Annotation(jdk5.0注解)复习(转自http://3w_cnblogs_com/pepcod/)

package annotation.test;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
 * 定义注解 Test <br>
 * 为方便测试：注解目标为类 方法，属性及构造方法<br>
 * 注解中含有三个元素 id ,name和 gid;  <br>
 * id 元素 有默认值 0 <br>
 */
@Target({ElementType.TYPE,ElementType.METHOD,ElementType.FIELD,ElementType.CONSTRUCTOR})
@Retention(RetentionPolicy.RUNTIME)
//有四个元注解，一般这两个 就可以搞定了
public @interface TestA {
    String name() default "";  //不写的话默认为空，不报错
    int id() default ;
    Class<Long> gid();
}

 1 package annotation.test;
 2
 3 import java.util.HashMap;
 4 import java.util.Map;
 7 /**
 8  * 这个类专门用来测试注解使用
 9  */
10
11 @TestA(name="type",gid=Long.class)
12 // 使用了类注解
13 public class UserAnnotation {
16     @TestA(name="param",id=1,gid=Long.class) // 使用了类成员注解
17     private Integer age;
18
19     @TestA(name="construct",id=2,gid=Long.class)// 使用了构造方法注解
20     public UserAnnotation() {
22     }
23
24     @TestA(name="public method", id=3, gid=Long.class)// 使用了 public 方法注解
25     public void a() {
26         Map<String, String> m = new HashMap<String, String>(0);
27     }
28
29     @TestA(name="protected method", id=4, gid=Long.class)//protected 方法注解
30     protected void b() {
31         Map<String, String> m = new HashMap<String, String>(0);
32     }
33
34     @TestA(name="private method " , id = 5, gid=Long.class) // private 方法注解
35     private void c(){
36         Map<String, String> m = new HashMap<String, String>(0);
37     }
38
39     public void b(Integer a){
41     }
42 }

package annotation.test;

import java.lang.annotation.Annotation;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;

public class ParseAnnotation {

    /**
     * 简单打印出UserAnnotation 类中所使用到的类注解
     * 该方法只打印了 Type 类型的注解
     * @throws ClassNotFoundException
     */
    public static void parseTypeAnnotation() throws ClassNotFoundException{
        Class clazz = Class.forName("annotation.test.UserAnnotation");
        Annotation[] annotations = clazz.getAnnotations();
        for (Annotation annotation : annotations) {
            TestA testA = (TestA) annotation;
            System.out.println("type name = "+clazz.getName() + "  |  id = " + testA.id() + "  |  name = " + testA.name() + "  |  　　　　　　　　　　　　　　　　　　　　gid = " + testA.gid());
        }
    }

    /**
     * 简单打印出UserAnnotation 类中所使用到的方法注解
     * 该方法只打印了 Method 类型的注解
     * @throws ClassNotFoundException
     */
    public static void parseMethodAnnotation() throws ClassNotFoundException{
        Method[] methods = UserAnnotation.class.getDeclaredMethods();
        for (Method method : methods) {
             /*
             * 判断方法中是否有指定注解类型的注解
             */
            boolean hasAnnotation = method.isAnnotationPresent(TestA.class);
            if(hasAnnotation){
                TestA annotation = method.getAnnotation(TestA.class);
                System.out.println("method name = " + method.getName() + "  |  id = " +
                        annotation.id() + "  |  description = " + annotation.name() + "  |  gid = " + annotation.gid());
            }
        }
    }

    /**
     * 简单打印出UserAnnotation 类中所使用到的构造方法注解
     * 该方法只打印了 构造方法 类型的注解
     * @throws ClassNotFoundException
     */
    public static void parseConstructAnnotation()  throws ClassNotFoundException{
        Constructor[] constructors = UserAnnotation.class.getConstructors();
        for (Constructor constructor : constructors) {
            /*
             * 判断构造方法中是否有指定注解类型的注解
             */
            boolean hasAnnotation = constructor.isAnnotationPresent(TestA.class);
            if(hasAnnotation){
                 /*
                 * 根据注解类型返回方法的指定类型注解
                 */
                TestA annotation = (TestA) constructor.getAnnotation(TestA.class);
                System.out.println("constructor = " + constructor.getName()
                        + "   |   id = " + annotation.id() + "  |  description = "
                        + annotation.name() + "  |   gid= "+annotation.gid());
            }
        }
    }

    /**
     * 简单打印出UserAnnotation 类中所使用到的字段注解
     * 该方法只打印了 Method 类型的注解
     * @throws ClassNotFoundException
     */
    public static void parseFieldAnnotation() throws ClassNotFoundException{
        Field[] fields = UserAnnotation.class.getDeclaredFields();
        for (Field field : fields) {
            boolean hasAnnotation = field.isAnnotationPresent(TestA.class);
            if(hasAnnotation){
                TestA annotation = field.getAnnotation(TestA.class);
                System.out.println("Field = " + field.getName()
                        + "  |  id = " + annotation.id() + "  |  description = "
                        + annotation.name() + "  |  gid= "+annotation.gid());
            }
        }
    }

    public static void main(String[] args) throws ClassNotFoundException {
        System.out.println("------------------------------解析Type注解----------------------------------------------------------");
        parseTypeAnnotation();
        System.out.println("------------------------------解析Method注解-------------------------------------------------------");
        parseMethodAnnotation();
        System.out.println("------------------------------解析构造方法(Construct)注解------------------------------------------");
        parseConstructAnnotation();
        System.out.println("------------------------------解析字段(Field)注解-----------------------------------------------------");
        parseFieldAnnotation();
    }
}