Spring3系列9-Spring AOP——Advice
本文内容纲要：
- 1. Before Advice- 2. After Returning Advice
- 3. Afetr Throwing Advice
- 4. Around 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：
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();
}
}
Xml配置文件Apring-AOP-Advice.xml如下：
<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>
</beans>
运行以下代码App.java：
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) {
}
}
}
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:
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!");
}
}
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：
<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>
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
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) {
}
}
}
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：
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!");
}
}
修改bean配置文件，加入hijackAfterMethodBean配置，Apring-AOP-Advice.xml如下：
<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>
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：
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!");
}
}
修改bean配置文件，加入了hijackThrowExceptionBean，Apring-AOP-Advice.xml如下：
<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>
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：
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;
}
}
}
修改bean配置文件，加入了hijackAroundMethodBean，Apring-AOP-Advice.xml如下：
<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>
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 : []
HijackAroundMethod : Before method hijacked!
Customer website : http://www.cnblogs.com/leiOOlei/
HijackAroundMethod : After method hijacked!
*************************
Method name : printThrowException
Method arguments : []
HijackAroundMethod : Before method hijacked!
HijackAroundMethod : Throw exception hijacked!
CustomerService中每一个方法的调用，都会执行HijackAroundMethod中的invoke方法，可以看到整个切入点将目标around。
大多数的Spring开发者只用Around Advice，因为它能够实现所有类型的Advice。在实际的项目开发中，我们还是要尽量选择适合的Advice。
在以上的例子中，CustomerService中的所有方法都被自动拦截，但是大多数情况下，我们不需要拦截一个class中的所有方法，而是拦截符合条件的方法。这时，我们就需要用到Pointcut and Advice，即切入点和通知，以后的章节中会逐渐介绍。
本文内容总结：1. Before Advice，2. After Returning Advice，3. Afetr Throwing Advice，4. Around Advice，
原文链接：https://www.cnblogs.com/jcomet/p/5570452.html
以上是 Spring3系列9-Spring AOP——Advice 的全部内容， 来源链接： utcz.com/z/362893.html
