How to provide constructor initialization to a bean using type attribute in configuration file of Spring Framework ?.

A simple example to demonstrate, how to provide constructor initialization to a bean using constructor-arg tag's type attribute in configuration file of Spring Framework


1. Create a normal class having constructor say 'Dog' -

package com.hubberspot.spring;


public class Dog {

 private String breed;
 private int teeth;

 // Overloaded Constructor
 public Dog(String breed, int teeth){
  this.breed = breed;
  this.teeth = teeth;
 }

 // Overloaded Constructor
 public Dog(String breed, String teeth){
  this.breed = breed;
  this.teeth = teeth.equals("twenty") ? 20 : 0;
 }

 public int getTeeth() {
  return teeth;
 }


 public void setTeeth(int teeth) {
  this.teeth = teeth;
 }


 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 "+ getTeeth() +" teeth moves slowly ...");
 }

}

2. Create a spring.xml file placed in classpath of your application -

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. <?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="shepherd" class="com.hubberspot.spring.Dog"> <!-- Here in the constructor-arg tag, in order to resolve the constructor calling ambiguity by Spring we provide the type attribute which takes full package name in case of any object and primitive type if its primitive value --> <constructor-arg type="int" value="20"></constructor-arg> <constructor-arg type="java.lang.String" value="shepherd"></constructor-arg> </bean> <bean id="germanShepherd" class="com.hubberspot.spring.Dog"> <constructor-arg type="java.lang.String" value="shepherd"></constructor-arg> <constructor-arg type="java.lang.String" value="twenty"></constructor-arg> </bean> </beans>

3. Create a Test class for the application (imp) -

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 dog1 = (Dog)context.getBean("shepherd");
  Dog dog2 = (Dog)context.getBean("germanShepherd");

  // creating two Dog objects and implementing type attribute
  // of constructor-arg

  // Calling our functionality
  dog1.move();
  dog2.move();

 }

}

Output of the program :