Spring学习(十五)----- Spring AOP通知实例 – Advice

基础

Spring AOP(面向方面编程)框架，用于在模块化方面的横切关注点。简单得说，它只是一个拦截器拦截一些过程，例如，当一个方法执行，Spring AOP 可以劫持一个执行的方法，在方法执行之前或之后添加额外的功能。

在Spring AOP中，有 4 种类型通知(advices)的支持：

• 通知(Advice)之前 - 该方法执行前运行.                                               (实现 MethodBeforeAdvice接口)
• 通知(Advice)返回之后 – 运行后，该方法返回一个结果                       (实现AfterReturningAdvice接口)
  
• 通知(Advice)抛出之后 – 运行方法抛出异常后，                                  (实现ThrowsAdvice接口，并创建一个afterThrowing方法拦截)
  
• 环绕通知 – 环绕方法执行运行，结合以上这三个通知。                      (实现MethodInterceptor接口;必须调用“methodInvocation.proceed();)
  

下面的例子显示Spring AOP 通知如何工作。

简单的 Spring 例子

创建一个简单的客户服务类及一个print方法作为演示。

package com.yiibai.customer.services;

public class CustomerService {
    private String name;
    private String url;

    public void setName(String name) {
        this.name = name;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public void printName() {
        System.out.println("Customer name : " + this.name);
    }

    public void printURL() {
        System.out.println("Customer website : " + this.url);
    }

    public void printThrowException() {
        throw new IllegalArgumentException();
    }

}

File : applicationContext.xml – 一个bean配置文件

<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-2.5.xsd">

    <bean id="customerService" class="com.yiibai.customer.services.CustomerService">
        <property name="name" value="YiiBaii Mook Kim" />
        <property name="url" value="http://www.yiibai.com" />
    </bean>

</beans>

执行它

package com.yiibai.common;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.yiibai.customer.services.CustomerService;

public class App {
    public static void main(String[] args) {
        ApplicationContext appContext = new ClassPathXmlApplicationContext(
                new String[] { "Spring-Customer.xml" });

        CustomerService cust = (CustomerService) appContext.getBean("customerService");

        System.out.println("*************************");
        cust.printName();
        System.out.println("*************************");
        cust.printURL();
        System.out.println("*************************");
        try {
            cust.printThrowException();
        } catch (Exception e) {

        }

    }
}

输出

*************************
Customer name : Yiibai Mook Kim
*************************
Customer website : http://www.yiibai.com
*************************

一个简单的Spring项目用来注入(DI)bean和输出一些字符串。

Spring AOP 通知

现在，附加 Spring AOP 建议到上述的客户服务。

1. 之前通知

它会在方法执行之前执行。创建一个实现 MethodBeforeAdvice 接口的类。

package com.yiibai.aop;

import java.lang.reflect.Method;
import org.springframework.aop.MethodBeforeAdvice;

public class HijackBeforeMethod implements MethodBeforeAdvice
{
    @Override
    public void before(Method method, Object[] args, Object target)
        throws Throwable {
            System.out.println("HijackBeforeMethod : Before method hijacked!");
    }
}

在 bean 配置文件(applicationContext.xml)，创建一个 bean 的 HijackBeforeMethod 类，并命名为“customerServiceProxy” 作为一个新的代理对象。

• ‘target’ – 定义你想拦截的bean。
• ‘interceptorNames’ – 定义要应用这个代理/目标对象的类(通知)。

<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-2.5.xsd">

    <bean id="customerService" class="com.yiibai.customer.services.CustomerService">
        <property name="name" value="Yiibai Mook Kim" />
        <property name="url" value="http://www.yiibai.com" />
    </bean>

    <bean id="hijackBeforeMethodBean" class="com.yiibai.aop.HijackBeforeMethod" />

    <bean id="customerServiceProxy" 
                 class="org.springframework.aop.framework.ProxyFactoryBean">

        <property name="target" ref="customerService" />

        <property name="interceptorNames">
            <list>
                <value>hijackBeforeMethodBean</value>
            </list>
        </property>
    </bean>
</beans>

再次运行它，现在得到新的 customerServiceProxy bean，而不是原来的CustomerService bean。

package com.yiibai.common;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import com.yiibai.customer.services.CustomerService;

public class App {
    public static void main(String[] args) {
        ApplicationContext appContext = new ClassPathXmlApplicationContext(
                new String[] { "Spring-Customer.xml" });

        CustomerService cust = 
                                (CustomerService) appContext.getBean("customerServiceProxy");

        System.out.println("*************************");
        cust.printName();
        System.out.println("*************************");
        cust.printURL();
        System.out.println("*************************");
        try {
            cust.printThrowException();
        } catch (Exception e) {

        }

    }
}

输出结果

*************************
HijackBeforeMethod : Before method hijacked!
Customer name : Yiibai Mook Kim
*************************
HijackBeforeMethod : Before method hijacked!
Customer website : http://www.yiibai.com
*************************
HijackBeforeMethod : Before method hijacked!

它将运行 HijackBeforeMethod 的 before() 方法，在每个 CustomerService 的方法之前执行。

2.返回后通知

该方法返回一个结果之后它将执行。创建一个实现AfterReturningAdvice接口的类。

package com.yiibai.aop;

import java.lang.reflect.Method;
import org.springframework.aop.AfterReturningAdvice;

public class HijackAfterMethod implements AfterReturningAdvice
{
    @Override
    public void afterReturning(Object returnValue, Method method,
        Object[] args, Object target) throws Throwable {
            System.out.println("HijackAfterMethod : After method hijacked!");
    }
}

bean配置文件

<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-2.5.xsd">

    <bean id="customerService" class="com.yiibai.customer.services.CustomerService">
        <property name="name" value="Yong Mook Kim" />
        <property name="url" value="http://www.yiibai.com" />
    </bean>

    <bean id="hijackAfterMethodBean" class="com.yiibai.aop.HijackAfterMethod" />

    <bean id="customerServiceProxy"  class="org.springframework.aop.framework.ProxyFactoryBean">

        <property name="target" ref="customerService" />

        <property name="interceptorNames">
            <list>
                <value>hijackAfterMethodBean</value>
            </list>
        </property>
    </bean>
</beans>

再次运行，输出

*************************
Customer name : Yiibai Mook Kim
HijackAfterMethod : After method hijacked!
*************************
Customer website : http://www.yiibai.com
HijackAfterMethod : After method hijacked!
*************************

它将运行 HijackAfterMethod 的 afterReturning()方法，在每次 CustomerService 方法返回结果之后。

3.抛出后通知

它将在执行方法抛出一个异常后。创建一个实现ThrowsAdvice接口的类，并创建一个afterThrowing方法拦截抛出：IllegalArgumentException异常。

package com.yiibai.aop;

import org.springframework.aop.ThrowsAdvice;

public class HijackThrowException implements ThrowsAdvice {
    public void afterThrowing(IllegalArgumentException e) throws Throwable {//afterThrowing:不能修改;IllegalArgumentException:捕获什么异常就发什么异常类型(Throwable:捕获任何异常);
        System.out.println("HijackThrowException : Throw exception hijacked!");
    }
}

bean配置文件

<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-2.5.xsd">

    <bean id="customerService" class="com.yiibai.customer.services.CustomerService">
        <property name="name" value="Yong Mook Kim" />
        <property name="url" value="http://www.yiibai.com" />
    </bean>

    <bean id="hijackThrowExceptionBean" class="com.yiibai.aop.HijackThrowException" />

    <bean id="customerServiceProxy" 
                 class="org.springframework.aop.framework.ProxyFactoryBean">

        <property name="target" ref="customerService" />

        <property name="interceptorNames">
            <list>
                <value>hijackThrowExceptionBean</value>
            </list>
        </property>
    </bean>
</beans>

再次运行，输出

*************************
Customer name : Yiibai Mook Kim
*************************
Customer website : http://www.yiibai.com
*************************
HijackThrowException : Throw exception hijacked!

它将运行 HijackThrowException 的 afterThrowing()方法，如果 CustomerService 的方法抛出异常。

4.环绕通知

它结合了上面的三个通知，在方法执行过程中执行。创建一个实现了MethodInterceptor接口的类。必须调用“methodInvocation.proceed();” 继续在原来的方法执行，否则原来的方法将不会执行。

package com.yiibai.aop;

import java.util.Arrays;

import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;

public class HijackAroundMethod implements MethodInterceptor { //MethodInterceptor :方法拦截器
    @Override
    public Object invoke(MethodInvocation methodInvocation) throws Throwable {

        System.out.println("Method name : "
                + methodInvocation.getMethod().getName());
        System.out.println("Method arguments : "
                + Arrays.toString(methodInvocation.getArguments()));

        // same with MethodBeforeAdvice
        System.out.println("HijackAroundMethod : Before method hijacked!");

        try {
            // proceed to original method call
            Object result = methodInvocation.proceed();

            // same with AfterReturningAdvice
            System.out.println("HijackAroundMethod : Before after hijacked!");

            return result;

        } catch (IllegalArgumentException e) {
            // same with ThrowsAdvice
            System.out.println("HijackAroundMethod : Throw exception hijacked!");
            throw e;
        }
    }
}

bean配置文件

<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-2.5.xsd">

    <bean id="customerService" class="com.yiibai.customer.services.CustomerService">
        <property name="name" value="Yong Mook Kim" />
        <property name="url" value="http://www.yiibai.com" />
    </bean>

    <bean id="hijackAroundMethodBean" class="com.yiibai.aop.HijackAroundMethod" />

    <bean id="customerServiceProxy" 
                class="org.springframework.aop.framework.ProxyFactoryBean">

        <property name="target" ref="customerService" />

        <property name="interceptorNames">
            <list>
                <value>hijackAroundMethodBean</value>
            </list>
        </property>
    </bean>
</beans>

再次运行，输出

*************************
Method name : printName
Method arguments : []
HijackAroundMethod : Before method hijacked!
Customer name : YiiBai Mook Kim
HijackAroundMethod : Before after hijacked!
*************************
Method name : printURL
Method arguments : []
HijackAroundMethod : Before method hijacked!
Customer website : http://www.yiibai.com 
HijackAroundMethod : Before after hijacked!
*************************
Method name : printThrowException
Method arguments : []
HijackAroundMethod : Before method hijacked!
HijackAroundMethod : Throw exception hijacked!

它将运行HijackAroundMethod 的 invoke()方法，在每一个 CustomerService 方法执行后。