java自定义注解(一)

以下为@Controller的源码

/*

 *Copyright 2002-2007 the original author or authors.

 *

 *Licensed under the Apache License, Version 2.0 (the "License");

 *you may not use this file except in compliance with the License.

 *You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 *Unless required by applicable law or agreed to in writing, software

 *distributed under the License is distributed on an "AS IS" BASIS,

 *WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 *See the License for the specific language governing permissions and

 *limitations under the License.

 */

 

package org.springframework.stereotype;

 

import java.lang.annotation.Documented;

import java.lang.annotation.ElementType;

import java.lang.annotation.Retention;

importjava.lang.annotation.RetentionPolicy;

import java.lang.annotation.Target;

 

/**

 *Indicates that an annotated class is a "Controller" (e.g. a webcontroller).

 *

 *<p>This annotation serves as a specialization of {@link Component@Component},

 *allowing for implementation classes to be autodetected through classpathscanning.

 * Itis typically used in combination with annotated handler methods based on the

 *{@link org.springframework.web.bind.annotation.RequestMapping} annotation.

 *

 *@author Arjen Poutsma

 *@author Juergen Hoeller

 *@since 2.5

 *@see Component

 *@see org.springframework.web.bind.annotation.RequestMapping

 *@see org.springframework.context.annotation.ClassPathBeanDefinitionScanner

 */

@Target({ElementType.TYPE})

@Retention(RetentionPolicy.RUNTIME)

@Documented

@Component

public @interface Controller {

 

         /**

          * The value may indicate a suggestion for alogical component name,

          * to be turned into a Spring bean in case ofan autodetected component.

          * @return the suggested component name, if any

          */

         Stringvalue() default "";

 

}

 

/*

*自定义注解

*/

@Target()

@Retention()

Public @interface Name {

         StringXXXName default "";

}

 

1.      @Target表示该注解用于什么地方，可能的ElementType参数包括：

ElementType.CONSTRUCTOR  构造器声明

ElementType.FIELD  域声明

ElementType.LOCAL_VARIABLE  局部变量声明

ElementType.METHOD  方法声明

ElementType.PACKAGE  包声明

ElementType.PARAMETER  参数声明

ElementType.TYPE  类，接口(包括注解类型)或enum声明

 

2.      @Retention表示在什么级别保存该注解信息。可选RetentionPolicy参数包括：

RetentionPolicy.SOURCE  注解将被编译器丢弃

RetentionPolicy.CLASS  注解在class文件中可用，但会被vm丢弃

RetentionPolicy.RUNTIME  vm讲在运行期也保留注释，因此可以通过反思机制读取注解信息

 

 

/*

* 元注解@Target,@Retention,@Documented,@Inherited

*

*     @Target 表示该注解用于什么地方，可能的ElemenetType 参数包括：

*         ElemenetType.CONSTRUCTOR 构造器声明

*         ElemenetType.FIELD 域声明（包括 enum 实例）

*         ElemenetType.LOCAL_VARIABLE 局部变量声明

*         ElemenetType.METHOD 方法声明

*         ElemenetType.PACKAGE 包声明

*         ElemenetType.PARAMETER 参数声明

*         ElemenetType.TYPE 类，接口（包括注解类型）或enum声明

*        

*     @Retention 表示在什么级别保存该注解信息。可选的 RetentionPolicy 参数包括：

*         RetentionPolicy.SOURCE 注解将被编译器丢弃

*         RetentionPolicy.CLASS 注解在class文件中可用，但会被VM丢弃

*         RetentionPolicy.RUNTIME VM将在运行期也保留注释，因此可以通过反射机制读取注解的信息。

*        

*     @Documented 将此注解包含在 javadoc 中

*    

*     @Inherited 允许子类继承父类中的注解

*   

*/  

 

 

example

/**

 * Copyright 2011 by ekupeng

 */

package annotationTest;

 

import java.lang.annotation.ElementType;

import java.lang.annotation.Retention;

import java.lang.annotation.RetentionPolicy;

import java.lang.annotation.Target;

 

/**

 * @author liuyuansheng

 * create date 2011-8-27 下午06:25:13

 */

@Target(ElementType.METHOD)

@Retention(RetentionPolicy.RUNTIME)

 

public @interface Own {

public int id() default 0;

public String description() default "no description";

}

 

/**

 * Copyright 2011 by ekupeng

 */

package annotationTest;

 

import java.lang.reflect.Method;

 

import ClassTest.Test;

 

 

/**

 * @author liuyuansheng

 * create date 2011-8-27 下午06:27:37

 */

public class Test_1 {

 

/**

* @param args

*/

@Own(id = 1,description = "hello method_1")

public void method_1() {

 

}

 

@Own(id = 2)

public void method_2() {

 

}

 

@Own(id = 3,description = "last method")

public void method_3() {

 

}

 

public static void main(String[] args) {

// TODO Auto-generated method stub

Method[] methods = Test_1.class.getDeclaredMethods();

for (Method method : methods) {

boolean hasAnnotation = method.isAnnotationPresent(Own.class);

if (hasAnnotation) {

Own annotation = method.getAnnotation(Own.class);

System.out.println("Test( method = " + method.getName()

+ " ,id = " + annotation.id() + ", description = "

+ annotation.description() + ")");

}

}

}

 

}

output：

Test( method = method_1 ,id = 1, description = hello method_1)

Test( method = method_2 ,id = 2, description = no description)

Test( method = method_3 ,id = 3, description = last method)