浅谈spring——增强接口（六）

来源：互联网发布：与制工作室长板淘宝编辑：程序博客网时间：2024/06/07 09:31

AOP支持5种类型的增强。

增强接口关系图：

1）前置增强：BeforeAdvice，表示在目标方法执行前实施增强。

2）后置增强：AfterReturningAdvice，表示在目标方法执行后实施增强。

3）环绕增强：MethodInterceptor，表示在目标方法执行前后实施增强

4）异常增强：ThrowsAdvice，表示在目标方法抛出异常后实施增强

5）引介增强：IntroductionInterceptor，表示在目标类中添加一些新的属性和方法

xml配置：

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<bean id="greetingBefore" class="com.baobaotao.advice.GreetingBeforeAdvice" />
<bean id="target" class="com.baobaotao.advice.NaiveWaiter" />
<bean id="waiter" class="org.springframework.aop.framework.ProxyFactoryBean"
p:proxyInterfaces="com.baobaotao.advice.Waiter" ##代理接口
p:target-ref="target" ##指定对哪个bean增强
p:interceptorNames="greetingBefore"/> ##指定的增强

代码实例

1）前置增强：

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import java.lang.reflect.Method;
import org.springframework.aop.MethodBeforeAdvice;
public class GreetingBeforeAdvice implements MethodBeforeAdvice {
public void before(Method method, Object[] args, Object obj) throws Throwable {
String clientName = (String)args[0];
System.out.println("How are you！Mr."+clientName+".");
}
}

method:目标类的方法

args:目标类方法的入参

obj:目标类实例

2）后置增强：

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import java.lang.reflect.Method;
import org.springframework.aop.AfterReturningAdvice;
public class GreetingAfterAdvice implements AfterReturningAdvice {
public void afterReturning(Object returnObj, Method method, Object[] args,
Object obj) throws Throwable {
System.out.println("Please enjoy yourself!");
}
}

returnObj：目标实例方法返回的结果

method：目标类方法

args：目标实例方法的入参

obj:目标类实例

3）环绕增强

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import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
public class GreetingInterceptor implements MethodInterceptor {
public Object invoke(MethodInvocation invocation) throws Throwable {
Object[] args = invocation.getArguments();//获取入参
String clientName = (String)args[0];
System.out.println("How are you！Mr."+clientName+".");
Object obj = invocation.proceed();//反射机制调用目标方法
System.out.println("Please enjoy yourself!");
return obj;
}
}

MethodInvocation不但封装了目标方法及其入参数组，还封装了目标方法所在的实例对象

4）抛出异常的增强

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import java.lang.reflect.Method;
import org.springframework.aop.ThrowsAdvice;
public class TransactionManager implements ThrowsAdvice {
public void afterThrowing(Method method, Object[] args, Object target,
Exception ex) throws Throwable {
System.out.println("-----------");
System.out.println("method:" + method.getName());
System.out.println("抛出异常:" + ex.getMessage());
System.out.println("成功回滚事务。");
}
}

ThrowAdvice异常抛出增强接口没有定义任何方法，它是一个标识接口，在运行时由spring使用反射机制自行判断。

method：目标类方法

args：目标实例方法的入参

target:目标类实例

ex：要捕获的异常

其中前三个参数可以缺省。afterThrowing方法，可以定义多个，当目标方法抛出异常时，spring会自动找出最匹配的增强方法。

5）引介增强：比较特殊，不是在目标方法周围织入增强，而是为目标类增加新的方法和属性，属于类级别而非方法级别。

接口

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public interface Monitorable {
void setMonitorActive(boolean active);
}

增强代码

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import org.aopalliance.intercept.MethodInvocation;
import org.springframework.aop.support.DelegatingIntroductionInterceptor;
public class ControllablePerformaceMonitor extends
DelegatingIntroductionInterceptor implements Monitorable{
private ThreadLocal<Boolean> MonitorStatusMap = new ThreadLocal<Boolean>();
public void setMonitorActive(boolean active) {
MonitorStatusMap.set(active);
}
public Object invoke(MethodInvocation mi) throws Throwable {
Object obj = null;
if (MonitorStatusMap.get() != null && MonitorStatusMap.get()) {
PerformanceMonitor.begin(mi.getClass().getName() + "."
+ mi.getMethod().getName());
obj = super.invoke(mi);
PerformanceMonitor.end();
} else {
obj = super.invoke(mi);
}
return obj;
}
}

xml配置

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<bean id="pmonitor" class="com.baobaotao.introduce.ControllablePerformaceMonitor" />
<bean id="forumServiceTarget" class="com.baobaotao.introduce.ForumService" />
<bean id="forumService" class="org.springframework.aop.framework.ProxyFactoryBean"
p:interfaces="com.baobaotao.introduce.Monitorable"
p:target-ref="forumServiceTarget"
p:interceptorNames="pmonitor"
p:proxyTargetClass="true" />
lt;/beans>

调用代码

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import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class TestIntroduce {
public static void main(String[] args) {
String configPath = "com/baobaotao/introduce/beans.xml";
ApplicationContext ctx = new ClassPathXmlApplicationContext(configPath);
ForumService forumService = (ForumService)ctx.getBean("forumService");
forumService.removeForum(10);
forumService.removeTopic(1022);
Monitorable moniterable = (Monitorable)forumService; //监控开启
moniterable.setMonitorActive(true);
forumService.removeForum(10);
forumService.removeTopic(1022);
}
}

引介增强与之前的四类增强有较大区别，首先需要指定引介增强所实现的接口Monitorable；其次只能通过为目标类创建子类的方式生成代理，必须将p:proxyTargetClass设置成"true"

可以直观理解为下图：

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