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How to provide default constructor initialization to a bean using Spring Framework ?.


A simple example to demonstrate, how to provide default constructor initialization of a bean using Spring xml configuration file in Spring Framework

Scenario 1 : Default Constructor

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

package com.hubberspot.spring;


public class Dog {

 private String breed;
 private int teeth;

 // Scenario 1 : Default Constructor
 public Dog(){
  this.breed = "shepherd";
  this.teeth = 20;
 }

 // Generating getters and setters
 // for all the properties of Dog

 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 -


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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">

  <!-- default constructor will be called -->

 </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 dog = (Dog)context.getBean("dog");

  // Calling our functionality
  dog.move();

 }

}



Output of the program :





Video tutorial to demonstrate how to configure beans in Spring configuration file






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