How to Inject List having Dependent Object using Spring dependency injection by constructor?

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Introduction

In Spring Framework applications, configuring collections containing custom objects is a regular requirement. Using constructor injection ensures that your bean is initialized with all its required collection elements in an immutable, ready-to-use state.

In this guide, you will learn how to inject a List containing Dependent Objects into a bean through its constructor using Spring XML configuration.

1. Create the Dependent Class (Fruit)

First, define the dependent class Fruit which holds attributes such as fruit name and color:

public class Fruit {
    private String fruitName;
    private String color;

    public Fruit(String fruitName, String color) {
        this.fruitName = fruitName;
        this.color = color;
    }

    @Override
    public String toString() {
        return "Fruit [fruitName=" + fruitName + ", color=" + color + "]";
    }
}
  

2. Create the Target Class (FruitShop)

Create the target class FruitShop that accepts a List<Fruit> through its constructor:

import java.util.List;

public class FruitShop {
    private String shopName;
    private List<Fruit> fruitList;

    public FruitShop(String shopName, List<Fruit> fruitList) {
        this.shopName = shopName;
        this.fruitList = fruitList;
    }

    public void displayFruitShopInfo() {
        System.out.println("Shop Name: " + shopName);
        System.out.println("Fruit Inventory:");
        for (Fruit fruit : fruitList) {
            System.out.println(" - " + fruit);
        }
    }
}
  

3. Configure Spring XML with <list> and <ref>

In your applicationContext.xml, declare the Fruit beans, and then reference them inside the <list> element inside <constructor-arg> using <ref bean="..." />:

<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">

    <!-- Dependent Beans -->
    <bean id="appleBean" class="Fruit">
        <constructor-arg value="Apple" />
        <constructor-arg value="Red" />
    </bean>

    <bean id="mangoBean" class="Fruit">
        <constructor-arg value="Mango" />
        <constructor-arg value="Yellow" />
    </bean>

    <!-- Target Bean -->
    <bean id="fruitShop" class="FruitShop">
        <constructor-arg value="Organic Fruit Bazaar" />
        <constructor-arg>
            <list>
                <ref bean="appleBean" />
                <ref bean="mangoBean" />
            </list>
        </constructor-arg>
    </bean>

</beans>
  

4. Run and Test the Code

Load the application context and execute your program to see the list of dependent beans injected:

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");
        FruitShop shop = (FruitShop) context.getBean("fruitShop");
        shop.displayFruitShopInfo();
    }
}
  

Watch More Spring Tutorials

• How to Inject List Collection using Spring dependency injection by constructor? | Spring Tutorial
• How to Inject Set having Dependent Object using Spring dependency injection by constructor?
• How to Inject Dependent Object using Spring dependency injection by constructor? | Spring Tutorial

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How to Inject List having Dependent Object using Spring dependency injection by constructor?

How to Inject List having Dependent Object using Spring dependency injection by constructor?

How to Inject List having Dependent Object using Spring dependency injection by constructor?

How to Inject List having Dependent Object using Spring dependency injection by constructor?