spring aop

 一，从代理机制初探AOP
  1，使用静态代理

#代理对象和被代理对象必须实现共同的接口
package com.biaoflying;

public interface IHello {
    public void hello(String name);
}

 

#代理对象HelloProxy
package com.biaoflying;

import java.util.logging.*;

public class HelloProxy implements IHello {
    private IHello helloObject;
    private Logger logger=
        Logger.getLogger(this.getClass().getName());
    
    public HelloProxy(IHello helloObject){
        this.helloObject=helloObject;
    }
    public void hello(String name){
        log("hello method starts....");
        helloObject.hello(name);
        log("hello method ends....");
    }
    
    private void log(String msg){
        logger.log(Level.INFO,msg);
    }
}

 

#HelloSpeaker被代理对象
package com.biaoflying;

public class HelloSpeaker implements IHello {
    public void hello(String name){
        System.out.println("Hello "+name);
    }
}

 

#主程序
package com.biaoflying;

public class ProxyDemo {
    public static void main(String[] args){
        HelloProxy proxy=
            new HelloProxy(new HelloSpeaker());
        proxy.hello("biaoflying");
    }
}

 

#执行ProxyDemo的输出
信息: hello method starts....
Hello biaoflying
2008-3-21 9:05:40 com.biaoflying.HelloProxy log
信息: hello method ends....

  TIP:使用静态代理，代理对象和被代理对象必须实现共同的接口。本质上就是由代理对象呼叫被代理对象并执行相关的逻辑。同时可以看到，静态代理在程序规模稍大时就无法胜任了。

-----------------------------------------------------------------------------------

  2，动态代理

  去掉HelloProxy.java，编写以下的LogHandler.java文件。

package com.biaoflying;

import java.util.logging.*;
import java.lang.reflect.*;

public class LogHandler implements InvocationHandler{
    private Logger logger=
        Logger.getLogger(this.getClass().getName());
    
    private Object delegate;
    
    public Object bind(Object delegate){
        this.delegate=delegate;
        return Proxy.newProxyInstance(
                delegate.getClass().getClassLoader(),
                delegate.getClass().getInterfaces(),
                this);
    }
    public Object invoke(Object proxy,Method method,
            Object[] args)throws Throwable{
        Object result = null;
        try{
            log("method starts..."+method);
            result=method.invoke(delegate,args);
            logger.log(Level.INFO,"method ends..."+method);
        }catch(Exception e){
            log(e.toString());
        }
    return result;
    }
    private void log(String msg){
        logger.log(Level.INFO,msg);
}
}

 

#主程序
package com.biaoflying;

public class ProxyDemo2 {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        LogHandler logHandler=new LogHandler();
        IHello helloProxy=
            (IHello)logHandler.bind(new HelloSpeaker());
        helloProxy.hello("biaoflying");
    }
}

  TIP：动态代理的执行流程是Proxy.newProxyInstance(..,..,this)方法返回一个代理对象，该代理对象每次执行相关的方法时都会委托给this.invoke方法。

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  二，Advices

  由于织入Targets的时机不同，Advices被分为以下几种：Before advice,After advice,Around advice,Throw advice。

#MethodBeforeAdvice接口
package org.springframework.aop;
public interface MethodBeforeAdvice extends BeforeAdvice{
  void before(Method method,Object[] args,Object target)
  throws Throwable;
}

 
  具体的例子，IHello接口和HelloSpeaker.java如上

package com.biaoflying;

import java.lang.reflect.Method;
import java.util.logging.*;
import org.springframework.aop.MethodBeforeAdvice;

public class LogBeforeAdvice
        implements MethodBeforeAdvice{
    private Logger logger=
        Logger.getLogger(this.getClass().getName());
    
    public void before(Method method,Object[] args,
            Object target)throws Throwable{
        logger.log(Level.INFO,"Method starts..."+method);
    }
}

 

package com.biaoflying;

import org.springframework.context.*;
import org.springframework.context.support.*;

public class SpringAOPDemo {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        ApplicationContext context=
            new FileSystemXmlApplicationContext(
                    "beans-config.xml");
        IHello helloProxy=(IHello)context.getBean(
                "helloProxy");
        helloProxy.hello("biaoflying");
    }

}

 

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING/DTD BEAN/EN"
 "http://www.springframework.org/dtd/spring-beans.dtd">
 
<beans>
    <bean id="logBeforeAdvice"
        class="com.biaoflying.LogBeforeAdvice"/>
    <bean id="helloSpeaker"
        class="com.biaoflying.HelloSpeaker"/>
        
    <bean id="helloProxy"
        class="org.springframework.aop.framework.ProxyFactoryBean">
        <property name="proxyInterfaces">
            <value>com.biaoflying.IHello</value>
        </property>
        <property name="target">
            <ref bean="helloSpeaker"/>
        </property>
        <property name="interceptorNames">
            <list>
                <value>logBeforeAdvice</value>
            </list>
        </property>
    </bean>
</beans>

  执行SpringAOPDemo.java会在hello方法执行之前输出log消息。
  另外对于After advice,Around advice是类似的。

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  三，Throw Advice
 
  表示在目标对象调用方法发生异常时添加一个Aspect。

package com.biaoflying;

public interface IHello {
    public void hello(String name)throws Throwable;
}

 

package com.biaoflying;

public class HelloSpeaker implements IHello {
    public void hello(String name)throws Throwable{
        System.out.println("Hello "+name);
        throw new Exception("发生异常...");
    }
}

 

package com.biaoflying;

import java.lang.reflect.Method;
import java.util.logging.*;
import org.springframework.aop.ThrowsAdvice;

public class SomeThrowAdvice implements ThrowsAdvice{
    private Logger logger=
        Logger.getLogger(this.getClass().getName());
    public void afterThrowing(Method method,Object[] args,Object target,Throwable subclass){
        logger.log(Level.INFO,
                "Logging that a "+subclass+
                "Exception was thrown in "+method);
    }
}

 

package com.biaoflying;

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

public class SpringAOPDemo {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        ApplicationContext context=
            new FileSystemXmlApplicationContext(
                    "beans-config.xml");
        IHello helloProxy=
            (IHello)context.getBean("helloProxy");
        try{
            helloProxy.hello("biaoflying");
        }catch(Throwable throwable){
            System.err.println(throwable);
        }
    }
}

 

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING/DTD BEAN/EN"
 "http://www.springframework.org/dtd/spring-beans.dtd">
 
<beans>
    <bean id="someThrowAdvice"
        class="com.biaoflying.SomeThrowAdvice"/>
    
    <bean id="helloSpeaker" class="com.biaoflying.HelloSpeaker"/>
    <bean id="helloProxy"
        class="org.springframework.aop.framework.ProxyFactoryBean">
        <property name="proxyInterfaces">
            <value>com.biaoflying.IHello</value>
        </property>
        <property name="target">
            <ref bean="helloSpeaker"/>
        </property>
        <property name="interceptorNames">
            <list>
                <value>someThrowAdvice</value>
            </list>
        </property>
    </bean>
</beans>

  四，更为细化的AOP programming。

  通过定义Ponitcut来实现更为细化的AOP编程，如可以指定在Target的某个方法执行时加入advice。

package com.biaoflying;

public interface IHello {
    public void helloNewbie(String name);
    public void helloMaster(String name);
}

 

package com.biaoflying;

public class HelloSpeaker implements IHello {
    public void helloNewbie(String name){
        System.out.println("Hello "+name+" newbie");
    }
    public void helloMaster(String name){
        System.out.println("Hello "+name+" will be master");
    }
}

 

package com.biaoflying;

import java.lang.reflect.Method;
import java.util.logging.*;
import org.springframework.aop.MethodBeforeAdvice;

public class LogBeforeAdvice
        implements MethodBeforeAdvice{
    private Logger logger=
        Logger.getLogger(this.getClass().getName());
    
    public void before(Method method,Object[] args,
            Object target)throws Throwable{
        logger.log(Level.INFO,"Method starts..."+method);
    }
}

 

package com.biaoflying;

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

public class SpringAOPDemo {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        ApplicationContext context=
            new FileSystemXmlApplicationContext(
                    "beans-config1.xml");
        IHello helloProxy=
            (IHello)context.getBean("helloProxy");
        helloProxy.helloNewbie("abio");
        helloProxy.helloMaster("biaoflying");
    }
}

 

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING/DTD BEAN/EN"
 "http://www.springframework.org/dtd/spring-beans.dtd">
 
<beans>
    <bean id="logBeforeAdvice"
        class="com.biaoflying.LogBeforeAdvice"/>
    <bean id="helloAdvisor"
      class="org.springframework.aop.
       support.NameMatchMethodPointcutAdvisor">
        <property name="mappedName">
            <value>hello*</value>
        </property>
        <property name="advice">
            <ref bean="logBeforeAdvice"/>
        </property>
    </bean>
    
    <bean id="helloSpeaker"   class="com.
       biaoflying.HelloSpeaker"/>
    <bean id="helloProxy"
        class="org.springframework.
        aop.framework.ProxyFactoryBean">
        <property name="proxyInterfaces">
            <value>com.biaoflying.IHello</value>
        </property>
        <property name="target">
            <ref bean="helloSpeaker"/>
        </property>
        <property name="interceptorNames">
            <list>
                <value>helloAdvisor</value>
            </list>
        </property>
    </bean>
</beans>

  另外一个静态PointcutAdvisor为RegexpMethodPointcutAdvisor,更改以上的配置：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING/DTD BEAN/EN"
 "http://www.springframework.org/dtd/spring-beans.dtd">
 
<beans>
    <bean id="logBeforeAdvice"
        class="com.biaoflying.LogBeforeAdvice"/>
    <bean id="helloAdvisor"
        class="org.springframework.aop.
          support.RegexpMethodPointcutAdvisor">
        <property name="pattern">
          <value>.*hello.*</value>
        </property>
        <property name="advice">
            <ref bean="logBeforeAdvice"/>
        </property>
    </bean>
    
    <bean id="helloSpeaker"  class="com.biaoflying.
       HelloSpeaker"/>
    <bean id="helloProxy"
        class="org.springframework.
           aop.framework.ProxyFactoryBean">
        <property name="proxyInterfaces">
            <value>com.biaoflying.IHello</value>
        </property>
        <property name="target">
            <ref bean="helloSpeaker"/>
        </property>
        <property name="interceptorNames">
            <list>
                <value>helloAdvisor</value>
            </list>
        </property>
    </bean>
</beans>

  两者都可以得到一下的输出：

信息: Method starts...public abstract void com.biaoflying.IHello.helloNewbie(java.lang.String)
2008-3-22 18:38:22 com.biaoflying.LogBeforeAdvice before
信息: Method starts...public abstract void com.biaoflying.IHello.helloMaster(java.lang.String)
Hello abio newbie
Hello biaoflying will be master