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, Yiibaicut , 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。
- Yiibaicut – 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。
再次回顾上一个 Spring AOP通知的例子。
File : CustomerService.java
package com.yiibai.customer.services;
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();
}
}
File : applicationContext.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.yiibai.customer.services.CustomerService">
<property name="name" value="Yong Mook Kim" />
<property name="url" value="http://www.yiibai.com" />
</bean>
<bean id="hijackAroundMethodBeanAdvice" class="com.yiibai.aop.HijackAroundMethod" />
<bean id="customerServiceProxy"
class="org.springframework.aop.framework.ProxyFactoryBean">
<property name="target" ref="customerService" />
<property name="interceptorNames">
<list>
<value>hijackAroundMethodBeanAdvice</value>
</list>
</property>
</bean>
</beans>
File : HijackAroundMethod.java
package com.yiibai.aop;
import java.util.Arrays;
import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
public class HijackAroundMethod implements MethodInterceptor {
@Override
public Object invoke(MethodInvocation methodInvocation) throws Throwable {
System.out.println("Method name : "
+ methodInvocation.getMethod().getName());
System.out.println("Method arguments : "
+ Arrays.toString(methodInvocation.getArguments()));
System.out.println("HijackAroundMethod : Before method hijacked!");
try {
Object result = methodInvocation.proceed();
System.out.println("HijackAroundMethod : Before after hijacked!");
return result;
} catch (IllegalArgumentException e) {
System.out.println("HijackAroundMethod : Throw exception hijacked!");
throw e;
}
}
}
执行它
package com.yiibai.common;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import com.yiibai.customer.services.CustomerService;
public class App {
public static void main(String[] args) {
ApplicationContext appContext = new ClassPathXmlApplicationContext(
new String[] { "applicationContext.xml" });
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) {
}
}
}
输出
************************* Method name : printName Method arguments : [] HijackAroundMethod : Before method hijacked! Customer name : Yiibai HijackAroundMethod : Before after hijacked! ************************* Method name : printURL Method arguments : [] HijackAroundMethod : Before method hijacked! Customer website : http://www.yiibai.com HijackAroundMethod : Before after hijacked! ************************* Method name : printThrowException Method arguments : [] HijackAroundMethod : Before method hijacked! HijackAroundMethod : Throw exception hijacked!
客户服务类的全部方法被截获。后来，我们展示如何使用“切入点”只拦截printName()方法。
切入点的例子
可以通过以下两种方式相匹配的方法：
- 名称匹配
- 正则表达式匹配
1.切入点 - 名称匹配的例子
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="customerYiibaicut"
class="org.springframework.aop.support.NameMatchMethodYiibaicut">
<property name="mappedName" value="printName" />
</bean>
创建 DefaultYiibaicutAdvisor 通知 bean，通知和切入点相关联。
<bean id="customerAdvisor" class="org.springframework.aop.support.DefaultYiibaicutAdvisor"> <property name="pointcut" ref="customerYiibaicut" /> <property name="advice" ref="hijackAroundMethodBeanAdvice" /> </bean>
更换代理“interceptorNames”到“customerAdvisor”（它是“hijackAroundMethodBeanAdvice”）。
<bean id="customerServiceProxy" class="org.springframework.aop.framework.ProxyFactoryBean"> <property name="target" ref="customerService" /> <property name="interceptorNames"> <list> <value>customerAdvisor</value> </list> </property> </bean>
全部bean配置文件
<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.yiibai.customer.services.CustomerService">
<property name="name" value="Yiibai" />
<property name="url" value="http://www.yiibai.com" />
</bean>
<bean id="hijackAroundMethodBeanAdvice" class="com.yiibai.aop.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="customerYiibaicut"
class="org.springframework.aop.support.NameMatchMethodYiibaicut">
<property name="mappedName" value="printName" />
</bean>
<bean id="customerAdvisor"
class="org.springframework.aop.support.DefaultYiibaicutAdvisor">
<property name="pointcut" ref="customerYiibaicut" />
<property name="advice" ref="hijackAroundMethodBeanAdvice" />
</bean>
</beans>
再次运行，输出
************************* Method name : printName Method arguments : [] HijackAroundMethod : Before method hijacked! Customer name : Yiibai HijackAroundMethod : Before after hijacked! ************************* Customer website : http://www.yiibai.com *************************
现在，只拦截 printName()方法。
YiibaicutAdvisor
Spring提供了YiibaicutAdvisor类来保存工作声明advisor和切入点到不同的bean，可以使用 NameMatchMethodYiibaicutAdvisor 两者结合成一个 bean。
<bean id="customerAdvisor" class="org.springframework.aop.support.NameMatchMethodYiibaicutAdvisor"> <property name="mappedName" value="printName" /> <property name="advice" ref="hijackAroundMethodBeanAdvice" /> </bean>
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 – RegexpMethodYiibaicutAdvisor.
<bean id="customerAdvisor" class="org.springframework.aop.support.RegexpMethodYiibaicutAdvisor"> <property name="patterns"> <list> <value>.*URL.*</value> </list> </property> <property name="advice" ref="hijackAroundMethodBeanAdvice" /> </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。
