Spring AOP - Proxy

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So far, we've declared aspects using <aop:config> or < aop:aspectj-autoproxy>. We can create a proxy programmatically as well as invoke the aspects programmatically using the proxy object.

Syntax

//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();

Where,

  • AspectJProxyFactory − Factory class to create a proxy object.

  • Logging.class − Class of the Aspect containing advices.

  • Student − Business class to be advised.

To understand the above-mentioned concepts related to proxy, let us write an example which will implement proxy. To write our example with few advices, let us have a working Eclipse IDE in place and use the following steps to create a Spring application −

Step Description
1 Update the project Student created under chapter Spring AOP - Application.
2 Update the bean configuration and run the application as explained below.

Following is the content of Logging.java file. This is actually a sample of aspect module, which defines the methods to be called at various points.

package com.howcodex;

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.howcodex.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.");
   }  
}

Following is the content of the Student.java file.

package com.howcodex;

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

Following is the content of the MainApp.java file.

package com.howcodex;

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();
 
   }
}

Following is the configuration file 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"
   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.howcodex.Student">
      <property name = "age"  value = "11"/>      
   </bean>

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

Run Project

Once you are done creating the source and configuration files, run your application. Rightclick on MainApp.java in your application and use run as Java Application command. If everything is fine with your application, it will print the following message.

Going to setup student profile.
Age : 11
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