Dependency Injection via Constructor in spring

This is 7 of 16 parts of tutorial series

Tutorial Content: Spring tutorial for beginners

As the name implies, using constructor spring container will inject the dependencies.
For configuring spring in your eclipse ide please refer hello world example

Dependency Injection via Constructor

1.Country.java:

We will create a simple class which has countryName and capital as attributes.

Create Country.java under package org.arpit.java2blog.Copy following content into Country.java.

package org.arpit.java2blog;

public class Country {

String countryName;

Capital capital;

public Country(String countryName, Capital capital) {

super();

this.countryName = countryName;

this.capital = capital;

}

public String getCountryName() {

return countryName;

}

public Capital getCapital() {

return capital;

}

2.Capital.java

Create Capital.java under package org.arpit.java2blog.Above Country class contains object of this class.Copy following content into Capital.java

package org.arpit.java2blog;

public class Capital {

String capitalName;

public String getCapitalName() {

return capitalName;

}

public void setCapitalName(String capitalName) {

this.capitalName = capitalName;

}

3.ApplicationContext.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" xmlns:aop="http://www.springframework.org/schema/aop"

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

<constructor-arg index="0" type="java.lang.String" value="India" />

<constructor-arg index="1" ref="CaptialBean" />

</bean>

</bean>

</beans>

Here We have declared two beans with corresponding ids.
1.Class Country with id as “CountryBean”
2.Class Capital with id as “CapitalBean”
constructor-arg tag is used for providing argument to bean’ s constructor.type is for declaring data types and index defines position in constructor’s argument.
In above xml,Two arguments are passed.
1. India as string
2.CapitalBean ‘s reference
Property’s value tag is for assigning value to corresponding attribute. so In above xml file,we have assigned capitalName attribute of Capital class with value as Delhi

Property’s ref tag is used for assigning reference to the corresponding attribute. so In above xml file, we have assigned reference of Capital class to capital attribute of Country class.

4.ConstructorDIMain.java

This class contains main function.Create ConstructorDIMain.java under package org.arpit.java2blog.

package org.arpit.java2blog;

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

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import org.springframework.core.io.ClassPathResource;

public class ConstructorDIMain{

public static void main(String[] args) {

ApplicationContext appContext = new ClassPathXmlApplicationContext("ApplicationContext.xml");

Country countryObj = (Country) appContext.getBean("CountryBean");

String countryName=countryObj.getCountryName();

String capitalName=countryObj.getCapital().getCapitalName();

System.out.println(capitalName+" is capital of "+countryName);

}

You can note here that we have used ClassPathXmlApplicationContext for getting bean here.There are various ways for getting beans.In hello world example we have used XmlBeanFactory for getting beans.