Spring3系列10- Spring AOP——Pointcut，Advisor

上一篇的Spring AOP Advice例子中，Class（CustomerService）中的全部method都被自动的拦截了。但是大多情况下，你只需要一个方法去拦截一两 个method。这样就引入了Pointcut（切入点）的概念，它允许你根据method的名字去拦截指定的method。另外，一个Pointcut 必须结合一个Advisor来使用。

 

在Spring AOP中，有3个常用的概念，Advices、Pointcut、Advisor，解释如下，

Advices：表示一个method执行前或执行后的动作。

Pointcut：表示根据method的名字或者正则表达式去拦截一个method。

Advisor：Advice和Pointcut组成的独立的单元，并且能够传给proxy factory 对象。

 

下边来回顾一下上一篇例子中的代码

CustomerService.java

package com.lei.demo.aop.advice;

public class CustomerService {

    private String name;
    private String url;
 
    public void setName(String name) {
        this.name = name;
    }
 
    public void setUrl(String url) {
        this.url = url;
    }
 
    public void printName() {
        System.out.println("Customer name : " + this.name);
    }
 
    public void printURL() {
        System.out.println("Customer website : " + this.url);
    }
 
    public void printThrowException() {
        throw new IllegalArgumentException();
    }

}

配置文件Spring-AOP-Advice.xml：

<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-2.5.xsd">
 
    <bean id="customerService" class="com.lei.demo.aop.advice.CustomerService">
        <property name="name" value="LeiOOLei" />
        <property name="url" value="http://www.cnblogs.com/leiOOlei/" />
    </bean>
    
    <bean id="hijackAroundMethodBean" class="com.lei.demo.aop.advice.HijackAroundMethod" />
 
    <bean id="customerServiceProxy" class="org.springframework.aop.framework.ProxyFactoryBean">
        <property name="target" ref="customerService" />
        <property name="interceptorNames">
            <list>
                <value>hijackAroundMethodBean</value>
            </list>
        </property>
    </bean>
 
</beans>

HijackAroundMethod.java

package com.lei.demo.aop.advice;

import java.util.Arrays;
import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;

public class HijackAroundMethod implements MethodInterceptor {

    public Object invoke(MethodInvocation methodInvocation) throws Throwable {
        System.out.println("Method name : "
                + methodInvocation.getMethod().getName());
        System.out.println("Method arguments : "
                + Arrays.toString(methodInvocation.getArguments()));
 
        // 相当于  MethodBeforeAdvice
        System.out.println("HijackAroundMethod : Before method hijacked!");
 
        try {
            // 调用原方法，即调用CustomerService中的方法
            Object result = methodInvocation.proceed();
 
            // 相当于 AfterReturningAdvice
            System.out.println("HijackAroundMethod : After method hijacked!");
 
            return result;
 
        } catch (IllegalArgumentException e) {
            // 相当于 ThrowsAdvice
            System.out.println("HijackAroundMethod : Throw exception hijacked!");
            throw e;
        }
    }

}

运行如下App.java

package com.lei.demo.aop.advice;

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

public class App {

    public static void main(String[] args) {
        ApplicationContext appContext = new ClassPathXmlApplicationContext(
                new String[] { "Spring-AOP-Advice.xml" });

        
        System.out.println("使用Spring AOP 如下");
        CustomerService cust = (CustomerService) appContext.getBean("customerServiceProxy");
        System.out.println("*************************");
        cust.printName();
        System.out.println("*************************");
        cust.printURL();
        System.out.println("*************************");
        
        try {
            cust.printThrowException();
        } catch (Exception e) {
 
        }
 
    }

}

运行结果：

使用Spring AOP 如下

*************************

Method name : printName

Method arguments : []

HijackAroundMethod : Before method hijacked!

Customer name : LeiOOLei

HijackAroundMethod : After method hijacked!

*************************

Method name : printURL

Method arguments : []

HijackAroundMethod : Before method hijacked!

Customer website : http://www.cnblogs.com/leiOOlei/

HijackAroundMethod : After method hijacked!

*************************

Method name : printThrowException

Method arguments : []

HijackAroundMethod : Before method hijacked!

HijackAroundMethod : Throw exception hijacked!

 

上边的结果中，CustomerService.java中，全部的method方法全部被拦截了，下边我们将展示怎样利用Pointcuts只拦截printName()。

 

你可以用名字匹配法和正则表达式匹配法去匹配要拦截的method。

1.      Pointcut——Name match example

通过pointcut和advisor拦截printName()方法。

创建一个NameMatchMethodPointcut的bean，将你想拦截的方法的名字printName注入到属性mappedName，如下

<bean id="customerPointcut"
        class="org.springframework.aop.support.NameMatchMethodPointcut">
        <property name="mappedName" value="printName" />
</bean>

创建一个DefaultPointcutAdvisor的advisor bean，将pointcut和advice关联起来。

<bean id="customerAdvisor"
        class="org.springframework.aop.support.DefaultPointcutAdvisor">
        <property name="pointcut" ref="customerPointcut" />
        <property name="advice" ref=" hijackAroundMethodBean " />
</bean>

更改代理的interceptorNames值，将上边的advisor（ customerAdvisor）替代原来的hijackAroundMethodBean。

<bean id="customerServiceProxy"
        class="org.springframework.aop.framework.ProxyFactoryBean">
 
        <property name="target" ref="customerService" />
 
        <property name="interceptorNames">
            <list>
                <value>customerAdvisor</value>
            </list>
        </property>
</bean>

所有的配置文件如下：

<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-2.5.xsd">
 
    <bean id="customerService" class="com.lei.demo.aop.advice.CustomerService">
        <property name="name" value="LeiOOLei" />
        <property name="url" value="http://www.cnblogs.com/leiOOlei/" />
    </bean>
 
    <bean id="hijackAroundMethodBean" class="com.lei.demo.aop.advice.HijackAroundMethod" />
 
    <bean id="customerServiceProxy" class="org.springframework.aop.framework.ProxyFactoryBean">
 
        <property name="target" ref="customerService" />
 
        <property name="interceptorNames">
            <list>
                <value>customerAdvisor</value>
            </list>
        </property>
    </bean>
 
    <bean id="customerPointcut"class="org.springframework.aop.support.NameMatchMethodPointcut">
        <property name="mappedName" value="printName" />
    </bean>
 
    <bean id="customerAdvisor" class="org.springframework.aop.support.DefaultPointcutAdvisor">
        <property name="pointcut" ref="customerPointcut" />
        <property name="advice" ref=" hijackAroundMethodBean " />
    </bean>
 
</beans>

再运行一下App.java，输出结果如下：

使用Spring AOP 如下

*************************

Method name : printName

Method arguments : []

HijackAroundMethod : Before method hijacked!

Customer name : LeiOOLei

HijackAroundMethod : After method hijacked!

*************************

Customer website : http://www.cnblogs.com/leiOOlei/

*************************

 

以上运行结果显示，只拦截了printName()方法。

 

注意：

以上配置中pointcut和advisor可以合并在一起配置，即不用单独配置customerPointcut和customerAdvisor，只要配置customerAdvisor时class选择NameMatchMethodPointcutAdvisor如下：

<bean id="customerAdvisor" class="org.springframework.aop.support.NameMatchMethodPointcutAdvisor">
        <property name="mappedName" value="printName" />
        <property name="advice" ref="hijackAroundMethodBean" />
</bean>

这样，整个配置文件如下：

<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-2.5.xsd">
 
    <bean id="customerService" class="com.lei.demo.aop.advice.CustomerService">
        <property name="name" value="LeiOOLei" />
        <property name="url" value="http://www.cnblogs.com/leiOOlei/" />
    </bean>
    
    <bean id="hijackAroundMethodBean" class="com.lei.demo.aop.advice.HijackAroundMethod" />
 
    <bean id="customerServiceProxy" class="org.springframework.aop.framework.ProxyFactoryBean">
        <property name="target" ref="customerService" />
        <property name="interceptorNames">
            <list>
                <value>customerAdvisor</value>
            </list>
        </property>
    </bean>
    
    
    <bean id="customerAdvisor" class="org.springframework.aop.support.NameMatchMethodPointcutAdvisor">
        <property name="mappedName" value="printName" />
        <property name="advice" ref="hijackAroundMethodBean" />
    </bean>
 
</beans>

　　实际上这种做法将method名字与具体的advice捆绑在一起，有悖于Spring松耦合理念，如果将method名字单独配置成pointcut（切入点），advice和pointcut的结合会更灵活，使一个pointcut可以和多个advice结合。

2.      Pointcut——Regular exxpression match example

你可以配置用正则表达式匹配需要拦截的method，如下配置

<bean id="customerAdvisor" class="org.springframework.aop.support.RegexpMethodPointcutAdvisor">
        <property name="patterns">
            <list>
                <value>.*URL.*</value>
            </list>
        </property>
        <property name="advice" ref="hijackAroundMethodBeanAdvice" />
    </bean>

现在，你可以拦截名字中包含URL字符的method了，在实际工作中，你可以用它来管理DAO层，例如，你可以用“.*DAO.*”来拦截所有DAO层中的相关业务。