JAVA EE: String Injection

Showing posts with label String Injection. Show all posts

Friday, 25 May 2018

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

Enjoying this Java & Spring tutorial?

Introduction

In Spring Framework, Constructor Injection is one of the most fundamental ways to pass required configuration data into your beans upon instantiation. When working with literal text values like names, identifiers, or URLs, passing a String directly through the constructor guarantees that the bean is initialized with all its required state.

In this beginner-friendly tutorial, you will learn how to configure Spring XML to inject a simple String value into a Java class using constructor-based dependency injection.

1. Create the Java Bean Class

First, create a Java class (for instance, Employee) that has a String member variable and a constructor that accepts this parameter:

public class Employee {
    private String name;

    public Employee(String name) {
        this.name = name;
    }

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

2. Configure Spring XML with <constructor-arg>

In your Spring configuration file (applicationContext.xml), define the bean and pass the String value using the <constructor-arg> element. You can optionally specify type="java.lang.String" for clarity:

<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="java.lang.String" value="Peter" />
    </bean>

</beans>

3. Run and Verify the Output

Load the Spring application context using ClassPathXmlApplicationContext, fetch your bean, and call the display method:

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

Click here to watch on Youtube:
https://www.youtube.com/watch?v=w7iXXCrD0pQ&list=UUhwKlOVR041tngjerWxVccw

Click the below Image to Enlarge:

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

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0%20http://maven.apache.org/maven-v4_0_0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <groupId>com.ram.core</groupId>

    <artifactId>SpringDemo</artifactId>

    <packaging>jar</packaging>

    <version>1.0-SNAPSHOT</version>

    <name>SpringDemo</name>

    <url>http://maven.apache.org</url>

    <properties>

        <spring.version>5.0.2.RELEASE</spring.version>

    </properties>

    <dependencies>

        <dependency>

            <groupId>junit</groupId>

            <artifactId>junit</artifactId>

            <version>3.8.1</version>

            <scope>test</scope>

        </dependency>

        <!-- Spring 5 dependencies -->

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-core</artifactId>

            <version>${spring.version}</version>

        </dependency>

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-context</artifactId>

            <version>${spring.version}</version>

        </dependency>

    </dependencies>

</project>

Employee.java

package com.ram.model;

public class Employee

{

    private int id;

    private String name;

    public Employee(int id)

    {

        System.out.println("Employee(int id) constructor is called "

                + "by the Spring container");

        this.id = id;

    }

    public Employee(String name)

    {

        System.out.println("Employee(String name) constructor is called "

                + "by the Spring container");

        this.name = name;

    }

    public Employee(int id, String name)

    {

        System.out.println("Employee(int id, String name) constructor "

                + "is called by the Spring container");

        this.id = id;

        this.name = name;

    }

    public void displayEmployeeDetails()

    {

        System.out.println("Employee [id=" + id + ", name=" + name + "]");

    }

}

applicationContext.xml

<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-4.3.xsd">

    <bean id="employee" class="com.ram.model.Employee">

        <constructor-arg  type="String" value="Peter"></constructor-arg>

    </bean>

</beans>

App.java

package com.ram.core;

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.ram.model.Employee;

public class App

{

    public static void main(String[] args)

    {

        ApplicationContext context = new ClassPathXmlApplicationContext(

                "applicationContext.xml");

        System.out.println("---------------------------------------");

        Employee employee = (Employee) context.getBean("employee");

        System.out.println(

                "Got employee object from the ApplicationContext(Spring Container)");

        employee.displayEmployeeDetails();

    }

}

Output

Apr 16, 2018 8:16:12 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Mon Apr 16 08:16:12 IST 2018]; root of context hierarchy

Apr 16, 2018 8:16:12 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions

INFO: Loading XML bean definitions from class path resource [applicationContext.xml]

Employee(String name) constructor is called by the Spring container

---------------------------------------

Got employee object from the ApplicationContext(Spring Container)

Employee [id=0, name=Peter]