前面Java 标注(Annotations)介绍 介绍了Java代码中Annotation的用法,使用Java Reflection API 也可以用来方法类,类成员或类方法的Annotation定义。
1.类Annotations
可以通过Class 的getAnnotations 来方法类的标注定义:
Class aClass = TheClass.class; Annotation[] annotations = aClass.getAnnotations(); for(Annotation annotation : annotations){ if(annotation instanceof MyAnnotation){ MyAnnotation myAnnotation = (MyAnnotation) annotation; System.out.println("name: " + myAnnotation.name()); System.out.println("value: " + myAnnotation.value()); } }
或者通过指定Annotation类型来访问类的标注:
Class aClass = TheClass.class; Annotation annotation = aClass.getAnnotation(MyAnnotation.class); if(annotation instanceof MyAnnotation){ MyAnnotation myAnnotation = (MyAnnotation) annotation; System.out.println("name: " + myAnnotation.name()); System.out.println("value: " + myAnnotation.value()); }
2. 类方法Annotations
类似的方法可以访问类方法的标注,如下例:
public class TheClass { @MyAnnotation(name="someName", value = "Hello World") public void doSomething(){} } ... Method method = ... //obtain method object Annotation[] annotations = method.getDeclaredAnnotations(); for(Annotation annotation : annotations){ if(annotation instanceof MyAnnotation){ MyAnnotation myAnnotation = (MyAnnotation) annotation; System.out.println("name: " + myAnnotation.name()); System.out.println("value: " + myAnnotation.value()); } }
或者指定Annotation类型:
Method method = ... // obtain method object Annotation annotation = method.getAnnotation(MyAnnotation.class); if(annotation instanceof MyAnnotation){ MyAnnotation myAnnotation = (MyAnnotation) annotation; System.out.println("name: " + myAnnotation.name()); System.out.println("value: " + myAnnotation.value()); }
3. 参数Annotations
访问参数的标注,如下例:
public class TheClass { public static void doSomethingElse( @MyAnnotation(name="aName", value="aValue") String parameter){ } } ... Method method = ... //obtain method object Annotation[][] parameterAnnotations = method.getParameterAnnotations(); Class[] parameterTypes = method.getParameterTypes(); int i=0; for(Annotation[] annotations : parameterAnnotations){ Class parameterType = parameterTypes[i++]; for(Annotation annotation : annotations){ if(annotation instanceof MyAnnotation){ MyAnnotation myAnnotation = (MyAnnotation) annotation; System.out.println("param: " + parameterType.getName()); System.out.println("name : " + myAnnotation.name()); System.out.println("value: " + myAnnotation.value()); } } }
4. 类成员Annotation
访问类成员标注的例子如下:
public class TheClass { @MyAnnotation(name="someName", value = "Hello World") public String myField = null; } ... Field field = ... //obtain field object Annotation[] annotations = field.getDeclaredAnnotations(); for(Annotation annotation : annotations){ if(annotation instanceof MyAnnotation){ MyAnnotation myAnnotation = (MyAnnotation) annotation; System.out.println("name: " + myAnnotation.name()); System.out.println("value: " + myAnnotation.value()); } }
或者
Field field = ... // obtain method object Annotation annotation = field.getAnnotation(MyAnnotation.class); if(annotation instanceof MyAnnotation){ MyAnnotation myAnnotation = (MyAnnotation) annotation; System.out.println("name: " + myAnnotation.name()); System.out.println("value: " + myAnnotation.value()); }