Spring Dependency Inject using Constructor

In Constructor based DI(Dependency Injection), Objects define their dependencies via Constructor argument(<constructor-arg> tag) and Container invoke Constructors to set these arguments in object.

Address Bean Class

package com.jbt.bean;

import java.util.List;

public class Address {

	public String flatNo;
	public String bldgNo;
	public String streetNo;
	public String city;
	public int pincode;

	public String getStreetNo() {
		return streetNo;
	}

	public void setStreetNo(String streetNo) {
		System.out.println("Setter method is called");
		this.streetNo = streetNo;
	}

	public String getFlatNo() {
		return flatNo;
	}

	public void setFlatNo(String flatNo) {
		this.flatNo = flatNo;
	}

	public String getBldgNo() {
		return bldgNo;
	}

	public void setBldgNo(String bldgNo) {
		this.bldgNo = bldgNo;
	}

	public String getCity() {
		return city;
	}

	public void setCity(String city) {
		this.city = city;
	}

	public int getPincode() {
		return pincode;
	}

	public void setPincode(int pincode) {
		this.pincode = pincode;
	}

	Address(String flatNo, String bldgNo, String streetNo, String city,
			int pincode) {
		super();
		System.out.println("Constructor with multiple argument invoked");
		this.flatNo = flatNo;
		this.bldgNo = bldgNo;
		this.streetNo = streetNo;
		this.city = city;
		this.pincode = pincode;
	}

	Address(List l1) {
		super();
		System.out.println("Constructor with Single List argument invoked");
		this.flatNo = (String) l1.get(0);
		this.bldgNo = (String) l1.get(1);
		this.streetNo = (String) l1.get(2);
		this.city = (String) l1.get(3);
		this.pincode = Integer.parseInt((String) l1.get(4));
	}

	@Override
	public String toString() {
		return "Address [flatNo=" + flatNo + ", bldgNo=" + bldgNo
				+ ", streetNo=" + streetNo + ", city=" + city + ", pincode="
				+ pincode + "]";
	}

}

Above Bean Class has two Constructor one with multiple argument for different property while other takes single argument as List.

Spring Configuration File

<?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-3.1.xsd">

	<!-- This is constructor injection. Constructor with List argument will
		be invoked -->
	<bean id="addressList" name="address1,address2" class="com.jbt.bean.Address">
		<constructor-arg>
			<list>
				<value>203</value>
				<value>2C</value>
				<value>JBT Street</value>
				<value>New York</value>
				<value>276001</value>
			</list>
		</constructor-arg>
	</bean>

	<!-- This is constructor injection. Constructor with multiple argument will
		be invoked -->
	<bean id="address" primary="true" class="com.jbt.bean.Address">
		<constructor-arg type="int" value="276044"></constructor-arg>
		<constructor-arg type="java.lang.String" value="My Street"></constructor-arg>
		<constructor-arg type="java.lang.String" value="My City"></constructor-arg>
		<constructor-arg type="java.lang.String" value="360"
			index="0"></constructor-arg>
		<constructor-arg type="java.lang.String" value="C2"
			index="1"></constructor-arg>
	</bean>

</beans>

Execute the Programme

package com.jbt;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.jbt.bean.Address;

/*
 * Here we will learn to Dependency Inject Bean with Setter Method.
 */
public class SpringDIConstructor {
	public static void main(String[] args) {

		ApplicationContext cpxac = new ClassPathXmlApplicationContext(
				"applicationContext_DIConstructor.xml");

		Address address = (Address) cpxac.getBean("address");

		/*
		 * address1 & address2 are the alias name for address id. Alias name can
		 * be defined in XML file using "name" attribute.
		 */
		Address address1 = (Address) cpxac.getBean("address1");

		Address address2 = (Address) cpxac.getBean("address2");

		System.out.println("This is address Bean :::::" + address.toString());
		System.out.println("This is address Bean :::::" + address1.toString());
		System.out.println("This is address Bean :::::" + address2.toString());

	}
}

Output of the above Application would be

Constructor with Single List argument invoked
Constructor with multiple argument invoked
This is address Bean :::::Address [flatNo=360, bldgNo=C2, streetNo=My Street, city=My City, pincode=276044]
This is address Bean :::::Address [flatNo=203, bldgNo=2C, streetNo=JBT Street, city=New York, pincode=276001]
This is address Bean :::::Address [flatNo=203, bldgNo=2C, streetNo=JBT Street, city=New York, pincode=276001]

Environment Used

Tool : Eclipse Indigo

Java : JDK 1.6

Spring : 3.1.1

Jars Required :

• org.springframework.core-3.1.1.RELEASE.jar
• org.springframework.context-3.1.1.RELEASE.jar
• org.springframework.asm-3.1.1.RELEASE.jar
• org.springframework.beans-3.1.1.RELEASE.jar
• org.springframework.expression-3.1.1.RELEASE.jar
• commong-logging-1.1.1.jar