Spring Constructor DI – Injecting Primitive and String-based values

In this tutorial we are going to see about Spring Dependency Injection to inject Primitive and String based values using Constructor-Injection.
Note : JavaBeans PropertyEditors are used to convert the string values from a String to the actual type of the property or argument.
Step by step procedure to create Spring Program using Eclipse given below.
Follow the Simple steps.
1. Select File –> New –> Java Project from your Eclipse IDE.
2.Create project called SpringConstructorDI.
3. Add the following jars into your build path.

commons-logging-1.1.3.jar
spring-beans-3.2.6.RELEASE.jar
spring-context-3.2.6.RELEASE.jar
spring-context-support-3.2.6.RELEASE.jar
spring-core-3.2.6.RELEASE.jar
spring-expression-3.2.6.RELEASE.jar

4. Now create package com.javatutorialscorner.spring under SpringConstructorDI Project
5. Next create PrimitiveConstructorDI class under com.javatutorialscorner.spring package
PrimitiveConstructorDI.java

package com.javatutorialscorner.spring;

public class PrimitiveConstructorDI {
 private int id;
 private String name;
 private String job;
 private double salary;

 PrimitiveConstructorDI(int id, String name, String job, double salary) {
  System.out.println("Inside PrimitiveConstructorDI() Constructor");
  this.id = id;
  this.name = name;
  this.job = job;
  this.salary = salary;
 }

 public void getDetail() {
  System.out.println("int value ID :" + id);
  System.out.println("String value name :" + name);
  System.out.println("String value job :" + job);
  System.out.println("double value salary :" + salary);
 }

}

6. Now Create RunApp class which contains Bean configuration path to load configuration from Bean.xml file

RunApp.java

package com.javatutorialscorner.spring;

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

public class RunApp {

 /**
  * @param args
  */
 public static void main(String[] args) {
  // TODO Auto-generated method stub

  ApplicationContext context = new ClassPathXmlApplicationContext(
    "Beans.xml");
  PrimitiveConstructorDI constructorDI = (PrimitiveConstructorDI) context
    .getBean("constructorDI");
  constructorDI.getDetail();
  
 }

}

In above program

First step I created Application context using ClassPathXmlApplicationContext which load configuration from bean file which located in class path of application, It take care of creating and initializing all the objects (Beans) declared in bean.xml

Next getBean() method used to get particular bean from created context. This method used bean name as parameter and returns generic object. We can caste to actual object.

Once Object Created you can access any method from that class.

7. Create Bean.xml at where your class files created (ClassPathXmlApplicationContext tries to load bean file from class path).

Bean.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.xsd">

 <bean id="constructorDI" class="com.javatutorialscorner.spring.PrimitiveConstructorDI">
  <constructor-arg name="id" value="5005" />
  <constructor-arg name="name" value="Appu.T" />
  <constructor-arg name="job" value="Software Engineer" />
  <constructor-arg name="salary" value="45000.00" />
 </bean>


</beans>

The value attribute of the <constructor-arg/> element specifies a property or constructor argument as a human-readable string representation. JavaBeans PropertyEditors are used to convert these string values from a String to the actual type of the property or argument

Bean.xml is default name given to bean configuration file. You can choose any name for your bean.xml but you can use file name in main application to create context and your file available in your class path must be same.

Bean.xml is used to assign unique ID to different beans and controls the creation object with different values, using above file you can pass any value to variables without changing the class file.

Now you can run the program see the following output in console.

Inside PrimitiveConstructorDI() Constructor
int value ID :5005
String value name :Appu.T
String value job :Software Engineer
double value salary :45000.0