Spring AOP之切点拦截

在上一个Spring AOP通知的例子，一个类的整个方法被自动拦截。但在大多数情况下，可能只需要一种方式来拦截一个或两个方法，这就是为什么引入'切入点'的原因。它允许你通过它的方法名来拦截方法。另外，一个“切入点”必须具有“Advisor' 相关联。

在Spring AOP中，有三个非常专业术语- Advices, Point, Advisor，把它在非官方的方式...

• Advice – 指示之前或方法执行后采取的行动。
• Pointcut– 指明哪些方法应该拦截，通过方法的名称或正则表达式模式。
• Advisor – 分组"通知"和”切入点“成为一个单元，并把它传递到代理工厂对象。

File : CustomerService.java

package com.spring.aop;public class CustomerService {private String name;private String url;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 void printName(){System.out.println("CustomerName :"+this.name);}public void printURL(){System.out.println("CustomerURL "+this.url);}public void  printThrowException() throws IllegalAccessException{throw new IllegalAccessException();}}

File : bean.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.spring.aop.CustomerService">    <property name="name" value="Yahoo"></property>    <property name="url" value="www.yahoo.com"></property>    </bean>    <bean id="hijackAroundMethod" class="com.spring.aop.HijackAroundMethod"></bean>    <bean id="customerserviceProxy"  class="org.springframework.aop.framework.ProxyFactoryBean">    <property name="target" ref="customerservice"></property>    <property name="interceptorNames">    <list>    <value>custmerAdvisor</value>    </list>    </property>    </bean>    <bean id="customerPointcut" class="org.springframework.aop.support.NameMatchMethodPointcut">    <property name="mappedName" value="printName"></property>    </bean>    <bean id="custmerAdvisor" class="org.springframework.aop.support.DefaultPointcutAdvisor">        <property name="pointcut" ref="customerPointcut"></property>    <property name="advice" ref="hijackAroundMethod"></property>    </bean></beans>

然我们看看bean.xml的一些配置信息是什么意思：

通过“切入点”和“advisor”拦截printName()方法。创建NameMatchMethodYiibaicut切入点bean，并提出要在“mappedName”属性值来拦截方法名。

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

创建 DefaultPointcutAdvisor 通知 bean，通知和切入点相关联。

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

更换代理“interceptorNames”到“customerAdvisor”（它是“hijackAroundMethod”）。

<bean id="customerserviceProxy"  class="org.springframework.aop.framework.ProxyFactoryBean">    <property name="target" ref="customerservice"></property>    <property name="interceptorNames">    <list>    <value>custmerAdvisor</value>    </list>    </property>    </bean>

现在，只拦截 printName()方法。

PointcutAdvisor

Spring提供了PintcutAdvisor类来保存工作声明advisor和切入点到不同的bean，可以使用 NameMatchMethodPointcutAdvisor 两者结合成一个 bean。

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

File : HijackAroundMethod.java

package com.spring.aop;import java.util.Arrays;import org.aopalliance.intercept.MethodInterceptor;import org.aopalliance.intercept.MethodInvocation;public class HijackAroundMethod   implements MethodInterceptor{@Overridepublic Object invoke(MethodInvocation methodInvocation) throws Throwable {System.out.println("Method Name "+methodInvocation.getMethod().getName());System.out.println("Argument Name"+methodInvocation.getArguments());System.out.println("HijackAroundMethod Mentod :Before HijackAround");try {Object result = methodInvocation.proceed();System.out.println("HijackAroundMethod Mentod :after HijackAround");return result;} catch (IllegalArgumentException e) {System.out.println("HijackAroundMethod : Throw exception hijacked!");throw e;}}}

执行它

package com.spring.aop;import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;public class Main {public static void main(String[] args) {ApplicationContext context = new ClassPathXmlApplicationContext("bean.xml");CustomerService customerservice = (CustomerService) context.getBean("customerserviceProxy");System.out.println("------------------------------------------");customerservice.printName();System.out.println("------------------------------------------");customerservice.printURL();System.out.println("------------------------------------------");try {customerservice.printThrowException();} catch (IllegalAccessException e) {e.printStackTrace();}}}

再次运行，输出

Method Name printNameArgument Name[Ljava.lang.Object;@543e710eHijackAroundMethod Mentod :Before HijackAroundCustomerName :YahooHijackAroundMethod Mentod :after HijackAround------------------------------------------CustomerURL www.yahoo.com------------------------------------------

2.切入点 - 正则表达式的例子

也可以通过使用正则表达式匹配切入点方法的名称  – RegexpMethodPointcutAdvisor.

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

现在，它拦截方法名称中有“URL”的方法。在实践中，可以用它来管理DAO层，声明“.*DAO.*” 拦截所有的DAO类来支持事务。