Java Annotation 说明

在Java 程序中，除了源程序之外，我们还会用到Javadoc 标签对类、方法或成员变量进行注释。JDK5.0 的注解可以看成是Javadoc 标签和Xdoclet 标签的延伸和发展。在JDK5.0 中我们可以自定义标签，并通过Java语言的反射机制获取类中标注的注解。

@Retention(RetentionPolicy.RUNTIME)	// 声明注解的保留期限
@Target(ElementType.METHOD)			// 可使用注解的目标类型
public @interface AnnoTest {		// 定义注解

	boolean value() default true;	// 声明注解成员
	
}

public class UseAnnotation {

	@AnnoTest(value = true)
	public void method1(String name) {
		System.out.println("method1 " + name);
	}
	
	@AnnoTest(value = false)
	public void method2(String name) {
		System.out.println("method2 " + name);
	}
}

public class AnnoClient {

	public static void main(String[] args) {
		
		Class<UseAnnotation> clazz = UseAnnotation.class;
		Method[] methods = clazz.getDeclaredMethods();
		
		for (Method method : methods) {
			AnnoTest at = method.getAnnotation(AnnoTest.class);
			if (at != null) {
				if (at.value()) {
					System.out.println(method.getName() + " need test.");
				} else {
					System.out.println(method.getName() + " do not need test.");
				}
			}
		}
	}

}

public enum RetentionPolicy {
    /**
     * Annotations are to be discarded by the compiler.
     */
    SOURCE,

    /**
     * Annotations are to be recorded in the class file by the compiler
     * but need not be retained by the VM at run time.  This is the default
     * behavior.
     */
    CLASS,

    /**
     * Annotations are to be recorded in the class file by the compiler and
     * retained by the VM at run time, so they may be read reflectively.
     *
     * @see java.lang.reflect.AnnotatedElement
     */
    RUNTIME
}

public enum ElementType {
    /** Class, interface (including annotation type), or enum declaration */
    TYPE,

    /** Field declaration (includes enum constants) */
    FIELD,

    /** Method declaration */
    METHOD,

    /** Parameter declaration */
    PARAMETER,

    /** Constructor declaration */
    CONSTRUCTOR,

    /** Local variable declaration */
    LOCAL_VARIABLE,

    /** Annotation type declaration */
    ANNOTATION_TYPE,

    /** Package declaration */
    PACKAGE
}