循序渐进之Spring AOP(3)

上一篇介绍了几种Advice(增强)，并通过代码演示了生成代理的方式，下面来看通过配置文件配置方式把Advice织入目标类。

注意，配置文件方式仍然不是spring AOP的最好方式，学习配置方式也是为了循序渐进的掌握内核技术。

接口SmartCar

public interface SmartCar {
    void lock(String userName);
}

实现类MyCar

public class MyCar implements SmartCar {
    @Override
    public void lock(String userName) {
        System.out.println(userName + "锁车");
    }
}

定义了两个增强，一个在锁车方法前执行，提示检查窗户是否关闭，一个在锁车方法后执行，"哔哔"声提示锁车成功

public class BeforeAdviceDemo implements MethodBeforeAdvice {
    @Override
    public void before(Method method, Object[] args, Object obj)
            throws Throwable {
        System.out.println("请检查窗户是否关好");
    }
}

public class AfterAdviceDemo implements AfterReturningAdvice {
    @Override
    public void afterReturning(Object returnObj, Method method, Object[] args,
            Object obj) throws Throwable {
        System.out.println("哔哔");
    }
}

applicationContext.xml: 用配置文件来声明代理

<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:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
  http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
  http://www.springframework.org/schema/context
  http://www.springframework.org/schema/context/spring-context-3.0.xsd">

    <bean id="beforeAdvice" class="demo.aop.BeforeAdviceDemo" />
    <bean id="afterAdvice" class="demo.aop.AfterAdviceDemo" />
    <bean id="target" class="demo.aop.MyCar" />

    <bean id="myCar" class="org.springframework.aop.framework.ProxyFactoryBean"
        p:target-ref="target"
        p:proxyTargetClass="true">
        <property name="interceptorNames">
            <list>
                <idref local="beforeAdvice" />
                <idref local="afterAdvice" />
            </list>
        </property>
    </bean>
</beans>

测试代码

public static void main(String[] args) {
    ApplicationContext context = new ClassPathXmlApplicationContext("demo/aop/applicationContext.xml");
    SmartCar myCar = (SmartCar)context.getBean("myCar");
    myCar.lock("Tom");
}

执行结果

请检查窗户是否关好
Tom锁车
哔哔

配置文件中首先声明了3个bean，分别是增强的目标类和两个增强，没有特别的配置内容。重点是ProxyFactoryBean的配置，来看看它可配置的属性和用法。

target	目标对象，ref另一个bean
proxyTargetClass	是否对类进行代理(而不是对接口)，true或false，设置为true时，使用CGLib代理技术
interceptorNames	织入目标对象的Advice(实现了Advisor或者MethodInterceptor接口的bean)
proxyInterfaces	代理所要实现的接口，如果指定了proxyTargetClass=true，此属性会被忽略
optimize	设置为true时，强制使用CGLib代理技术

下面再分别增加一个环绕增强和一个异常抛出增强。

先修改MyCar类，使它能够抛出异常，粗心的约翰会忘记锁车而抛出一个异常

public class MyCar implements SmartCar {
    @Override
    public void lock(String userName) {
        if(userName.equals("Careless John")) {
            throw new RuntimeException(userName + "忘记锁车");
        } else {
            System.out.println(userName + "锁车");
        }
    }
}

环绕增强类

public class AroundAdviceDemo implements MethodInterceptor {
    @Override
    public Object invoke(MethodInvocation invocation) throws Throwable {
        Object[] args = invocation.getArguments();
        String name = (String)args[0];
        System.out.print("Hey, " + name);
        Object obj = invocation.proceed(); //调用目标方法
        System.out.println("Goodbye! " + name);
        return obj;
    }
}

异常抛出增强

public class ThrowsAdviceDemo implements ThrowsAdvice {
    public void afterThrowing(Method method, Object[] args, Object target, Exception ex) throws Throwable {
        System.out.println("捕获异常:" + ex.getMessage());
        System.out.println("(报警)滴滴滴滴滴滴滴滴滴滴滴滴");
    }
}

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:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
  http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
  http://www.springframework.org/schema/context
  http://www.springframework.org/schema/context/spring-context-3.0.xsd">

    <bean id="beforeAdvice" class="demo.aop.BeforeAdviceDemo" />
    <bean id="afterAdvice" class="demo.aop.AfterAdviceDemo" />
    <bean id="aroundAdvice" class="demo.aop.AroundAdviceDemo" />
    <bean id="throwsAdvice" class="demo.aop.ThrowsAdviceDemo" />
    <bean id="target" class="demo.aop.MyCar" />

    <bean id="myCar" class="org.springframework.aop.framework.ProxyFactoryBean"
        p:target-ref="target"
        p:proxyTargetClass="true">
        <property name="interceptorNames">
            <list>
                <idref local="aroundAdvice" />
                <idref local="throwsAdvice" />
                <idref local="beforeAdvice" />
                <idref local="afterAdvice" />
            </list>
        </property>
    </bean>
</beans>

测试代码

public static void main(String[] args) {
    ApplicationContext context = new ClassPathXmlApplicationContext("demo/aop/applicationContext.xml");
    SmartCar myCar = (SmartCar)context.getBean("myCar");
    myCar.lock("Tom");
    System.out.println("-------------------------");
    myCar.lock("Careless John");
}

运行结果

Hey, Tom请检查窗户是否关好
Tom锁车
哔哔
Goodbye! Tom
-------------------------
Hey, Careless John请检查窗户是否关好
捕获异常:Careless John忘记锁车
(报警)滴滴滴滴滴滴滴滴滴滴滴滴

除了上面的四种增强，还有一种特殊的引介增强(Introduction)，在下一篇中单独介绍