Spring AOP系列之四：前置通知

编程技术  /  houtizong 发布于 3年前   140

  通过实现org.springframework.aop.MethodBeforeAdvice来完成前置通知：

public class CarBeforeAdvice implements MethodBeforeAdvice {@Override        // method 目标类方法，args 方法参数，target 目标对象public void before(Method method, Object[] args, Object target) throws Throwable {System.out.println("Welcome to the car shop");}}

Spring配置文件beans-before-advice.xml

<?xml version="1.0" encoding="UTF-8"?><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.xsd"  default-autowire="byName">  <bean id="car" class="com.john.spring.aop.Car">  <property name="name" value="Superb" /><property name="price" value="220000" />  </bean>    <bean id="carBeforeAdvice" class="com.john.spring.aop.CarBeforeAdvice" />    <bean id="proxyBean" class="org.springframework.aop.framework.ProxyFactoryBean">  <property name="proxyInterfaces">  <value>com.john.spring.aop.Vehicle</value></property><property name="interceptorNames"><list><value>carBeforeAdvice</value></list></property><property name="target"><ref bean="car" /></property>  </bean></beans>

测试：

public static void main(String[] args) {ApplicationContext ctx = new ClassPathXmlApplicationContext(new String[] { "beans-before-advice.xml" });Vehicle vehicle = (Vehicle) ctx.getBean("proxyBean");vehicle.info();}

输出：
Welcome to the car shop
Car name: Superb, price: 220000


附：
info()调用的时候，调用org.springframework.aop.framework.adapter.MethodBeforeAdviceAdapter类的getInterceptor方法：

class MethodBeforeAdviceAdapter implements AdvisorAdapter, Serializable {public boolean supportsAdvice(Advice advice) { // 是否支持指定通知return (advice instanceof MethodBeforeAdvice);}public MethodInterceptor getInterceptor(Advisor advisor) {MethodBeforeAdvice advice = (MethodBeforeAdvice) advisor.getAdvice(); // 获取通知return new MethodBeforeAdviceInterceptor(advice);}}

然后调用org.springframework.aop.framework.adapter.MethodBeforeAdviceInterceptor的invoke方法：

public Object invoke(MethodInvocation mi) throws Throwable {this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis() ); // 前置通知实现类的before方法。这里是CarBeforeAdvice类的实例return mi.proceed(); // 目标类方法的执行。这里是info()。}