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();
}
}

}
}
}
}