Spring tutorial 05- Initializing and injecting value in Bean property

To start this blog, lets understand the Beans.

The beans:

A Spring IoC container manages one or more beans. These beans are created using the configuration metadata that has been supplied to the container (typically in the form of XML <bean/> definitions). Beans are represented as beanDefintion objects which contains following meadata.

• a package-qualified class name: typically this is the actual implementation class of the bean being defined.
• bean behavioral configuration elements, which state how the bean should behave in the container (scope, lifecycle callbacks, and so forth).
• references to other beans which are needed for the bean to do its work; these references are also called collaborators or dependencies.
• other configuration settings to set in the newly created object. An example would be the number of connections to use in a bean that manages a connection pool, or the size limit of the pool.

In Spring, InitializingBean is a marker interface, which is used to initialize the bean.

• For bean implemented InitializingBean, it will run afterPropertiesSet() after all bean properties have been set

• For bean implemented DisposableBean, it will run destroy() after Spring container is released the bean.

Example :

In below example we can see, how property can be initialized.

Let's create a project say "SpringTutorial" now add the required jar support to spring, to add the jar  you can follow the Spring Tutorial 02 -My First 'Hello World' Program in Spring blog

Now create a package with the name of "org.javaIsEasy.springPropertyInitializationExample".

Create a java file in this package with the name of "Area.java".

Area.java

*******************************************************************************

package org.javaIsEasy.springPropertyInitializationExample;

public class Area {

private String areaOf;

 public String getAreaOf() {

 return areaOf;

}

public void setAreaOf(String areaOf) {

 this.areaOf = areaOf;

}

 public void calculateArea()

 {

  System.out.println(getAreaOf()+" Area Has been calculated");

 }

}

*******************************************************************************

Now create another file in the same folder with the name of "CallAreaApplication.java".

CallAreaApplication.java

*******************************************************************************

package org.javaIsEasy.springPropertyInitializationExample;

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class CallAreaApplication {

public static void main(String[] args) {

 ApplicationContext context=new ClassPathXmlApplicationContext("org/javaIsEasy/springPropertyInitializationExample/Beans.xml");

 Area area=(Area)context.getBean("area");

 area.calculateArea();

}

}

*******************************************************************************

Now at last one more file is need to be created in which we define beans, so let's create "Beans.xml" file in the same folder again.

Beans.xml 

*******************************************************************************

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

    xsi:schemaLocation="http://www.springframework.org/schema/beans

    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

   <bean id="area" class="org.javaIsEasy.springPropertyInitializationExample.Area">

      <property name="areaOf" value="Rectangle"></property>

   </bean>

</beans>

*******************************************************************************

in the above xml file we have injecting the value to the "areaOf" object of the Area class, and giving the value of "Rectangle".

Structure of the project :

Lets run this program to get the result:

Output:

*******************************************************************************

Rectangle Area Has been calculated

*******************************************************************************