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Anotações Java Além da Reflexão Wellington Costa Pereira

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Wellington Costa Pereira ● +4 anos de experiência ● Mestrando em Ciências da Computação (UECE) ● Programar é vida! ● Open source <3 ● Compartilhar conhecimento <3 Github: https://github.com/WellingtonCosta Linkedin: https://www.linkedin.com/in/wellingtoncosta128 Email: [email protected]

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Sem mais delongas...

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Anotações?

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Anotações Introduzida na versão 5 do Java, as anotações, ou Annotations, são uma forma de representar metadados que podem vir a serem interpretados por um compilador, visando realizar alguma ação a partir desses metadados. As annotations também podem servir como uma forma para substituição das tradicionais configurações baseadas em XML ou até mesmo para geração de arquivos, muitas vezes arquivos de código-fonte.

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Lombok @ToString @EqualsAndHashCode public class Pessoa { @Getter @Setter private Long id; @Getter @Setter private String nome; @Getter @Setter private String email; @Getter @Setter private String telefone; }

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JPA @Entity @Table(name = "tb_pessoa") public class Pessoa { @Id private Long id; @Column private String nome; @Column private String email; @Column private String telefone; }

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Spring @RestController @RequestMapping("/api/pessoas") public class PessoaController { @GetMapping public List listarTodos() { // … } }

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Butter Knife public class PessoaActivity extends Activity { @BindView(R.id.nome) TextView nome; @BindView(R.id.email) TextView email; @BindView(R.id.telefone) TextView telefone; @Override protected void onCreate(Bundle savedInstance) { // … ButterKnife.inject(this); } }

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Java 5

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Java 5

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Java 5 ● JSR 14: Generics ● JSR 175: Annotations ● JSR 201: ○ Autoboxing / Unboxing ○ Enumerations ○ Static Imports ○ Enhanced For Loops ● apt command-line tool ● Dentre outras funcionalidades bacanas!

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JSR 269 ● 6 meses após o lançamento do Java 5 ● “Pluggable Annotation Processing API” ● Google, Oracle, dentre outras organizações patrocinaram ● Simplificar e padronizar o processamento de anotações ● Agora o apt faz parte do javac

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Componentes

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Componentes ● Annotation ● Processor ● APT (Annotation Processing Tool) ● Annotated Elements

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Annotation

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@Target(ElementType.TYPE) @Retention(RetentionPolicy.SOURCE) public @interface HelloWorld { }

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@Target(ElementType.TYPE) @Retention(RetentionPolicy.SOURCE) public @interface HelloWorld { }

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@Target(ElementType.TYPE) @Retention(RetentionPolicy.SOURCE) public @interface HelloWorld { }

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@Target(ElementType.TYPE) @Retention(RetentionPolicy.SOURCE) public @interface HelloWorld { }

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Processor

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interface Processor { Set getSupportedOptions(); Set getSupportedAnnotationTypes(); SourceVersion getSupportedSourceVersion(); void init(ProcesssingEnvironment processingEnv); boolean process(Set annotations, RoundEnvironment env); Iterable getCompletions(Element element, AnnotationMirror annotation, ExecutableElement member, String userText); }

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interface Processor { Set getSupportedOptions(); Set getSupportedAnnotationTypes(); SourceVersion getSupportedSourceVersion(); void init(ProcesssingEnvironment processingEnv); boolean process(Set annotations, RoundEnvironment env); Iterable getCompletions(Element element, AnnotationMirror annotation, ExecutableElement member, String userText); }

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Processing Environment

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interface ProcessingEnvironment { Map getOptions(); SourceVersion getSourceVersion(); Locale getLocale(); Messager getMessager(); Filer getFiler(); Elements getElementUtils(); Types getTypeUtils(); }

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interface ProcessingEnvironment { Map getOptions(); SourceVersion getSourceVersion(); Locale getLocale(); Messager getMessager(); Filer getFiler(); Elements getElementUtils(); Types getTypeUtils(); }

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Elements? Types?

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Elements public class HelloClass implements Runnable { private final String name; public HelloClass(String name) { this.name = name; } @Override public void run() { System.out.println(“Hello, ” + name); } }

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public class HelloClass implements Runnable { TypeElement private final String name; public HelloClass(String name) { this.name = name; } @Override public void run() { System.out.println(“Hello, ” + name); } } Elements

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public class HelloClass implements Runnable { TypeElement private final String name; VariableElement public HelloClass(String name) { this.name = name; } @Override public void run() { System.out.println(“Hello, ” + name); } } Elements

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public class HelloClass implements Runnable { TypeElement private final String name; VariableElement public HelloClass(String name) { this.name = name; ExecutableElement } @Override public void run() { System.out.println(“Hello, ” + name); } } Elements

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public class HelloClass implements Runnable { TypeElement private final String name; VariableElement public HelloClass(String name) { this.name = name; ExecutableElement } @Override public void run() { System.out.println(“Hello, ” + name); ExecutableElement } } Elements

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public class HelloClass implements Runnable { private final String name; public HelloClass(String name) { this.name = name; } @Override public void run() { System.out.println(“Hello, ” + name); } } Types

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public class HelloClass implements Runnable { private final String name; public HelloClass(String name) { this.name = name; } @Override public void run() { System.out.println(“Hello, ” + name); } } Types

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public class HelloClass implements Runnable { private final String name; public HelloClass(String name) { this.name = name; } @Override public void run() { System.out.println(“Hello, ” + name); } } Types

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public class HelloClass implements Runnable { private final String name; public HelloClass(String name) { this.name = name; } @Override public void run() { System.out.println(“Hello, ” + name); } } Types

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public class HelloClass implements Runnable { private final String name; public HelloClass(String name) { this.name = name; } @Override public void run() { System.out.println(“Hello, ” + name); } } Types

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public class HelloClass implements Runnable { private final String name; public HelloClass(String name) { this.name = name; } @Override public void run() { System.out.println(“Hello, ” + name); } } Types

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Criando nosso Processor

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public class HelloWorldProcessor extends AbstractProcessor { }

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public class HelloWorldProcessor extends AbstractProcessor { @Override public SourceVersion getSupportedSourceVersion() { return SourceVersion.latestSupported(); } }

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public class HelloWorldProcessor extends AbstractProcessor { @Override public SourceVersion getSupportedSourceVersion() { return SourceVersion.latestSupported(); } @Override public Set getSupportedAnnotationTypes() { return Collections.singleton(HelloWorld.class.getName()); } }

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public class HelloWorldProcessor extends AbstractProcessor { @Override public SourceVersion getSupportedSourceVersion() { return SourceVersion.latestSupported(); } @Override public Set getSupportedAnnotationTypes() { return Collections.singleton(HelloWorld.class.getName()); } @Override public boolean process( Set annotations, RoundEnvironment env) { } }

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public class HelloWorldProcessor extends AbstractProcessor { // . . . @Override public boolean process( Set annotations, RoundEnvironment env) { } }

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public class HelloWorldProcessor extends AbstractProcessor { // . . . @Override public boolean process( Set annotations, RoundEnvironment env) { Set elements = env.getElementsAnnotatedWith(HelloWorld.class); } }

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public class HelloWorldProcessor extends AbstractProcessor { // . . . @Override public boolean process( Set annotations, RoundEnvironment env) { Set elements = env.getElementsAnnotatedWith(HelloWorld.class); for(Element element : elements) { System.out.println(element); } } }

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public class HelloWorldProcessor extends AbstractProcessor { // . . . @Override public boolean process( Set annotations, RoundEnvironment env) { Set elements = env.getElementsAnnotatedWith(HelloWorld.class); for(Element element : elements) { System.out.println(element); } return false; } }

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public class HelloWorldProcessor extends AbstractProcessor { @Override public SourceVersion getSupportedSourceVersion() { return SourceVersion.latestSupported(); } @Override public Set getSupportedAnnotationTypes() { return Collections.singleton(HelloWorld.class.getName()); } @Override public boolean process( Set annotations, RoundEnvironment env) { Set elements = env.getElementsAnnotatedWith(HelloWorld.class); for(Element element : elements) { System.out.println(element); } return false; } }

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Anotando um elemento

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@HelloWorld public class HelloWorldClass { // . . . }

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@HelloWorld public class HelloWorldClass { // . . . }

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@HelloWorld public class HelloWorldClass { // . . . }

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Execução

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● Acontece automaticamente quando javac é executado ● ServiceLoader se encarrega de encontrar e instanciar os Processor Execução

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● META-INF/services ● Nome do arquivo ○ javax.annotation.processing.Processor ● Cada linha do arquivo deve ter o nome completo de cada Processor ○ com.example.HelloWorldProcessor ServiceLoader

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Processing Rounds

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● Acontece em duas etapas ● A primeira etapa processa os elementos anotados ○ Novos arquivos de código fonte podem ser gerados ○ Os arquivos compilados tem como saída seus bytecodes ● A segunda etapa acontece para verificar se novos arquivos gerados ○ Os eventuais arquivos gerados são compilados e tem como saída os arquivos bytecode Processing Rounds

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Gerando nosso código

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public class HelloWorldProcessor extends AbstractProcessor { // . . . @Override public boolean process( Set annotations, RoundEnvironment env) { Set elements = env.getElementsAnnotatedWith(HelloWorld.class); for(Element element : elements) { // Analisar os atributos de ‘element’ // Gerar código a partir desses atributos } return false; } }

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@Override public boolean process( Set annotations, RoundEnvironment env) { return false; }

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@Override public boolean process( Set annotations, RoundEnvironment env) { List classesInfo = parseHelloWorldAnnotation(env); return false; }

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@Override public boolean process( Set annotations, RoundEnvironment env) { List classesInfo = parseHelloWorldAnnotation(env); return false; } List parseHelloWorldAnnotation(RoundEnvironment env) { // . . . }

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@Override public boolean process( Set annotations, RoundEnvironment env) { List classesInfo = parseHelloWorldAnnotation(env); for(ClassInfo classInfo : classesInfo) { generateHelloWorldCode(classInfo); } return false; } List parseHelloWorldAnnotation(RoundEnvironment env) { // . . . }

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@Override public boolean process( Set annotations, RoundEnvironment env) { List classesInfo = parseHelloWorldAnnotation(env); for(ClassInfo classInfo : classesInfo) { generateHelloWorldCode(classInfo); } return false; } List parseHelloWorldAnnotation(RoundEnvironment env) { // . . . } void generateHelloWorldCode(ClassInfo classInfo) { // . . . }

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Element

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Element

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Element ClassInfo package: “com.example” element: name: “FooHelloWorld”

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Element ClassInfo package: “com.example” element: name: “FooHelloWorld” Generated Class

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Usando algumas armas!

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● Google Auto Common ● Google Auto Service ● JavaPoet Usando algumas armas

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● Lembram? META-INF/services/javax.annotation.processing.Processor Google Auto Service

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● Lembram? META-INF/services/javax.annotation.processing.Processor ● AutoService gera esses arquivos através de anotações! Google Auto Service

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● Lembram? META-INF/services/javax.annotation.processing.Processor ● AutoService gera esses arquivos através de anotações! Google Auto Service public class HelloWorldProcessor extends AbstractProcessor { // . . . }

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● Lembram? META-INF/services/javax.annotation.processing.Processor ● AutoService gera esses arquivos através de anotações! Google Auto Service @AutoService(Processor.class) public class HelloWorldProcessor extends AbstractProcessor { // . . . }

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TypeSpec.classBuilder(“FooHelloWorld”) .addModifiers(PUBLIC) .addMethod( MethodSpec.constructorBuilder() .addStatement( “System.out.println($S)”, “Hello, world!” ).build(); ).build(); JavaPoet

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TypeSpec.classBuilder(“FooHelloWorld”) .addModifiers(PUBLIC) .addMethod( MethodSpec.constructorBuilder() .addStatement( “System.out.println($S)”, “Hello, world!” ).build(); ).build(); public class FooHelloWorld { FooHelloWorld() { System.out.println(“Hello, world!”); } } JavaPoet

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E agora?

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Perguntas?

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Obrigado!