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Coding is much easier than you think

Constructor injection in Spring – Example


Instead of using the setter methods to inject values to attributes, the constructor of a class can be used to inject the values from outside the class. This work again, is done through the spring metadata file , as is in the case of setter injection.

** UPDATE: Spring Complete tutorial now available here.

1. Create the POJO class into which values are to be injected using setter injection

File : SimpleConstructorInjection

package com.simpleCodeStuffs;

public class SimpleConstructorInjection {
public SimpleConstructorInjection(String message){

private String message;

public void setMessage(String message){

this.message = message;
public void getMessage(){
System.out.println("Your Message : " + message);


Note : Unlike setter injection, a constructor has to be explicitly defined for the POJO in case of constructor injection. This is because, usually a default(no parameter) constructor is taken up. But since we will be passing a value to the constructor of this POJO to instantiate it, we require a constructor whose parameters match the set of values passed from the xml.


2 Define the metadata

The value for the attribute of the POJO is provided as<constructor-arg value=” ” /> thereby setting the values of these attributes through the constructor.
File : Beans.xml


The values are injected into the POJO through the constructor of these classes


3. Write the main class to place a call to this POJO

File :

package com.simpleCodeStuffs;

import org.springframework.context.ApplicationContext;

public class MainClass {
public static void main(String[] args) {
ApplicationContext context =
new ClassPathXmlApplicationContext("Beans.xml");
SimpleConstructorInjection obj = 
(SimpleConstructorInjection) context.getBean("simpleConstructorInjection");



4. Run it

The output appears as :-



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