Spring AOP系列之四：前置通知

  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()。
}