浅析Java自定义注解的用法

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.SOURCE)
public @interface Override {
}

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface AnnotationInfo {

    String[] value();

    int requestCode() default 0;
}

public class AnnotationExample {

    
    @AnnotationInfo(value = {"Android.permission.CALL_PHONE", "android.permission.CAMERA"}, requestCode = 10)
    public void requestPermission() {
        //其他逻辑
    }
}

public class AnnotationRuntimeProcessor {

    public static void main(String[] args) {
        try {
            //获取AnnotationExample的Class对象
            Class<?> cls = Class.forName("com.javastudy.Annotation.AnnotationExample");
            //获取AnnotationExample类中的方法
            Method[] methods = cls.getDeclaredMethods();
            for (Method method : methods) {
                //过滤不含自定义注解AnnotationInfo的方法
                boolean isHasAnnotation = method.isAnnotationPresent(AnnotationInfo.class);
                if (isHasAnnotation) {
                    method.setAccessible(true);
                    //获取方法上的注解
                    AnnotationInfo aInfo = method.getAnnotation(AnnotationInfo.class);
                    if (aInfo == null) return;
                    //解析注解上对应的信息
                    String[] permissions = aInfo.value();
                    System.out.println("value: " + Arrays.toString(permissions));

                    int requestCode = aInfo.requestCode();
                    System.out.println("requestCode: " + requestCode);
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

public class ProcessorExample extends AbstractProcessor {

    @Override
    public synchronized void init(ProcessingEnvironment processingEnvironment) {
        //processingEnvironment提供各种工具类  如Elements Filer Types SourceVersion等
        super.init(processingEnvironment);
    }

    
    @Override
    public boolean process(Set<? extends TypeElement> set, RoundEnvironment roundEnvironment) {
        return false;
    }

    @Override
    public SourceVersion getSupportedSourceVersion() {
        return super.getSupportedSourceVersion();
    }

    @Override
    public Set<String> getSupportedAnnotationTypes() {
        return super.getSupportedAnnotationTypes();
    }
}

@Retention(RetentionPolicy.CLASS)
@Target(ElementType.FIELD)
public @interface CompileAnnotation {

    int value() default 0;
}

@SupportedSourceVersion(SourceVersion.RELEASE_7)
@SupportedAnnotationTypes("com.suyun.aopermission.annotation.CompileAnnotation")
public class AnnotationCompileProcessor extends AbstractProcessor {

    private Messager messager;
    private Filer filer;

    @Override
    public synchronized void init(ProcessingEnvironment processingEnvironment) {
        //processingEnvironment提供各种工具类  如Elements Filer Types SourceVersion等
        super.init(processingEnvironment);
        messager = processingEnv.getMessager();
        filer = processingEnv.getFiler();
    }

    
    @Override
    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnvironment) {

        messager.printMessage(Diagnostic.Kind.NOTE, "----------start----------");

        for (TypeElement annotation : annotations) {
            Set<? extends Element> elements = roundEnvironment.getElementsAnnotatedWith(annotation);
            for (Element element : elements) {
                if (element.getKind() != ElementKind.FIELD) {
                    messager.printMessage(Diagnostic.Kind.ERROR, "Only FIELD can be annotated with AnnotationInfo");
                    return true;
                }
                //获取注解
                CompileAnnotation annotationInfo = element.getAnnotation(CompileAnnotation.class);
                //获取注解中的值
                int value = annotationInfo.value();
                messager.printMessage(Diagnostic.Kind.NOTE, "value: " + value);
            }
        }
        return true;
    }

}

public class MainActivity extends AppCompatActivity {

    @CompileAnnotation(value = 200)
    private TextView tv_text;
    
    //....省略其他代码....
}

com.suyun.aopermission.processor.AnnotationCompileProcessor

@AutoService(Processor.class)
public class AnnotationCompileProcessor extends AbstractProcessor {
//....其他逻辑....
}

try {
    //packageName是包名
    JavaFileObject source = mFiler.createSourceFile(packageName);
    Writer writer = source.openWriter();
    //classStr代表的类里所有的字符
    writer.write(classStr);
    writer.flush();
    writer.close();

} catch (Exception e) {
    e.printStackTrace();
}

                //创建method方法类
                MethodSpec methodSpec = MethodSpec.methodBuilder("getValue")
                        .addModifiers(Modifier.PUBLIC, Modifier.STATIC)
                        .returns(int.class)
                        .addStatement("return " + proAnnotation.value())
                        .build();
                //创建.class类
                TypeSpec typeSpec = TypeSpec.classBuilder("autoGenerate")
                        .addModifiers(Modifier.PUBLIC, Modifier.FINAL)
                        .addMethod(methodSpec)
                        .build();

                String packageName = processingEnv.getElementUtils().
                        getPackageOf(element).getQualifiedName().toString();
                try {
                    JavaFile javaFile = JavaFile.builder(packageName, typeSpec)
                            .addFileComment("this is auto generated")
                            .build();
                    javaFile.writeTo(filer);
                } catch (Exception e) {
                    e.printStackTrace();
                }

// this is auto generated
package org.ninetripods.MQ.javastudy;

public final class autoGenerate {
  public static int getValue() {
    return 100;
  }
}