利用反射获取类或者方法或者字段上的注解的值

从JDK1.5之后，注解在各大框架上得到了广泛的应用。下面这个例子中，你可以判断一个类或者方法或者字段上有没有注解，以及怎么获取上面的注解值。话不多说，代码如下：
AnnotationTest01.java

package com.zkn.newlearn.annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE,ElementType.METHOD,ElementType.PARAMETER})
public @interface AnnotationTest01 {

    String color();
}

AnnotationTest02.java

package com.zkn.newlearn.annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface AnnotationTest02 {
    
    String getUserName();
}

AnnotationTest04.java

package com.zkn.newlearn.annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE,ElementType.FIELD})
public @interface AnnotationTest04 {
    
    String getAddress();
}

AnnotationTest03.java

package com.zkn.newlearn.annotation;

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

/**
 * 测试Annotation
 * @author zkn
 *
 */
@AnnotationTest02(getUserName="zhangsan")
public class AnnotationTest03 {

    @AnnotationTest01(color="red")
    public static String testColor(String color){
        System.out.println(color);
        return color;
    }
    
    @AnnotationTest04(getAddress="北京市海淀区")
    String address;
    
    public static void main(String[] args) {
        //获取方法上的注解值
        Method[] methods = AnnotationTest03.class.getDeclaredMethods();
        if(methods != null){
            for(Method method : methods){
                AnnotationTest01 annotation = method.getAnnotation(AnnotationTest01.class);
                if(annotation == null)
                    continue;
                Method[] me = annotation.annotationType().getDeclaredMethods();
                for(Method meth : me){
                    try {
                        String color = (String) meth.invoke(annotation,null);
                        System.out.println(color);
                    } catch (IllegalAccessException e) {
                        e.printStackTrace();
                    } catch (IllegalArgumentException e) {
                        e.printStackTrace();
                    } catch (InvocationTargetException e) {
                        e.printStackTrace();
                    }
                }
            }
        }

        //获取类上的注解值
        AnnotationTest02 anno = AnnotationTest03.class.getAnnotation(AnnotationTest02.class);
        if(anno != null){
            Method[] met = anno.annotationType().getDeclaredMethods();
            for(Method me : met ){
                if(!me.isAccessible()){
                    me.setAccessible(true);
                }
                try {
                    System.out.println(me.invoke(anno, null));
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                } catch (IllegalArgumentException e) {
                    e.printStackTrace();
                } catch (InvocationTargetException e) {
                    e.printStackTrace();
                }
            }
        }
        
        //获取字段上的注解值
        AnnotationTest03 noon = new AnnotationTest03();
        Field[] field = AnnotationTest03.class.getDeclaredFields();
        if(field != null){
            for(Field fie : field){
                if(!fie.isAccessible()){
                    fie.setAccessible(true);
                }
                AnnotationTest04 annon = fie.getAnnotation(AnnotationTest04.class);
                Method[] meth = annon.annotationType().getDeclaredMethods();
                for(Method me : meth){
                    if(!me.isAccessible()){
                        me.setAccessible(true);
                    }
                    try {
                        //给字段重新赋值
                        fie.set(noon, me.invoke(annon, null));
                        System.out.println(fie.get(noon));
                    } catch (IllegalAccessException e) {
                        e.printStackTrace();
                    } catch (IllegalArgumentException e) {
                        e.printStackTrace();
                    } catch (InvocationTargetException e) {
                        e.printStackTrace();
                    }
                }
                
            }
        }
    }
}