Spring3系列：Spring AOP——Advice

野性酷女 2022-07-13 12:22 156阅读 0赞

为尊重别人的劳动成果，本文转自：[Spring3系列9- Spring AOP——Advice][Spring3_9- Spring AOP_Advice]

Spring AOP即Aspect-oriented programming，面向切面编程，是作为面向对象编程的一种补充，专门用于处理系统中分布于各个模块（不同方法）中的交叉关注点的问题。简单地说，就是一个拦截器（interceptor）拦截一些处理过程。例如，当一个method被执行，Spring AOP能够劫持正在运行的method，在method执行前或者后加入一些额外的功能。

在Spring AOP中，支持4中类型的通知（Advice）

Before advice      ——method执行前通知

After returning advice ——method返回一个结果后通知

After throwing advice – method抛出异常后通知

Around advice – 环绕通知，结合了以上三种

下边这个例子解释Spring AOP怎样工作。

首先一个简单的不使用AOP的例子。

先创建一个简单的Service，为了稍后演示，这个类中加了几个简单的打印method。

CustomerService.java如下：

![复制代码][copycode.gif]

package com.lei.demo.aop.advice;
    
    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();
        }
    
    }

![复制代码][copycode.gif]

Xml配置文件Apring-AOP-Advice.xml如下：

![复制代码][copycode.gif]

运行以下代码App.java：

![复制代码][copycode.gif]

package com.lei.demo.aop.advice;
    
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    
    public class App {
    
        public static void main(String[] args) {
            ApplicationContext appContext = new ClassPathXmlApplicationContext(
                    new String[] { "Spring-AOP-Advice.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) {
     
            }
     
        }
    
    }

![复制代码][copycode.gif]

运行结果：

\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*

Customer name : LeiOOLei

\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*

Customer website : http://www.cnblogs.com/leiOOlei/

\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*

## 1.      Before Advice ##

创建一个实现了接口MethodBeforeAdvice的class，method运行前，将运行下边的代码

HijackBeforeMethod.java如下:

![复制代码][copycode.gif]

package com.lei.demo.aop.advice;
    
    import java.lang.reflect.Method;
    import org.springframework.aop.MethodBeforeAdvice;
    
    public class HijackBeforeMethod implements MethodBeforeAdvice {
    
        public void before(Method arg0, Object[] args, Object target)
                throws Throwable {
            System.out.println("HijackBeforeMethod : Before method hijacked!");
            
        }
    
    }

![复制代码][copycode.gif]

在配置文件中加入新的bean配置HijackBeforeMethod，然后创建一个新的代理（proxy），命名为customerServiceProxy。

“target”定义你想劫持哪个bean；

“interceptorNames”定义你想用哪个class(advice)劫持target。

Apring-AOP-Advice.xml如下：

![复制代码][copycode.gif]

<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.lei.demo.aop.advice.CustomerService">
            <property name="name" value="LeiOOLei" />
            <property name="url" value="http://www.cnblogs.com/leiOOlei/" />
        </bean>
        
        <bean id="hijackBeforeMethodBean" class="com.lei.demo.aop.advice.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>

![复制代码][copycode.gif]

注意：

用Spring proxy之前，必须添加CGLIB2类库，，以下是pom.xml依赖

<dependency>
            <groupId>cglib</groupId>
            <artifactId>cglib</artifactId>
            <version>2.2.2</version>
        </dependency>

运行如下代码，注意代理

App.java如下

![复制代码][copycode.gif]

package com.lei.demo.aop.advice;
    
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    
    public class App {
    
        public static void main(String[] args) {
            ApplicationContext appContext = new ClassPathXmlApplicationContext(
                    new String[] { "Spring-AOP-Advice.xml" });
     
            CustomerService cust = (CustomerService) appContext.getBean("customerServiceProxy");
     
            System.out.println("使用Spring AOP 如下");
            System.out.println("*************************");
            cust.printName();
            System.out.println("*************************");
            cust.printURL();
            System.out.println("*************************");
            
            try {
                cust.printThrowException();
            } catch (Exception e) {
     
            }
     
        }
    
    }

![复制代码][copycode.gif]

输出结果：

使用Spring AOP 如下

\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*

HijackBeforeMethod : Before method hijacked!

Customer name : LeiOOLei

\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*

HijackBeforeMethod : Before method hijacked!

Customer website : http://www.cnblogs.com/leiOOlei/

\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*

HijackBeforeMethod : Before method hijacked!

每一个customerService的method运行前，都将先执行HijackBeforeMethod的before方法。

## 2.      After Returning Advice ##

创建一个实现了接口AfterReturningAdvice的class，method运行后，直到返回结果后，才运行下边的代码，如果没有返回结果，将不运行切入的代码。

HijackAfterMethod.java如下：

![复制代码][copycode.gif]

package com.lei.demo.aop.advice;
    
    import java.lang.reflect.Method;
    import org.springframework.aop.AfterReturningAdvice;
    
    public class HijackAfterMethod implements AfterReturningAdvice {
    
        public void afterReturning(Object returnValue, Method method, Object[] args,
                Object target) throws Throwable {
            System.out.println("HijackAfterMethod : After method hijacked!");
    
        }
    
    }

![复制代码][copycode.gif]

修改bean配置文件，加入*hijackAfterMethodBean*配置，Apring-AOP-Advice.xml如下：

![复制代码][copycode.gif]

<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.lei.demo.aop.advice.CustomerService">
            <property name="name" value="LeiOOLei" />
            <property name="url" value="http://www.cnblogs.com/leiOOlei/" />
        </bean>
        
        <bean id="hijackBeforeMethodBean" class="com.lei.demo.aop.advice.HijackBeforeMethod" />
        <bean id="hijackAfterMethodBean" class="com.lei.demo.aop.advice.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>

![复制代码][copycode.gif]

现在再运行App.java后输出如下：

使用Spring AOP 如下

\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*

Customer name : LeiOOLei

HijackAfterMethod : After method hijacked!

\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*

Customer website : http://www.cnblogs.com/leiOOlei/

HijackAfterMethod : After method hijacked!

\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*

可以看到输出结果，每一个customerService的method运行返回结果后，都将再执行HijackAfterMethod的afterReturning方法。但是执行到cust.printThrowException()后，直接抛出异常，方法没有正常执行完毕（或者说没有返回结果），所以不运行切入的afterReturning方法。

## 3.      Afetr Throwing Advice ##

创建一个实现了ThrowsAdvice接口的class，劫持IllegalArgumentException异常，目标method运行时，抛出IllegalArgumentException异常后，运行切入的方法。

HijackThrowException.java如下：

![复制代码][copycode.gif]

package com.lei.demo.aop.advice;
    
    import org.springframework.aop.ThrowsAdvice;
    
    import sun.awt.SunToolkit.IllegalThreadException;
    
    public class HijackThrowException implements ThrowsAdvice {
    
        public void afterThrowing(IllegalArgumentException e) throws Throwable {
            System.out.println("HijackThrowException : Throw exception hijacked!");
        }
    
    }

![复制代码][copycode.gif]

修改bean配置文件，加入了hijackThrowExceptionBean，Apring-AOP-Advice.xml如下：

![复制代码][copycode.gif]

<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.lei.demo.aop.advice.CustomerService">
            <property name="name" value="LeiOOLei" />
            <property name="url" value="http://www.cnblogs.com/leiOOlei/" />
        </bean>
        
        <bean id="hijackBeforeMethodBean" class="com.lei.demo.aop.advice.HijackBeforeMethod" />
        <bean id="hijackAfterMethodBean" class="com.lei.demo.aop.advice.HijackAfterMethod" />
        <bean id="hijackThrowExceptionBean" class="com.lei.demo.aop.advice.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>

![复制代码][copycode.gif]

运行结果如下:

使用Spring AOP 如下

\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*

Customer name : LeiOOLei

\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*

Customer website : http://www.cnblogs.com/leiOOlei/

\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*

HijackThrowException : Throw exception hijacked!

当运行CustomerService中的printThrowException方法时，认为的抛出IllegalArgumentException异常，被HijackThrowException截获，运行其中的afterThrowing方法。注意，如果抛出异常不是IllegalArgumentException，则不能被截获。

## 4.      Around Advice ##

结合了以上3种形式的Advice，创建一个实现了接口MethodInterceptor的class，你必须通过methodInvocation.proceed()来调用原来的方法，即通过调用methodInvocation.proceed()来调用CustomerService中的每一个方法，当然也可以不调用原方法。

HijackAroundMethod.java如下：

![复制代码][copycode.gif]

package com.lei.demo.aop.advice;
    
    import java.util.Arrays;
    import org.aopalliance.intercept.MethodInterceptor;
    import org.aopalliance.intercept.MethodInvocation;
    
    public class HijackAroundMethod implements MethodInterceptor {
    
        public Object invoke(MethodInvocation methodInvocation) throws Throwable {
            System.out.println("Method name : "
                    + methodInvocation.getMethod().getName());
            System.out.println("Method arguments : "
                    + Arrays.toString(methodInvocation.getArguments()));
     
            // 相当于  MethodBeforeAdvice
            System.out.println("HijackAroundMethod : Before method hijacked!");
     
            try {
                // 调用原方法，即调用CustomerService中的方法
                Object result = methodInvocation.proceed();
     
                // 相当于 AfterReturningAdvice
                System.out.println("HijackAroundMethod : After method hijacked!");
     
                return result;
     
            } catch (IllegalArgumentException e) {
                // 相当于 ThrowsAdvice
                System.out.println("HijackAroundMethod : Throw exception hijacked!");
                throw e;
            }
        }
    
    }

![复制代码][copycode.gif]

修改bean配置文件，加入了*hijackAroundMethodBean*，Apring-AOP-Advice.xml如下：

![复制代码][copycode.gif]

<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.lei.demo.aop.advice.CustomerService">
            <property name="name" value="LeiOOLei" />
            <property name="url" value="http://www.cnblogs.com/leiOOlei/" />
        </bean>
        
        <bean id="hijackBeforeMethodBean" class="com.lei.demo.aop.advice.HijackBeforeMethod" />
        <bean id="hijackAfterMethodBean" class="com.lei.demo.aop.advice.HijackAfterMethod" />
        <bean id="hijackThrowExceptionBean" class="com.lei.demo.aop.advice.HijackThrowException" />
        <bean id="hijackAroundMethodBean" class="com.lei.demo.aop.advice.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>

![复制代码][copycode.gif]

执行App.java，输出结果：

使用Spring AOP 如下

\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*

Method name : printName

Method arguments : \[\]

HijackAroundMethod : Before method hijacked!

Customer name : LeiOOLei

HijackAroundMethod : After method hijacked!

\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*

Method name : printURL

Method arguments : \[\]