循序渐进之Spring AOP(4)

前面描述的几种增强(Advice)都是在目标方法范围内织入，而引介(Introduction)不同，直接在类级别上添加目标未实现的接口方法。

在spring中可以通过扩展DelegatingIntroductionInterceptor类来实现引介增强类。

下面通过这种方式给一辆普通汽车加上无人驾驶功能

接口Auto

public interface Auto {
    void driving();
}

实现类

public class MyCar implements Auto {
    @Override
    public void driving() {
        System.out.println("开车了");
    }
}

新建一个接口Intelligent，它具有一个自动驾驶的方法，我们将把这个方法"添加"到MyCar上

public interface Intelligent {
    void selfDriving();
}

实现类IntelligentCar，注意，继承了DelegatingIntroductionInterceptor类

public class IntelligentCar extends DelegatingIntroductionInterceptor implements Intelligent {

    @Override
    public void selfDriving() {
        System.out.println("开启无人驾驶了, 别挡路");
    }

    public Object invoke(MethodInvocation invocation) throws Throwable {
        Object obj = super.invoke(invocation);
        return obj;
    }
}

applicationContext.xml

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"
    xmlns:aop="http://www.springframework.org/schema/aop"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
  http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
  http://www.springframework.org/schema/aop
  http://www.springframework.org/schema/aop/spring-aop-3.0.xsd">

    <bean id="carTarget" class="demo.aop.MyCar" />
    <bean id="introduceAdvisor" class="org.springframework.aop.support.DefaultIntroductionAdvisor">
        <constructor-arg>
            <bean class="demo.aop.IntelligentCar" />
        </constructor-arg>
    </bean>
    <bean id="myCar" class="org.springframework.aop.framework.ProxyFactoryBean"
        p:target-ref="carTarget"
        p:interceptorNames="introduceAdvisor"
        p:proxyTargetClass="true" />
</beans>

测试代码

public static void main(String[] args) {
    ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");

    Auto car = (Auto)context.getBean("myCar");
    car.driving();
    Intelligent intelligentCar = (Intelligent)car;
    intelligentCar.selfDriving();
}

运行结果

开车了
开启无人驾驶了, 别挡路