Spring AOP - 代理

到目前为止，我们已经使用<aop:config>或< aop:aspectj-autoproxy>声明了切面。我们也可以以编程方式创建代理，并使用代理对象以编程方式调用切面。

语法

//Create object to be proxied
Student student = new Student();

//Create the Proxy Factory
AspectJProxyFactory proxyFactory = new AspectJProxyFactory(student);

//Add Aspect class to the factory
proxyFactory.addAspect(Logging.class);

//Get the proxy object
Student proxyStudent = proxyFactory.getProxy();

//Invoke the proxied method.
proxyStudent.getAge();

其中，

• AspectJProxyFactory - 创建代理对象的工厂类。

• Logging.class - 包含通知的切面类。

• Student - 要被通知的业务类。

为了理解上面提到的与代理相关的概念，让我们编写一个实现代理的示例。为了编写包含一些通知的示例，让我们准备一个可用的 Eclipse IDE，并使用以下步骤创建一个 Spring 应用程序：

以下是Logging.java文件的内容。这实际上是切面模块的一个示例，它定义了在各个点要调用的方法。

package com.tutorialspoint;

import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.PointCut;
import org.aspectj.lang.annotation.Before;

@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(* com.tutorialspoint.Student.getAge(..))")
   private void selectGetAge(){}

   /** 
      * This is the method which I would like to execute
      * before a selected method execution.
   */
   @Before("selectGetAge()")
   public void beforeAdvice(){
      System.out.println("Going to setup student profile.");
   }  
}

以下是Student.java文件的内容。

package com.tutorialspoint;

public class Student {
   private Integer age;
   public void setAge(Integer age) {
      this.age = age;
   }
   public Integer getAge() {
      System.out.println("Age : " + age );
      return age;
   }   
}

以下是MainApp.java文件的内容。

package com.tutorialspoint;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.aop.aspectj.annotation.AspectJProxyFactory;

public class MainApp {
   public static void main(String[] args) {
      ApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml");

      Student student = (Student) context.getBean("student");

      //Create the Proxy Factory
      AspectJProxyFactory proxyFactory = new AspectJProxyFactory(student);

      //Add Aspect class to the factory
      proxyFactory.addAspect(Logging.class);

      //Get the proxy object
      Student proxyStudent = proxyFactory.getProxy();

      //Invoke the proxied method.
      proxyStudent.getAge();
   }
}

以下是配置文件Beans.xml的内容。

<?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"
   xsi:schemaLocation = "http://www.springframework.org/schema/beans
   http://www.springframework.org/schema/beans/spring-beans-3.0.xsd 
   http://www.springframework.org/schema/aop 
   http://www.springframework.org/schema/aop/spring-aop-3.0.xsd ">

   <!-- Definition for student bean -->
   <bean id = "student" class = "com.tutorialspoint.Student">
      <property name = "age"  value = "11"/>      
   </bean>

   <!-- Definition for logging aspect -->
   <bean id = "logging" class = "com.tutorialspoint.Logging"/> 
</beans>

运行项目

创建源文件和配置文件后，运行您的应用程序。右键单击应用程序中的MainApp.java，并使用以Java应用程序运行命令。如果应用程序一切正常，它将打印以下消息。

Going to setup student profile.
Age : 11