How to use aliases when referring to a bean in configuration file of Spring Framework ?.

A simple example to demonstrate, how to use Aliases when referring to a bean configuration file in Spring Framework

1. Create a Dog class

package com.hubberspot.spring;


public class Dog {

 private String tail;
 private String coat;
 private String breed;

 public String getTail() {
  return tail;
 }

 public void setTail(String tail) {
  this.tail = tail;
 }

 public String getCoat() {
  return coat;
 }

 public void setCoat(String coat) {
  this.coat = coat;
 }

 public String getBreed() {
  return breed;
 }

 public void setBreed(String breed) {
  this.breed = breed;
 }

 public void move() {
  System.out.println("A Dog of breed "+ getBreed() +", " +
    "having "+ getCoat() +"\nand "+ getTail() + " " +
    "tail moves slowly ...");
 }


}


2. Create a Spring configuration file say spring.xml and place it in classpath i.e src folder of your Eclipse



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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN" 
"http://www.springframework.org/dtd/spring-beans-2.0.dtd">

<beans>

 <!-- In order to create an object of bean we define its properties in bean 
  tag. The 'id' attribute value can be thought of as a reference to 'class' 
  attribute value -->

 <bean id="dog" class="com.hubberspot.spring.Dog">


  <!-- setting the property of dog from the spring configuration file, the 
   property tag uses the setter method to set the properties to its respective 
   field -->

  <property name="tail" value="straight"></property>
  <property name="coat" value="stripes on white fur"></property>
  <property name="breed" value="German Shepherd"></property>

 </bean>

 <!-- here name is mapped with the id of the bean and alias is the new name 
  designers provide as per requirement -->
 <alias name="dog" alias="dog-alias" />


</beans>

3. Create a test class and run to see the output below : 

package com.hubberspot.spring;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;


public class WildLifeApplication {

 public static void main(String[] args) {

  // ApplicationContext is a Spring interface which 
  // provides with the configuration for an application. 
  // It provides us with all the methods that BeanFactory 
  // provides. It loads the file resources in a older 
  // and generic manner. It helps us to publish events to the
  // listener registered to it. It also provides quick support
  // for internationalization. It provides us with the object 
  // requested, it reads the configuration file and provides
  // us with the necessary object required.
  // We are using concrete implementation of ApplicationContext
  // here called as ClassPathXmlApplicationContext because this 
  // bean factory reads the xml file placed in the classpath of 
  // our application. We provide ClassPathXmlApplicationContext
  // with a configuration file called as spring.xml placed
  // at classpath of our application. 
  ApplicationContext context = 
    new ClassPathXmlApplicationContext(("spring.xml"));

  // In order to get a object instantiated for a particular bean 
  // we call getBean() method of ClassPathXmlApplicationContext
  // passing it the id for which the object is to be needed. 
  // Here getBean() returns an Object. We need to cast it back 
  // to the Dog object. Without implementing new keyword we 
  // have injected object of Dog just by reading an xml 
  // configuration file.
  Dog dog = (Dog)context.getBean("dog");

  // Calling our functionality
  dog.move();
  
  // getting the same bean of dog by calling the alias of dog
  // alias help us by providing different name to a single
  // bean as per our design needs.
  // check for changes done in spring.xml file
  dog = (Dog)context.getBean("dog-alias");

  // Calling our functionality
  dog.move();

 }

}



Output of the program :