Spring中的Advice部类及其应用 _Web前端

Spring中的Advice类型及其应用

在Spring中，Advice都是通过Interceptor来实现的，主要有以下几种：

1. 环绕Advice：

//例子摘自Spring reference

public interface MethodInterceptor extends Interceptor {
      Object invoke(MethodInvocation invocation) throws Throwable;
}
public class DebugInterceptor implements MethodInterceptor {

    public Object invoke(MethodInvocation invocation) throws Throwable {
        System.out.println("Before: invocation=[" + invocation + "]"); //(1)
        Object rval = invocation.proceed();
        System.out.println("Invocation returned"); //(2)
        return rval;
    }
}

环绕advice类似一个拦截器链，这个拦截器链的中心就是被拦截的方法。在程序(1)(2)我们可以加入我们自己的代码，以表示在方法执行前后我们需要干什么。invocation.proceed()方法运行指向连接点的拦截器链并返回proceed()的结果。

2. Before Advice

public interface MethodBeforeAdvice extends BeforeAdvice {
void before(Method m, Object[] args, Object target) throws Throwable;
}

一个更简单的通知类型是before 通知。它不需要 MethodInvocation对象，因为它只是在进入方法之前被调用。before advice的一个主要优点是它不需要调用proceed()方法，因此就不会发生无意间运行拦截器链失败的情况。

3. After advice

public interface AfterReturningAdvice extends Advice {
void afterReturning(Object returnValue, Method m, Object[] args, Object target) throws Throwable;
}

一个After advice可以访问返回值（但不能进行修改），被调用方法，方法参数以及目标对象。

4.Throws Advice

//ThrowsAdvice 是一个空接口，起标识作用
public interface ThrowsAdvice extends Advice {

}
//所给对象必须实现一个或者多个针对特定类型的异常通知方法，格式如下
afterThrowing([Method], [args], [target], subclassOfThrowable)
//只有最后一个参数是必须的。因此异常通知方法对方法及参数的需求，方法的签名将从一到四个参数之间变化。

最后还有一个是introduction advice，这个我想什么时候自己单独做个例子理解一下。

做了个例子如下，想像一个用户登录场景：在登录之前，我们对其输入的用户名进行有效性检查；登录成功后，我们记上用户登录次数；如果登录失败，则进行异常处理。实现代码如下：

package com.learn.spring.test.advisor;
//登录的业务代码
public interface LoginService {
    void login(String name, String password) throws UnauthorityException;
}

public class LoginServiceImpl implements LoginService {

    public void login(String name, String password) throws UnauthorityException {
            check(name, password);
            System.err.println(name + " is logining system...");
    }

    private void check(String name, String password) throws UnauthorityException {
            if("myyate".equals(name) && "pass".equals(password) ) {
                     System.err.println(name + " passed check....");
            } else {
                    throw new UnauthorityException("invalid password");
            }
    }
}

//用户名检查拦截器

public class LoginNameCheckInterceptor implements MethodBeforeAdvice {

    public void before(Method method, Object[] args, Object target) throws Throwable {
         System.err.println("check user's name is valid?");
         if(args[0] == null || "".equals(args[0].toString().trim())) {
               throw new IllegalArgumentException();
         }
    }
}

//用户登录次数统计拦截器
public class LoginCountInterceptor implements AfterReturningAdvice ...{

    public void afterReturning(Object returnValue, Method method, Object[] args, Object target) throws Throwable ...{
    System.err.println("Counting the login counts of " + args[0]);
    }
}

//异常处理拦截器

public class ExceptionThrowInterceptor implements ThrowsAdvice {

    public void afterThrowing(Method m, Object[] args, Object target, IllegalArgumentException ex) throws Throwable {
    System.err.println("Login name is wrong, exception: " + ex);
    }

    public void afterThrowing(Method m, Object[] args, Object target, UnauthorityException ex) {
       System.err.println(target.getClass() + "." + m.getName() +
           "() throw a exception: " + ex.getMessage());
    }
}

配置文件如下：

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:aop="http://www.springframework.org/schema/aop"

xmlns:tx="http://www.springframework.org/schema/tx"

xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd

http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.0.xsd

http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.0.xsd">

<bean id="loginServiceTarget"

class="com.learn.spring.test.advisor.LoginServiceImpl"/>

<bean id="loginNameCheckInterceptor"

class="com.learn.spring.test.advisor.LoginNameCheckInterceptor"/>

<!--

<bean id="loginCheckInterceptor"

class="com.learn.spring.test.advisor.LoginCheckInterceptor"/>

-->

<bean id="loginCountInterceptor"

class="com.learn.spring.test.advisor.LoginCountInterceptor"/>

<bean id="exceptionThrowInterceptor"

class="com.learn.spring.test.advisor.ExceptionThrowInterceptor"/>

<list>

<value>com.learn.spring.test.advisor.LoginService</value>

</list>

</property>

<list>

<value>loginNameCheckInterceptor</value>

<value>loginCountInterceptor</value>

<value>exceptionThrowInterceptor</value>

</list>

</property>

</bean>

</beans>

测试代码运行：

public class Test {

    public static void main(String[] args) throws Exception {
        BeanFactory bf =
            BeanFactoryFactory.getBeanFactory("beans.xml", Test.class);
        LoginService ls = (LoginService) bf.getBean("loginService");
        ls.login("myyate", "pass");
    }
}

输出结果：

check user's name is valid?
myyate passed check....
myyate is logining system...
Counting the login counts of myyate