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Annotation Processing
Taku Semba
CyberAgent.Inc
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About Me
Taku Semba
TakuSemba
@takusemba
AbemaTV.Inc
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Annotation Processing
Generate .java files when you compile
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Annotation Processing
Generate .java files when you compile
Merits
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Annotation Processing
Generate .java files when you compile
Merits
ɾDo not need to write repeatedly
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Annotation Processing
Generate .java files when you compile
Merits
ɾDo not need to write repeatedly
ɾTrust the generated code
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Annotation Processing
Generate .java files when you compile
Merits
Components
ɾDo not need to write repeatedly
ɾTrust the generated code
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Annotation Processing
Generate .java files when you compile
Merits
Components
ɾDo not need to write repeatedly
ɾTrust the generated code
ɾAnnotation
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Annotation Processing
Generate .java files when you compile
Merits
Components
ɾDo not need to write repeatedly
ɾTrust the generated code
ɾAnnotation
ɾProcessor
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class User {
String name;
int age;
}
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public final class UserBuilder {
private String name;
private int age;
public UserBuilder name(String name) {
this.name = name;
return this;
}
….
public User build() {
User user = new User();
user.name = this.name;
user.age = this.age;
return target;
}
}
class User {
String name;
int age;
}
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class User {
String name;
int age;
}
User user = new UserBuilder()
.age(23)
.name("taku")
.build();
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@Buildable
class User {
@BuilderField
String name;
@BuilderField
int age;
}
User user = new UserBuilder()
.age(23)
.name("taku")
.build();
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// BuildField.java
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.SOURCE)
public @interface BuilderField {
}
// Buildable.java
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.SOURCE)
public @interface Buildable {
}
Annotation
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Processor
// BuilderProcessor.java
@Override
public synchronized void init(ProcessingEnvironment processingEnv) {
// implementation
}
@Override
public boolean process(Set extends TypeElement> annotations,
RoundEnvironment roundEnv) {
// implementation
}
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Processor
// BuilderProcessor.java
private Filer filer;
private Messager messager;
private Elements elements;
@Override
public synchronized void init(ProcessingEnvironment processingEnv) {
super.init(processingEnv);
this.messager = processingEnv.getMessager();
this.filer = processingEnv.getFiler();
this.elements = processingEnv.getElementUtils();
}
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Processor
// BuilderProcessor.java
@Override
public boolean process(Set extends TypeElement> annotations,
RoundEnvironment roundEnv) {
// implementation
}
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Javapoet
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Processor
FieldSpec fieldSpec = FieldSpec
.builder(String.class, ”name”, Modifier.PRIVATE)
.build();
private String name;
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Processor
MethodSpec methodSpec = MethodSpec
.methodBuilder(”name”)
.addModifiers(Modifier.PUBLIC)
.returns(User.class)
.addParameter(String.class, ”name”)
.addStatement("this.$N = $N", ”name”, ”name”)
.addStatement("return this")
.build();
public UserBuilder name(String name) {
this.name = name;
return this;
}
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Processor
TypeSpec classSpec = TypeSpec
.classBuilder(”UserBuilder”)
.addModifiers(Modifier.PUBLIC, Modifier.FINAL)
.addFields(fieldSpecs)
.addMethods(methodsSpecs)
.build();
public final class UserBuilder {
// fields and methods
}
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Processor
JavaFile file = JavaFile
.builder(builderClass.packageName(), classSpec)
.build();
try {
file.writeTo(filer);
} catch (IOException e) {
messager.printMessage(Diagnostic.Kind.ERROR,
"Failed to create file " + builderClass.packageName());
}
> app/build/generated/source/apt/debug/your/package/UserBuilder.java
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@Buildable
class User {
@BuilderField
String name;
@BuilderField
int age;
}
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@Buildable
class User {
@BuilderField
String name;
@BuilderField
int age;
}
public final class UserBuilder {
private String name;
private int age;
….
public User build() {
User user = new User();
user.name = this.name;
user.age = this.age;
return target;
}
}
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@Buildable
class User {
@BuilderField
String name;
@BuilderField
int age;
}
public final class UserBuilder {
private String name;
private int age;
….
public User build() {
User user = new User();
user.name = this.name;
user.age = this.age;
return target;
}
}
User user = new UserBuilder().age(23).name("taku").build();
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Sample Code
https://github.com/TakuSemba/AutoBuilder
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Annotation Processing
https://github.com/takusemba
https://twitter.com/takusemba