How to Inject Set Collection using Spring dependency injection by Setter method? | Spring Tutorial

Enjoying This Tutorial?

Subscribe to Ram N Java for high-quality, practical Java and Spring tutorials!

SUBSCRIBE NOW

Introduction

In Spring Framework, injecting collections is a common design pattern for managing lists, sets, and maps without writing boilerplate code. When your application requires a collection of distinct literal values (such as strings, integers, or codes) where duplicates should be disregarded, Spring provides the dedicated <set> element to inject a java.util.Set via setter-based dependency injection.

Why Inject a Set Collection in Spring?

• Ensures Data Uniqueness: A Set automatically suppresses duplicate entries, ensuring your bean works strictly with unique elements.
• Declarative XML Configuration: The <set> and <value> tags make it straightforward to configure collection values in your XML configuration file.
• Loosely Coupled Design: Changing or extending the configured values requires only editing your Spring XML without modifying the underlying Java classes.

Step-by-Step Code Example

Here is an example showing how to inject a Set<String> of phone numbers into a Customer bean using setter injection:

1. The Java Model Class

package com.ram.model;

import java.util.Set;

public class Customer {
    private String name;
    private Set<String> phoneNumbers;

    public void setName(String name) {
        this.name = name;
    }

    // Setter method for Set injection
    public void setPhoneNumbers(Set<String> phoneNumbers) {
        this.phoneNumbers = phoneNumbers;
    }

    public void display() {
        System.out.println("Customer Name: " + name);
        System.out.println("Phone Numbers: " + phoneNumbers);
    }
}

2. Configuring applicationContext.xml

Inside the <property> element, define the values using the <set> and <value> tags:

<bean id="customer" class="com.ram.model.Customer">
    <property name="name" value="Ram" />
    <property name="phoneNumbers">
        <set>
            <value>9876543210</value>
            <value>9123456780</value>
            <value>9876543210</value> <!-- Duplicate values are eliminated -->
        </set>
    </property>
</bean>

3. Loading and Executing with ApplicationContext

ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");

Customer customer = (Customer) context.getBean("customer");
customer.display();

Key Takeaway

Spring handles the instantiation and population of java.util.Set collections seamlessly using the <set> element, allowing you to pass unique configuration values cleanly via setter dependency injection.

Recommended Collection & Dependency Injection Tutorials from Ram N Java

• How to Inject Set having Dependent Object using Spring dependency injection by Setter method?
• How to Inject Map using Spring dependency injection by Setter method? | Spring Tutorial
• How to Inject Array of String using Spring dependency injection by Setter method? | Spring Tutorial

---

Click here to watch on Youtube:
https://www.youtube.com/watch?v=bRtnP9hl9bc&list=UUhwKlOVR041tngjerWxVccw

Click the below Image to Enlarge:

How to Inject Set Collection using Spring dependency injection by Setter method? | Spring Tutorial

How to Inject Set Collection using Spring dependency injection by Setter method? | Spring Tutorial

How to Inject Set Collection using Spring dependency injection by Setter method? | Spring Tutorial

How to Inject Set Collection using Spring dependency injection by Setter method? | 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>

FruitShop.java

package com.ram.core;

import java.util.Set;

public class FruitShop
{
    private String shopName;
    private Set<String> availableFruitsSet;

    public String getShopName()
    {
        return shopName;
    }

    public void setShopName(String shopName)
    {
        System.out.println("setShopName(String shopName) is "
                + "called by the Spring Container");
        this.shopName = shopName;
    }

    public Set<String> getAvailableFruitsSet()
    {
        return availableFruitsSet;
    }

    public void setAvailableFruitsSet(Set<String> availableFruitsSet)
    {
        System.out.println(
                "setAvailableFruitsSet(Set<String> availableFruitsSet) is "
                        + "called by the Spring Container");
        this.availableFruitsSet = availableFruitsSet;
    }

    public void displayFruitShopInfo()
    {
        System.out.println("FruitShop [shopName=" + shopName
                + ", availableFruitsSet=" + availableFruitsSet + "]");
    }

}

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="fruitShop" class="com.ram.core.FruitShop">
       
        <property name="shopName" value="Fruit Mart"></property>
        <property name="availableFruitsSet">
            <set>
                <value>apple</value>
                <value>pineapple</value>
                <value>orange</value>
            </set>
        </property>

    </bean>

</beans>

App.java

package com.ram.core;

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

public class App
{
    public static void main(String[] args)
    {
        ApplicationContext context = new ClassPathXmlApplicationContext(
                "applicationContext.xml");

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

        FruitShop fruitShop = (FruitShop) context.getBean("fruitShop");
        System.out.println(
                "Got fruitShop object from the ApplicationContext(SpringContainer)");
        fruitShop.displayFruitShopInfo();

    }

}

Output

May 12, 2018 8:55:28 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Sat May 12 08:55:28 IST 2018]; root of context hierarchy
May 12, 2018 8:55:28 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [applicationContext.xml]
setShopName(String shopName) is called by the Spring Container
setAvailableFruitsSet(Set<String> availableFruitsSet) is called by the Spring Container
---------------------------------------
Got fruitShop object from the ApplicationContext(SpringContainer)
FruitShop [shopName=Fruit Mart, availableFruitsSet=[apple, pineapple, orange]]