Spring 中基于 AOP 的 @AspectJ
@AspectJ 作为通过 Java 5 注释注释的普通的 Java 类，它指的是声明 aspects 的一种风格。
通过在你的基于架构的 XML 配置文件中包含以下元素，@AspectJ 支持是可用的。
<aop:aspectj-autoproxy/>
声明一个 aspect
Aspects 类和其他任何正常的 bean 一样，除了它们将会用 @AspectJ 注释之外，它和其他类一样可能有方法和字段，如下所示：
package org.xyz;
import org.aspectj.lang.annotation.Aspect;
@Aspect
public class AspectModule {
}
它们将在 XML 中按照如下进行配置，就和其他任何 bean 一样：
<bean id="myAspect" class="org.xyz.AspectModule">
<!-- configure properties of aspect here as normal -->
</bean>
声明一个切入点
一个切入点有助于确定使用不同建议执行的感兴趣的连接点（即方法）。在处理基于配置的 XML 架构时，切入点的声明有两个部分：
-
一个切入点表达式决定了我们感兴趣的哪个方法会真正被执行。
-
一个切入点标签包含一个名称和任意数量的参数。方法的真正内容是不相干的，并且实际上它应该是空的。
下面的示例中定义了一个名为 ‘businessService’ 的切入点，该切入点将与 com.xyz.myapp.service 包下的类中可用的每一个方法相匹配：
import org.aspectj.lang.annotation.Pointcut;
@Pointcut("execution(* com.xyz.myapp.service.*.*(..))") // expression
private void businessService() {} // signature
下面的示例中定义了一个名为 ‘getname’ 的切入点，该切入点将与 com.tutorialspoint 包下的 Student 类中的 getName() 方法相匹配：
import org.aspectj.lang.annotation.Pointcut;
@Pointcut("execution(* com.tutorialspoint.Student.getName(..))")
private void getname() {}
声明建议
你可以使用 @{ADVICE-NAME} 注释声明五个建议中的任意一个，如下所示。这假设你已经定义了一个切入点标签方法 businessService()：
@Before("businessService()")
public void doBeforeTask(){
...
}
@After("businessService()")
public void doAfterTask(){
...
}
@AfterReturning(pointcut = "businessService()", returning="retVal")
public void doAfterReturnningTask(Object retVal){
// you can intercept retVal here.
...
}
@AfterThrowing(pointcut = "businessService()", throwing="ex")
public void doAfterThrowingTask(Exception ex){
// you can intercept thrown exception here.
...
}
@Around("businessService()")
public void doAroundTask(){
...
}
基于 AOP 的 @AspectJ 示例
-
新建Spring项目
-
在项目中添加 Spring AOP 指定的库文件 aspectjrt.jar， aspectjweaver.jar 和 aspectj.jar。
-
保证aspectjweaver.jar的版本在1.8以上，否则会报错。
-
创建 Java 类 Logging， Student 和 MainApp
这里是 Logging.java 文件的内容。这实际上是 aspect 模块的一个示例，它定义了在各个点调用的方法。
package hello;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Pointcut;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.After;
import org.aspectj.lang.annotation.AfterThrowing;
import org.aspectj.lang.annotation.AfterReturning;
import org.aspectj.lang.annotation.Around;
//import org.springframework.aop.aspectj.AspectJAfterThrowingAdvice;
@Aspect
public class Logging {
/** Following is the definition for a pointcut to select
* all the methods available. So advice will be called
* for all the methods.
*/
@Pointcut("execution(* hello.*.*(..))")
private void selectAll(){}
/**
* This is the method which I would like to execute
* before a selected method execution.
*/
@Before("selectAll()")
public void beforeAdvice(){
System.out.println("Going to setup student profile.");
}
/**
* This is the method which I would like to execute
* after a selected method execution.
*/
@After("selectAll()")
public void afterAdvice(){
System.out.println("Student profile has been setup");
}
/**
* This is the method which I would like to execute
* when any method returns.
*/
@AfterReturning(pointcut = "selectAll()", returning = "retVal")
public void afterReturningAdvice(Object retVal){
System.out.println("Returning:"+retVal.toString());
}
/**
* This is the method which I would like to execute
* if there is an exception raised.
*/
@AfterThrowing(pointcut = "selectAll()", throwing = "ex")
public void AfterThrowingAdvice(IllegalArgumentException ex){
System.out.println("there has been an exception:"+ex.toString());
}
}
下面是 Student.java 文件的内容：
package hello;
//import org.springframework.beans.factory.annotation.Autowired;
public class Student {
private int age;
private String name;
public void setAge(int age){
this.age = age;
}
public int getAge(){
System.out.println("age:"+age);
return age;
}
public void setName(String name){
this.name = name;
}
public String getName(){
System.out.println("name:"+name);
return name;
}
public void printThrowException(){
System.out.println("Exception raised");
throw new IllegalArgumentException();
}
}
下面是 MainApp.java 文件的内容：
package hello;
//import org.springframework.context.support.AbstractApplicationContext;
//import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
//import org.springframework.context.annotation.*;
public class MainApp {
public static void main(String[] args) {
ApplicationContext context =
new ClassPathXmlApplicationContext("Beans.xml");
Student student = (Student) context.getBean("student");
student.getName();
student.getAge();
//student.printThrowException();
}
}
下面是配置文件 Beans.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"
xmlns:aop="http://www.springframework.org/schema/aop"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/aop
http://www.springframework.org/schema/aop/spring-aop.xsd">
<!--aop:config>
<aop:aspect id="log" ref="logging">
<aop:pointcut id="selectAll" expression="execution(* hello.*.*(..))"/>
<aop:before pointcut-ref="selectAll" method="beforeAdvice"/>
<aop:after pointcut-ref="selectAll" method="afterAdvice"/>
<aop:after-returning pointcut-ref="selectAll"
returning="retVal"
method="afterReturningAdvice"/>
<aop:after-throwing pointcut-ref="selectAll"
throwing="ex"
method="AfterThrowingAdvice"/>
</aop:aspect>
</aop:config-->
<aop:aspectj-autoproxy/>
<!-- Definition for student bean -->
<bean id="student" class="hello.Student">
<property name="name" value="番茄"/>
<property name="age" value="10"/>
</bean>
<!-- Definition for logging aspect -->
<bean id="logging" class="hello.Logging">
</bean>
</beans>
运行一下应用程序
Going to setup student profile.
name:番茄
Student profile has been setup
Returning:番茄
Going to setup student profile.
age:10
Student profile has been setup
Returning:10
Process finished with exit code 0
每天学习一点点，每天进步一点点。