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

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. <?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 :