SpringAOP原理

public interface UserService {// 被拦截的接口
public void printUser(String user);
}

public class UserServiceImp implements UserService {// 实现UserService接口
public void printUser(String user) ...{
System.out.println("printUser user:" + user);// 显示user
}
}

import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
public class UserInterceptor implements MethodInterceptor{// AOP方法拦截器
public Object invoke(MethodInvocation arg0) throws Throwable {
try {
if (arg0.getMethod().getName().equals("printUser")){
// 拦截方法是否是UserService接口的printUser方法
Object[] args = arg0.getArguments();// 被拦截的参数
System.out.println("user:" + args[0]);
arg0.getArguments()[0] = "hello!";// 修改被拦截的参数
}
System.out.println(arg0.getMethod().getName() + "---!");
return arg0.proceed();// 运行UserService接口的printUser方法
}catch (Exception e) ...{
throw e;
}
}
}

import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.context.support.FileSystemXmlApplicationContext;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.Resource;
import org.springframework.web.context.support.WebApplicationContextUtils;public class TestInterceptor{
public static void main(String[] args){
ApplicationContext ctx = new FileSystemXmlApplicationContext(
"classpath:applicationContext.xml");
// ApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext.xml");
UserService us = (UserService) ctx.getBean("userService");
us.printUser("shawn");
}
}

<?xml version="1.0" encoding="UTF-8"?><!--
- Application context definition for JPetStore's business layer.
- Contains bean references to the transaction manager and to the DAOs in
- dataAccessContext-local/jta.xml (see web.xml's "contextConfigLocation"). Jpetstore 的应用上下文定义，包含事务管理和引用了在 dataAccessContext-local/jta.xml(具体使用了哪个要看 web.xml 中的 'contextConfigLocation' 的配置）中注册的DAO
-->
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:aop="http://www.springframework.org/schema/aop"
xmlns:tx="http://www.springframework.org/schema/tx"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.0.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.0.xsd"> <!-- ========================= GENERAL DEFINITIONS ========================= --> <!-- Configurer that replaces ${...} placeholders with values from properties files
占位符的值将从列出的属性文件中抽取出来
-->
<!-- (in this case, mail and JDBC related properties) -->
<bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
<property name="locations">
<list>
<value>WEB-INF/mail.properties</value>
<value>WEB-INF/jdbc.properties</value>
</list>
</property>
</bean> <!-- MailSender used by EmailAdvice
指定用于发送邮件的 javamail 实现者，这里使用了 spring 自带的实现。此 bean 将被 emailAdvice 使用
-->
<bean id="mailSender" class="org.springframework.mail.javamail.JavaMailSenderImpl">
<property name="host" value="${mail.host}"/>
</bean> <!-- ========================= BUSINESS OBJECT DEFINITIONS ======================== --> <!-- 不需要，因为被 SpringMVC 的实现使用 Generic validator for Account objects, to be used for example by the Spring web tier -->
<bean id="accountValidator" class="org.springframework.samples.jpetstore.domain.logic.AccountValidator"/> <!-- 不需要，因为被 SpringMVC 的实现使用 Generic validator for Order objects, to be used for example by the Spring web tier -->
<bean id="orderValidator" class="org.springframework.samples.jpetstore.domain.logic.OrderValidator"/> <!--
主要的商业逻辑对象，即我们所说的门面对象
注入了所有的DAO，这些DAO是引用了 dataAccessContext-xxx.xml 中定义的DAO
门面对象中的所有方法的事务控制将通过下面的 aop:config 来加以控制 - JPetStore primary business object (default implementation).
- Transaction advice gets applied through the AOP configuration below.
-->
<bean id="petStore" class="org.springframework.samples.jpetstore.domain.logic.PetStoreImpl">
<property name="accountDao" ref="accountDao"/>
<property name="categoryDao" ref="categoryDao"/>
<property name="productDao" ref="productDao"/>
<property name="itemDao" ref="itemDao"/>
<property name="orderDao" ref="orderDao"/>
</bean> <!-- ========================= ASPECT CONFIGURATION ======================== -->
<!-- AOP配置，用来控制哪些方法将需要进行事务处理，采用了AspectJ 的语法 -->
<aop:config>
<!--
This definition creates auto-proxy infrastructure based on the given pointcut,
expressed in AspectJ pointcut language. Here: applying the advice named
"txAdvice" to all methods on classes named PetStoreImpl.
-->
<!-- 指出在 PetStoreFacade 的所有方法都将采用 txAdvice(在紧接着的元素中定义了）事务方针，注意，我们这里虽然指定的是接口 PetStoreFacace, 但其暗示着其所有的实现类也将
同样具有这种性质，因为本身就是实现类的方法在执行的，接口是没有方法体的。 -->
<aop:advisor pointcut="execution(* *..PetStoreFacade.*(..))" advice-ref="txAdvice"/> <!--
This definition creates auto-proxy infrastructure based on the given pointcut,
expressed in AspectJ pointcut language. Here: applying the advice named
"emailAdvice" to insertOrder(Order) method of PetStoreImpl
-->
<!-- 当执行 PetStoreFacade.insertOrder方法，该方法最后一个参数为Order类型时（其实我们的例子中只有一个 insertOrder 方法，但这告诉了我们，当我们的接口或类中有重载了的方法，
并且各个重载的方法可能使用不同的拦截机机制时，我们可以通过方法的参数加以指定），将执行emailAdvice(在最后定义的那个元素）-->
<aop:advisor pointcut="execution(* *..PetStoreFacade.insertOrder(*..Order))" advice-ref="emailAdvice"/> </aop:config> <!--

事务方针声明，用于控制采用什么样的事务策略
Transaction advice definition, based on method name patterns.
Defaults to PROPAGATION_REQUIRED for all methods whose name starts with
"insert" or "update", and to PROPAGATION_REQUIRED with read-only hint
for all other methods.
-->
<tx:advice id="txAdvice">
<tx:attributes>
<tx:method name="insert*"/>
<tx:method name="update*"/>
<tx:method name="*" read-only="true"/>
</tx:attributes>
</tx:advice> <!-- 拦截机，用于在适当的时机(通过AOP配置，如上面)在方法执行成功后发送邮件
AOP advice used to send confirmation email after order has been submitted -->
<!-- -->
<bean id="emailAdvice" class="org.springframework.samples.jpetstore.domain.logic.SendOrderConfirmationEmailAdvice">
<property name="mailSender" ref="mailSender"/>
</bean> <!-- ========================= 忽略 REMOTE EXPORTER DEFINITIONS ======================== --></beans>