IOC

♠ Posted by Java Tutorials at 11:49 PM

                     
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Inversion Of Control (IOC) and Dependency Injection

These are the design patterns that are used to remove dependency from the programming code. They make the code easier to test and maintain. Let's understand this with the following code:

class Employee{

Address address;Employee()

{address=new Address();

}

}

In such case, there is dependency between the Employee and Address (tight coupling). In the Inversion of Control scenario, we do this something like this:

class Employee{

Address address;

Employee(Address address){

this.address=address;

}

}

Thus, IOC makes the code loosely coupled. In such case, there is no need to modify the code if our logic is moved to new environment.

In Spring framework, IOC container is responsible to inject the dependency. We provide metadata to the IOC container either by XML file or annotation.

Advantage of Dependency Injection

·         makes the code loosely coupled so easy to maintain

·         makes the code easy to test

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Steps to create spring application

1. Steps to create spring application

Here, we are going to learn the simple steps to create the first spring application. To run this application, we are not using any IDE. We are simply using the command prompt. Let's see the simple steps to create the spring application

§  create the class

§  create the xml file to provide the values

§  create the test class

§  Load the spring jar files

§  Run the test class

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Steps to create spring application

Let's see the 5 steps to create the first spring application.

1) Create Java class

This is the simple java bean class containing the name property only.

package org.sample;

public class Student {

private String name;

public String getName() {

return name;

}

public void setName(String name) {

            this.name = name;

}

public void displayInfo(){

            System.out.println("Hello: "+name);

}

}

This is simple bean class, containing only one property name with its getters and setters method. This class contains one extra method named displayInfo() that prints the student name by the hello message.

2) Create the xml file

In case of myeclipse IDE, you don't need to create the xml file as myeclipse does this for yourselves. Open the applicationContext.xml file, and write the following code:

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

<beans

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

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

                 xmlns:p="http://www.springframework.org/schema/p"

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

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

<bean id="studentbean" class="org.sample.Student">

<property name="name" value="Venkata"></property>

</bean>

</beans>

The bean element is used to define the bean for the given class. The property subelement of bean specifies the property of the Student class named name. The value specified in the property element will be set in the Student class object by the IOC container.

3) Create the test class

Create the java class e.g. Test. Here we are getting the object of Student class from the IOC container using the getBean() method of BeanFactory. Let's see the code of test class.

package org.sample;

import org.springframework.beans.factory.BeanFactory;

import org.springframework.beans.factory.xml.XmlBeanFactory;

import org.springframework.core.io.ClassPathResource;

import org.springframework.core.io.Resource;

public class Test {

public static void main(String[] args) {

                 Resource resource=new ClassPathResource("applicationContext.xml");

                 BeanFactory factory=new XmlBeanFactory(resource);

                 Student student=(Student)factory.getBean("studentbean");

                 student.displayInfo();

}

}

The Resource object represents the information of applicationContext.xml file. The Resource is the interface and the ClassPathResource is the implementation class of the Reource interface. TheBeanFactory is responsible to return the bean. The XmlBeanFactory is the implementation class of the BeanFactory. There are many methods in the BeanFactory interface. One method is getBean(), which returns the object of the associated class.

4) Load the jar files required for spring framework

There are mainly three jar files required to run this application.

·         org.springframework.core-3.0.1.RELEASE-A

·         com.springsource.org.apache.commons.logging-1.1.1

·         org.springframework.beans-3.0.1.RELEASE-A

For the future use, You can download the required jar files for spring core application.

To run this example, you need to load only spring core jar files.

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