compiler.Mappable",
"com.mobandme.android.transformer.compiler.Parse"
})
public class AnnotationsProcessor extends AbstractProcessor {
RoundEnvironment roundEnvironment;
Map<String, MapperInfo> mappersList;
@Override
public boolean process(Set<? extends TypeElement> annotations,
RoundEnvironment roundEnv) {
return true;
}
Configurando el Procesador

20. Implementando el Procesador
@SupportedSourceVersion(SourceVersion.RELEASE_7)
@SupportedAnnotationTypes({
"com.mobandme.android.transformer.compiler.Mapping",
"com.mobandme.android.transformer.compiler.Mappable",
"com.mobandme.android.transformer.compiler.Parse"
})
public class AnnotationsProcessor extends AbstractProcessor {
RoundEnvironment roundEnvironment;
Map<String, MapperInfo> mappersList;
@Override
public boolean process(Set<? extends TypeElement> annotations,
RoundEnvironment roundEnv) {
return true;
}

21. Implementando el Procesador
private void processMappedAnnotationElements() {
Set<? extends Element> elements =
roundEnvironment.getElementsAnnotatedWith(Mapped.class);
for (Element mappedElement : elements) {
if (mappedElement.getKind() == ElementKind.FIELD) {
Mapped mappedAnnotation =
mappedElement.getAnnotation(Mapped.class);
String toFieldName = mappedAnnotation.toField();
}
}
}

22. Implementando el Procesador
private void processMappedAnnotationElements() {
Set<? extends Element> elements =
roundEnvironment.getElementsAnnotatedWith(Mapped.class);
for (Element mappedElement : elements) {
if (mappedElement.getKind() == ElementKind.FIELD) {
Mapped mappedAnnotation =
mappedElement.getAnnotation(Mapped.class);
String toFieldName = mappedAnnotation.toField();
}
}
}

23. Implementando el Procesador
private void processMappedAnnotationElements() {
Set<? extends Element> elements =
roundEnvironment.getElementsAnnotatedWith(Mapped.class);
for (Element mappedElement : elements) {
if (mappedElement.getKind() == ElementKind.FIELD) {
Mapped mappedAnnotation =
mappedElement.getAnnotation(Mapped.class);
String toFieldName = mappedAnnotation.toField();
}
}
}

24. Implementando el Procesador
private void processMappedAnnotationElements() {
Set<? extends Element> elements =
roundEnvironment.getElementsAnnotatedWith(Mapped.class);
for (Element mappedElement : elements) {
if (mappedElement.getKind() == ElementKind.FIELD) {
Mapped mappedAnnotation =
mappedElement.getAnnotation(Mapped.class);
String toFieldName = mappedAnnotation.toField();
}
}
}

25. Generando el Código
JavaFileObject file =
processingEnv.getFiler().createSourceFile(name);
BufferedWriter buffer =
new BufferedWriter(file.openWriter());
//…
buffer.close();

26. Configurando el Entorno
com.mobandme.android.transformer.compiler.internal.AnnotationsProcessor

27. Configuración de Gradle para el Compilador
buildscript {
repositories {
maven {
url "https://oss.sonatype.org/content/repositories/snapshots/"
}
jcenter()
}
dependencies {
classpath 'com.jimdo.gradle:gradle-apt-plugin:0.5-SNAPSHOT'
}
}
apply plugin: 'java'
apply plugin: 'apt'

28. El resultado final

29. ¿Preguntas?