Spring AOP

Aspect-Oriented Programming (AOP) complements Object-Oriented Programming (OOP) by providing another way of thinking about program structure. The key unit of modularity in OOP is the class, whereas in AOP the unit of modularity is the aspect. Aspects enable the modularization of concerns such as transaction management that cut across multiple types and objects. (Such concerns are often termed crosscutting concerns in AOP literature.)

AOP concepts

Let us begin by defining some central AOP concepts and terminology. These terms are not Spring-specific... unfortunately, AOP terminology is not particularly intuitive; however, it would be even more confusing if Spring used its own terminology.

• Aspect: a modularization of a concern that cuts across multiple classes. Transaction management is a good example of a crosscutting concern in enterprise Java applications. In Spring AOP, aspects are implemented using regular classes (the schema-based approach) or regular classes annotated with the @Aspect annotation (the @AspectJ style).
• Join point: a point during the execution of a program, such as the execution of a method or the handling of an exception. In Spring AOP, a join point always represents a method execution.
• Advice: action taken by an aspect at a particular join point. Different types of advice include "around," "before" and "after" advice. (Advice types are discussed below.) Many AOP frameworks, including Spring, model an advice as an interceptor, maintaining a chain of interceptors around the join point.
• Pointcut: a predicate that matches join points. Advice is associated with a pointcut expression and runs at any join point matched by the pointcut (for example, the execution of a method with a certain name). The concept of join points as matched by pointcut expressions is central to AOP, and Spring uses the AspectJ pointcut expression language by default.
• Introduction: declaring additional methods or fields on behalf of a type. Spring AOP allows you to introduce new interfaces (and a corresponding implementation) to any advised object. For example, you could use an introduction to make a bean implement an IsModified interface, to simplify caching. (An introduction is known as an inter-type declaration in the AspectJ community.)
• Target object: object being advised by one or more aspects. Also referred to as the advised object. Since Spring AOP is implemented using runtime proxies, this object will always be a proxied object.
• AOP proxy: an object created by the AOP framework in order to implement the aspect contracts (advise method executions and so on). In the Spring Framework, an AOP proxy will be a JDK dynamic proxy or a CGLIB proxy.
• Weaving: linking aspects with other application types or objects to create an advised object. This can be done at compile time (using the AspectJ compiler, for example), load time, or at runtime. Spring AOP, like other pure Java AOP frameworks, performs weaving at runtime.

Types of advice:

• Before advice: Advice that executes before a join point, but which does not have the ability to prevent execution flow proceeding to the join point (unless it throws an exception).
• After returning advice: Advice to be executed after a join point completes normally: for example, if a method returns without throwing an exception.
• After throwing advice: Advice to be executed if a method exits by throwing an exception.
• After (finally) advice: Advice to be executed regardless of the means by which a join point exits (normal or exceptional return).
• Around advice: Advice that surrounds a join point such as a method invocation. This is the most powerful kind of advice. Around advice can perform custom behavior before and after the method invocation. It is also responsible for choosing whether to proceed to the join point or to shortcut the advised method execution by returning its own return value or throwing an exception.
  
  
  Source : http://docs.spring.io/spring/docs/3.0.x/reference/aop.html
  
  
  Example :-
  
  

  Simple class
  

  package com.deepak.pojo;
  /**
   * @author deepak
   * 
   */
  public class Student {
   private int roll;
   private String name;
  
   public int getRoll() {
    return roll;
   }
  
   public void setRoll(int roll) {
    this.roll = roll;
   }
  
   public String getName() {
    return name;
   }
  
   public void setName(String name) {
    this.name = name;
   }
  
   public void printName(String name) {
    System.out.println("Name is : " + this.name);
   }
  
   public void printRoll() {
    System.out.println("Roll is : " + this.roll);
   }
  
   public void throwExcetion() {
    throw new IllegalArgumentException("Checking the exception");
   }
  
   @Override
   public String toString() {
    return "name = " + this.name + " roll = " + this.roll;
   }
  }
  

Around Advice

package com.deepak.advice;

import java.util.Arrays;

import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;

/**
 * @author deepak
 * 
 */
public class MethodAround implements MethodInterceptor {

 public Object invoke(MethodInvocation method) throws Throwable {
  System.out.println("Method name : " + method.getMethod().getName());
  System.out.println("Method arguments : "
    + Arrays.toString(method.getArguments()));
  System.out.println("Called before method call");
  try {
   Object result = method.proceed();
   System.out.println("Called after method call");
   return result;
  } catch (Exception e) {
   System.out.println("Called before exception handeling");
   throw e;
  }
 }
}

Main Class

package com.deepak.main;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.deepak.pojo.Student;

public class Main {

 /**
  * @param args
  */
 public static void main(String[] args) {
  ClassPathXmlApplicationContext appcontext = new ClassPathXmlApplicationContext(
    "appcontext.xml");
  Student s1 = (Student) appcontext.getBean("studentProxy");
  s1.printName("Argument to function");
  s1.printRoll();
  s1.throwExcetion();
  System.out.println(s1);
  appcontext.close();
 }

}

Spring configuration file

 
  
  
 
 
 
  
  
   
    methodAround
   
  
 

Download source code : https://github.com/cdeepakait/AOP.git