入門 43 - Before, After Returning Advice - OpenSource Project

　　在Spring中實現Before Advice或是After Returning Advice，作法與Interceptor類別，只要分別實現org.springframework.aop.MethodBeforeAdvice及org.springframework.aop.AfterReturningAdvice，兩個介面的定義如下：

　代碼:

MethodBeforeAdvice.java

public interface MethodBeforeAdvice extends BeforeAdvice { 
    void before(Method m, Object[] args, Object target) throws Throwable; 
}

　代碼:

AfterReturningAdvice.java

public interface AfterReturningAdvice extends Advice { 
    void afterReturning(Object returnValue, Method m, Object[] args, Object target) 
            throws Throwable; 
}

　　MethodBeforeAdvice的before()方法會在被呼叫的方法之前調用，它不需要如Interceptor呼叫MethodInvocation的proceed()方法，在進入方法前BeforeAdvice被調用的順序由Bean定義檔中設定的順序決定。

　　AfterReturningAdvice的afterReturning()方法會在被呼叫的方法之後調用，它可以存取傳回值，但不能改變其值，無論是Interceptor、Before Advice或是After Returning Advice，當發生例外時，會沿著interceptor鏈往上傳播。

　　來看實際的設定例子，我們分別實現MethodBeforeAdvice及AfterReturningAdvice：

　代碼:

LogBeforeAdvice.java

package onlyfun.caterpillar; 

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

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); 
   } 
}

　代碼:

LogAfterAdvice.java

package onlyfun.caterpillar; 

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

public class LogAfterAdvice implements AfterReturningAdvice { 
    private Logger logger = Logger.getLogger(this.getClass().getName()); 
    
    public void afterReturning(Object object, Method method, 
                               Object[] args, Object target) 
                                  throws Throwable { 
        logger.log(Level.INFO, "method ends..." + method); 
   } 
}

　　其它像是IHello介面、HelloSepaker類別與測試程式，都與之前主題中介紹的相同，不需作任何的修改，我們只要改變Bean設定檔的內容，就可以改變這些Advice的介入，Bean設定檔的內容如下：

　代碼:

<?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="onlyfun.caterpillar.LogBeforeAdvice"/> 
    <bean id="logAfterAdvice" class="onlyfun.caterpillar.LogAfterAdvice"/> 

    <bean id="logBeforeAdvisor" class="org.springframework.aop.support.RegexpMethodPointcutAdvisor"> 
        <property name="advice"> 
            <ref bean="logBeforeAdvice"/> 
        </property> 
        <property name="patterns"> 
            <value>onlyfun\.caterpillar\.IHello\.hello</value> 
        </property> 
    </bean> 

    <bean id="logAfterAdvisor" class="org.springframework.aop.support.RegexpMethodPointcutAdvisor"> 
        <property name="advice"> 
            <ref bean="logAfterAdvice"/> 
        </property> 
        <property name="patterns"> 
            <value>onlyfun\.caterpillar\.IHello\.morning</value> 
        </property> 
    </bean> 

    <bean id="helloSpeaker" class="onlyfun.caterpillar.HelloSpeaker"/> 
    
    <bean id="helloProxy" class="org.springframework.aop.framework.ProxyFactoryBean"> 
        <property name="proxyInterfaces"> 
            <value>onlyfun.caterpillar.IHello</value> 
        </property> 
        <property name="target"> 
            <ref bean="helloSpeaker"/> 
        </property> 
        <property name="interceptorNames"> 
            <list> 
                <value>logBeforeAdvisor</value> 
                <value>logAfterAdvisor</value> 
            </list> 
        </property> 
    </bean> 
</beans>

　　這邊仍使用了RegexpMethodPointcutAdvisor，分別設定在執行hello()之前介入logBeforeAdvisor，以及morning()方法之後使用logAfterAdvisor。