Spring AOP 中 advice 的四种类型 before after throwing advice around

Spring AOP(Aspect-oriented programming) 是用于切面编程，简单的来说：AOP相当于一个拦截器，去拦截一些处理，例如：当一个方法执行的时候，Spring 能够拦截正在执行的方法，在方法执行的前或者后增加额外的功能和处理。

在Spring AOP中支持4中类型的通知：

1：before advice 在方法执行前执行。

2：after returning advice 在方法执行后返回一个结果后执行。

3：after throwing advice 在方法执行过程中抛出异常的时候执行。

4：Around advice 在方法执行前后和抛出异常时执行，相当于综合了以上三种通知。

下面是一个简单的AOP advice 的例子：

首先给出一个简单的Spring 注入的例子，

定义一个Book类：

package com.myapp.core.aop.advice;

public class Book {
private  String  name;
private  String  url;
private   int    pages;

public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
public int getPages() {
return pages;
}
public void setPages(int pages) {
this.pages = pages;
}

public  void  printName(){
System.out.println("Book name "+ this.name);
}

public  void  printUrl(){
System.out.println("Book URL "+this.url);
}

public  void  printThrowException(){
throw  new  IllegalArgumentException();
}

}

相应的配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> 
<!-- more bean definitions for data access objects go here -->

<bean id="book" class="com.myapp.core.aop.advice.Book">
<property name="name" value="Effective java" />
<property name="url" value="www.google.cn"/>
<property name="pages" value="300" />
</bean>
</beans>

对应的测试类：

package com.myapp.core.aop.advice;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainTest {
public static void main(String[] args) {

ApplicationContext  context  = new  ClassPathXmlApplicationContext("resource/aop.xml");

Book   book  =   (Book) context.getBean("book");

System.out.println("---------------------");

book.printName();

System.out.println("---------------------");

book.printUrl();

System.out.println("----------------------");

try{

book.printThrowException();

}catch(Exception e){
//  e.printStackTrace();
}

}
}

输出结果：

三月 20, 2013 11:01:01 上午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@11e831: startup date [Wed Mar 20 11:01:01 CST 2013]; root of context hierarchy
三月 20, 2013 11:01:01 上午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [resource/aop.xml]
三月 20, 2013 11:01:01 上午 org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@13b5500: defining beans [book]; root of factory hierarchy
---------------------
Book name Effective java
---------------------
Book URL www.google.cn
----------------------

下面对以上的Book加上Spring AOP advices

1：before advice

before advice将在方法执行前执行，创建一个实现MethodBeforeAdvice接口的类能够定义执行方法前的操作。
类如下：

package com.myapp.core.aop.advice;

import java.lang.reflect.Method;

import org.springframework.aop.MethodBeforeAdvice;

public class BeforeMethod  implements MethodBeforeAdvice {

@Override
public void before(Method arg0, Object[] arg1, Object arg2)
throws Throwable {
// TODO Auto-generated method stub

System.out.println("Before  Method");
System.out.println("--------------------");

}

}

配置对应的bean：
在aop.xml中配置，创建一个BeforeMethod类，一个新的代理命名为：bookProxy
1： target 设置你想拦截的bean
2：interceptorNames设置通知，你想作用于proxy/target上的
对应的配置文件如下：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> 
<!-- more bean definitions for data access objects go here -->

<bean id="book" class="com.myapp.core.aop.advice.Book">
<property name="name" value="Effective java" />
<property name="url" value="www.google.cn"/>
<property name="pages" value="300" />
</bean>

<bean id="beforeMethodBean" class="com.myapp.core.aop.advice.BeforeMethod" />

<bean id="bookProxy" class="org.springframework.aop.framework.ProxyFactoryBean">

<property name="target" ref="book"/>

<property name="interceptorNames">
<list>
<value>beforeMethodBean</value>
</list>
</property>

</bean>
</beans>

注意：为了使用proxy（代理）我们需要引入 CGLIB2， pom.xml文件中注入如下：

<dependency>
<groupId>cglib</groupId>
<artifactId>cglib</artifactId>
<version>2.2.2</version>
</dependency>

运行测试类：

package com.myapp.core.aop.advice;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainTest {
public static void main(String[] args) {

ApplicationContext  context  = new  ClassPathXmlApplicationContext("resource/aop.xml");

Book   book  =   (Book) context.getBean("bookProxy");

System.out.println("---------------------");

book.printName();

System.out.println("---------------------");

book.printUrl();

System.out.println("----------------------");

try{

book.printThrowException();

}catch(Exception e){
//  e.printStackTrace();
}

}
}

注意以上获得的是代理bean；
运行结果如下：

三月 20, 2013 2:18:56 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@eb67e8: startup date [Wed Mar 20 14:18:55 CST 2013]; root of context hierarchy
三月 20, 2013 2:18:56 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [resource/aop.xml]
三月 20, 2013 2:18:57 下午 org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@157985: defining beans [book,beforeMethodBean,bookProxy]; root of factory hierarchy
---------------------
Before  Method
--------------------
Book name Effective java
---------------------
Before  Method
--------------------
Book URL www.google.cn
----------------------
Before  Method
--------------------

2： after advice

在方法运行返回结果后将执行这个 afterReturning方法，创建的这个类必须实现：AfterReturningAdvice接口

package com.myapp.core.aop.advice;

import java.lang.reflect.Method;

import org.springframework.aop.AfterReturningAdvice;

public class AfterMethod  implements  AfterReturningAdvice {

@Override
public void afterReturning(Object arg0, Method arg1, Object[] arg2,
Object arg3) throws Throwable {
// TODO Auto-generated method stub

System.out.println("-------------------");

System.out.println("After  method ");

}

}

xml配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> 
<!-- more bean definitions for data access objects go here -->

<bean id="book" class="com.myapp.core.aop.advice.Book">
<property name="name" value="Effective java" />
<property name="url" value="www.google.cn"/>
<property name="pages" value="300" />
</bean>

<bean id="beforeMethodBean" class="com.myapp.core.aop.advice.BeforeMethod" />

<bean id="afterMethodBean" class="com.myapp.core.aop.advice.AfterMethod" />

<bean id="bookProxy" class="org.springframework.aop.framework.ProxyFactoryBean">

<property name="target" ref="book"/>

<property name="interceptorNames">
<list>
<value>beforeMethodBean</value>
<value>afterMethodBean</value>
</list>
</property>

</bean>
</beans>

运行结果如下：

三月 20, 2013 2:22:19 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@eb67e8: startup date [Wed Mar 20 14:22:19 CST 2013]; root of context hierarchy
三月 20, 2013 2:22:19 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [resource/aop.xml]
三月 20, 2013 2:22:20 下午 org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@157985: defining beans [book,beforeMethodBean,afterMethodBean,bookProxy]; root of factory hierarchy
---------------------
Before  Method
--------------------
Book name Effective java
-------------------
After  method
---------------------
Before  Method
--------------------
Book URL www.google.cn
-------------------
After  method
----------------------
Before  Method
--------------------

3：after throwing advice

当方法执行抛出一个异常后，会执行这个方法，创建一个类实现：ThrowsAdvice接口，创建一个afterThrowing拦截：IllegalArgumentException异常。
类如下：

package com.myapp.core.aop.advice;

import org.springframework.aop.ThrowsAdvice;

public class ThrowException  implements ThrowsAdvice{

public  void  afterThrowing(IllegalArgumentException e)  throws  Throwable{
System.out.println("after Throwing  Exception");
}
}

xml中配置文件如下：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> 
<!-- more bean definitions for data access objects go here -->

<bean id="book" class="com.myapp.core.aop.advice.Book">
<property name="name" value="Effective java" />
<property name="url" value="www.google.cn"/>
<property name="pages" value="300" />
</bean>

<!-- before  advice -->
<bean id="beforeMethodBean" class="com.myapp.core.aop.advice.BeforeMethod" />

<!-- after  advice -->
<bean id="afterMethodBean" class="com.myapp.core.aop.advice.AfterMethod" />

<!-- throwing  advice -->

<bean id="throwException" class="com.myapp.core.aop.advice.ThrowException" />

<bean id="bookProxy" class="org.springframework.aop.framework.ProxyFactoryBean">

<property name="target" ref="book"/>

<property name="interceptorNames">
<list>
<value>beforeMethodBean</value>
<value>afterMethodBean</value>
<value>throwException</value>
</list>
</property>

</bean>
</beans>

执行结果如下：

三月 20, 2013 2:37:36 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@eb67e8: startup date [Wed Mar 20 14:37:36 CST 2013]; root of context hierarchy
三月 20, 2013 2:37:36 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [resource/aop.xml]
三月 20, 2013 2:37:36 下午 org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@157985: defining beans [book,beforeMethodBean,afterMethodBean,throwException,bookProxy]; root of factory hierarchy
---------------------
Before  Method
--------------------
Book name Effective java
-------------------
After  method
---------------------
Before  Method
--------------------
Book URL www.google.cn
-------------------
After  method
----------------------
Before  Method
--------------------
after Throwing  Exception

4：Around advice

这个advice 联合了上面的三个advices，在方法执行期间执行，创建一个类实现MethodInterceptor接口，需要在方法中执行Object result = methodInvocation.proceed();方法才能得到执行，否则方法不会执行。
类如下：

package com.myapp.core.aop.advice;

import java.util.Arrays;

import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;

public class AroundMethod  implements MethodInterceptor{

@Override
public Object invoke(MethodInvocation methodInvocation) throws Throwable {
// TODO Auto-generated method stub

System.out.println("method  name:" + methodInvocation.getMethod().getName());

System.out.println("method  arguments" + Arrays.toString(methodInvocation.getArguments()));

System.out.println("Around  method : before ");

try{

Object result = methodInvocation.proceed();

System.out.println("Around method : after ");
return  result;

}catch(IllegalArgumentException e){

System.out.println("Around method : throw  an  exception ");
throw  e;
}
}

}

配置文件如下：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> 
<!-- more bean definitions for data access objects go here -->

<bean id="book" class="com.myapp.core.aop.advice.Book">
<property name="name" value="Effective java" />
<property name="url" value="www.google.cn"/>
<property name="pages" value="300" />
</bean>

<bean id="aroundMethod"  class="com.myapp.core.aop.advice.AroundMethod" />

<bean id="bookProxy" class="org.springframework.aop.framework.ProxyFactoryBean" >
<property name="target" ref="book"/>

<property name="interceptorNames">
<list>

<value>aroundMethod</value>
</list>
</property>

</bean>
</beans>

测试结果：

三月 20, 2013 3:02:19 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@eb67e8: startup date [Wed Mar 20 15:02:19 CST 2013]; root of context hierarchy
三月 20, 2013 3:02:19 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [resource/aop.xml]
三月 20, 2013 3:02:19 下午 org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@e29127: defining beans [book,aroundMethod,bookProxy]; root of factory hierarchy
---------------------
method  name:printName
method  arguments[]
Around  method : before
Book name Effective java
Around method : after
---------------------
method  name:printUrl
method  arguments[]
Around  method : before
Book URL www.google.cn
Around method : after
----------------------
method  name:printThrowException
method  arguments[]
Around  method : before
Around method : throw  an  exception

around advice得到实现。 over