Spring+Maven学习实验- Spring AOP面向切面编程（一）
本文内容纲要：
- 4 种类型的通知（ 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 种类型的通知（ 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 。
1.pom.xml
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.shiyanlou.spring</groupId>
<artifactId>aop</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<name>aop</name>
<url>http://maven.apache.org</url>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>4.2.0.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>4.2.0.RELEASE</version>
</dependency>
</dependencies>
</project>
2.CustomerService.java
package com.shiyanlou.spring.aop;public class CustomerService {
private String name;
private String url;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getUrl() {
return url;
}
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 url:"+this.url);
}
public void printThrowException() {
throw new IllegalArgumentException();
}
}
3.SrpingAOP.xml
<?xml version="1.0" encoding="UTF-8"?><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.xsd">
<bean id="customerService" class="com.shiyanlou.spring.aop.CustomerService">
<property name="name" value="zoey"/>
<property name="url" value="http://shiyanlou.com"/>
</bean>
</beans>
4.App.java
package com.shiyanlou.spring.aop;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[]{"SpringAOP.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) {
}
}
}
4 种类型的通知（ Advice ）
1.Before Advice
method 运行前，将运行下面的代码
HijackBeforeMethod.java 如下:
package com.shiyanlou.spring.aop;import java.lang.reflect.Method;
import org.springframework.aop.MethodBeforeAdvice;
public class HijackBeforeMethod implements MethodBeforeAdvice{
public void before(Method arg0, Object[] arg1, Object arg2)
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 定义想用哪个 class ( advice )劫持 target 。 ApringAOP.xml 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"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="customerService" class="com.shiyanlou.spring.aop.CustomerService">
<property name="name" value="zoey"/>
<property name="url" value="http://shiyanlou.com"/>
</bean>
<bean id="hijackBeforeMethodBean" class="com.shiyanlou.spring.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>
用 Spring proxy 之前，必须添加 CGLIB2 类库，，以下是 pom.xml 依赖：
<dependency> <groupId>org.glassfish.hk2.external</groupId>
<artifactId>cglib</artifactId>
<version>2.2.0-b23</version>
</dependency>
app.java
package com.shiyanlou.spring.aop;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[]{"SpringAOP.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) {
}
}
}
运行结果：
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.shiyanlou.spring.aop;import java.lang.reflect.Method;
import org.springframework.aop.AfterReturningAdvice;
public class HijackAfterMethod implements AfterReturningAdvice {
public void afterReturning(Object arg0, Method arg1, Object[] arg2,
Object arg3) throws Throwable {
System.out.println("After method hijack");
}
}
SpringAOP.xml
<?xml version="1.0" encoding="UTF-8"?><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.xsd">
<bean id="customerService" class="com.shiyanlou.spring.aop.CustomerService">
<property name="name" value="zoey"/>
<property name="url" value="http://shiyanlou.com"/>
</bean>
<bean id="hijackBeforeMethodBean" class="com.shiyanlou.spring.aop.HijackBeforeMethod"/>
<bean id="hijackAfterMethodBean" class="com.shiyanlou.spring.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>
App.java
package com.shiyanlou.spring.aop;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[]{"SpringAOP.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) {
}
}
}
运行结果：
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.shiyanlou.spring.aop;import org.springframework.aop.ThrowsAdvice;
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 ，ApringAdvice.xml 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"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="customerService" class="com.shiyanlou.spring.aop.CustomerService">
<property name="name" value="zoey"/>
<property name="url" value="http://shiyanlou.com"/>
</bean>
<bean id="hijackBeforeMethodBean" class="com.shiyanlou.spring.aop.HijackBeforeMethod"/>
<bean id="hijackAfterMethodBean" class="com.shiyanlou.spring.aop.HijackAfterMethod"/>
<bean id="hijackThrowExceptionBean" class="com.shiyanlou.spring.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>
运行结果：
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.shiyanlou.spring.aop;import java.lang.reflect.Method;
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 ，ApringAOP.xml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"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="customerService" class="com.shiyanlou.spring.aop.CustomerService">
<property name="name" value="zoey"/>
<property name="url" value="http://shiyanlou.com"/>
</bean>
<bean id="hijackBeforeMethodBean" class="com.shiyanlou.spring.aop.HijackBeforeMethod"/>
<bean id="hijackAfterMethodBean" class="com.shiyanlou.spring.aop.HijackAfterMethod"/>
<bean id="hijackThrowExceptionBean" class="com.shiyanlou.spring.aop.HijackThrowException"/>
<bean id="hijackAroundMethodBean" class="com.shiyanlou.spring.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>
运行app.java结果：
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
本文内容总结：4 种类型的通知（ Advice ），2 After Returning Advice，3 Afetr Throwing Advice，4 Around Advice，
原文链接：https://www.cnblogs.com/zoeyqq/p/6553612.html
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