java8 新增的@Repeatable注解

    package com.github.jdk8.ebook.java8_recipes2nd_edition;


import java.lang.annotation.Annotation;  
import java.lang.annotation.ElementType;  
import java.lang.annotation.Repeatable;  
import java.lang.annotation.Retention;  
import java.lang.annotation.RetentionPolicy;  
import java.lang.annotation.Target;  
import java.util.Arrays;  


/** 
 * java8 新增的@Repeatable注解，其實只是語法糖而已． 
 * java8 注解的 {@link RepeatAnn} 類與 {@link Annotations}是等價的． 
 * 新注解講語法糖轉化為注解值為數組形式． 
 * @author doctor 
 * 
 * @since 2015年2月3日 下午8:33:43 
 */  
public class Chapter2Code {  

    public static void main(String[] args) {  
        Annotation[] annotations = RepeatAnn.class.getAnnotations();  
        System.out.println(annotations.length); //1  
        Arrays.stream(annotations).forEach(System.out::println);//@com.github.jdk8.ebook.java8_recipes2nd_edition.Chapter2Code$Roles(value=[@com.github.jdk8.ebook.java8_recipes2nd_edition.Chapter2Code$Role(name=doctor), @com.github.jdk8.ebook.java8_recipes2nd_edition.Chapter2Code$Role(name=who)])  

        Annotation[] annotations2 = Annotations.class.getAnnotations();  
        System.out.println(annotations2.length);//1  
        Arrays.stream(annotations2).forEach(System.out::println);//@com.github.jdk8.ebook.java8_recipes2nd_edition.Chapter2Code$Roles(value=[@com.github.jdk8.ebook.java8_recipes2nd_edition.Chapter2Code$Role(name=doctor), @com.github.jdk8.ebook.java8_recipes2nd_edition.Chapter2Code$Role(name=who)])  

    }  

    /** 
     * The same annotation can be applied to a declaration or type more than 
     * once, given that each annotation is marked as @Repeatable. In the 
     * following code, the @Repeatable annotation is used to develop an 
     * annotation that can be repeated, rather than grouped together as in 
     * previous releases of Java. In this situation, an annotation named Role is 
     * being created, and it will be used to signify a role for an annotated 
     * class or method. 
     *  
     * @author doctor 
     * 
     * @since 2015年2月3日 下午8:51:09 
     */  
    @Repeatable(value = Roles.class)  
    public static @interface Role {  
        String name() default "doctor";  
    }  

    @Target(ElementType.TYPE)  
    @Retention(RetentionPolicy.RUNTIME)  
    public static @interface Roles {  
        Role[] value();  
    }  

    @Role(name = "doctor")  
    @Role(name = "who")  
    public static class RepeatAnn{  

    }  

    @Roles({@Role(name="doctor"),  
            @Role(name="who")})  
    public static class Annotations{  

    }  
}  </pre><br />

來自：http://blog.csdn.net/doctor_who2004/article/details/43457689