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/beanshttp://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 MethodBeforeAdviceSystem.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 AfterReturningAdviceSystem.out.println("HijackAroundMethod : After method hijacked!");return result;} catch (IllegalArgumentException e) {// 相当于 ThrowsAdviceSystem.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/beanshttp://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/beanshttp://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。