How to Inject primitive value using Spring dependency injection by constructor? | Spring Tutorial

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Introduction

In Spring Framework, Constructor Injection is one of the most reliable approaches to initialize beans because it ensures all mandatory fields—including simple types like numbers and text—are supplied when the object is instantiated.

In this guide, you will learn how to configure Spring XML to inject a primitive data type (such as int, double, or long) using constructor dependency injection.

1. Create the Java Bean Class

Create a model class named Employee that contains a primitive field along with a matching constructor:

public class Employee {
    private int id;

    public Employee(int id) {
        this.id = id;
    }

    public void displayEmployeeInfo() {
        System.out.println("Employee ID: " + id);
    }
}
  

2. Configure Spring XML with <constructor-arg>

In your applicationContext.xml, declare the bean and define the argument using <constructor-arg>. You can specify the type="int" attribute to ensure precise type matching:

<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="employeeBean" class="Employee">
        <constructor-arg type="int" value="101" />
    </bean>

</beans>
  

3. Load Context and Run the Application

Initialize the Spring IoC container with ClassPathXmlApplicationContext, get the bean, and display the initialized values:

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

public class MainApp {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        Employee emp = (Employee) context.getBean("employeeBean");
        emp.displayEmployeeInfo();
    }
}
  

Watch More Spring Tutorials

• How to Inject String value using Spring dependency injection by constructor? | Spring Tutorial
• How to Inject primitive value and String using Spring dependency injection by constructor?
• Understanding Constructor Injection Type Ambiguities in Spring | Spring Framework Explained

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How to Inject primitive value using Spring dependency injection by constructor? | Spring Tutorial

How to Inject primitive value using Spring dependency injection by constructor? | Spring Tutorial

How to Inject primitive value using Spring dependency injection by constructor? | Spring Tutorial

How to Inject primitive value using Spring dependency injection by constructor? | Spring Tutorial