JAVA EE: How to Inject Map using Spring dependency injection by Setter method?

Friday, 29 June 2018

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

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Introduction

In Spring Framework applications, configuring key-value pairs using collections is a common design pattern. When working with basic literal types (such as strings or primitive wrappers), Spring provides the dedicated <map> and <entry> XML elements to inject a java.util.Map into a bean via setter-based dependency injection.

Why Inject Map in Spring?

Key-Value Pair Support: Enables storing lookup tables, metadata, and dynamic configurations directly inside Spring-managed beans.
Declarative XML Configuration: Uses clear <entry key="..." value="..."/> tags to define and populate maps without writing Java boilerplate code.
Easy Maintenance: Centralizes key-value configurations inside the Spring XML file, making it simple to add, remove, or modify entries.

Step-by-Step Code Example

Here is an example demonstrating a Customer bean receiving a map of account numbers and balances via setter dependency injection:

1. The Java Model Class

package com.ram.model;

import java.util.Map;

public class Customer {
    private Map<String, String> accounts;

    // Setter method for map injection
    public void setAccounts(Map<String, String> accounts) {
        this.accounts = accounts;
    }

    public void display() {
        System.out.println("Customer Accounts:");
        for (Map.Entry<String, String> entry : accounts.entrySet()) {
            System.out.println("Account Number: " + entry.getKey() + ", Balance: " + entry.getValue());
        }
    }
}

2. Configuring applicationContext.xml

Inside the <property> element, define the entries using <map> and <entry> tags:

<bean id="customer" class="com.ram.model.Customer">
    <property name="accounts">
        <map>
            <entry key="ACC1001" value="50000" />
            <entry key="ACC1002" value="75000" />
            <entry key="ACC1003" value="120000" />
        </map>
    </property>
</bean>

3. Loading and Executing with ApplicationContext

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

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

Key Takeaway

Injecting a Map via setter dependency injection allows you to cleanly externalize key-value properties. By configuring values inside <map> and <entry> tags, Spring instantiates and populates the collection automatically before injecting it into your bean.

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How to Inject Map 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.Iterator;

import java.util.Map;

import java.util.Map.Entry;

import java.util.Set;

public class FruitShop

{

    private String shopName;

    private Map<Integer, String> mapOfAvailableFruits;

    public String getShopName()

    {

        return shopName;

    }

    public void setShopName(String shopName)

    {

        this.shopName = shopName;

    }

    public Map<Integer, String> getMapOfAvailableFruits()

    {

        return mapOfAvailableFruits;

    }

    public void setMapOfAvailableFruits(

            Map<Integer, String> mapOfAvailableFruits)

    {

        this.mapOfAvailableFruits = mapOfAvailableFruits;

    }

    public void displayFruitShopInfo()

    {

        System.out.println("FruitShop [shopName=" + shopName

                + ", mapOfAvailableFruits=" + mapOfAvailableFruits + "]");

        System.out.println("Fruit ShopName = " + shopName);

        Set<Entry<Integer, String>> set = mapOfAvailableFruits.entrySet();

        Iterator<Entry<Integer, String>> itr = set.iterator();

        while (itr.hasNext())

        {

            Entry<Integer, String> entry = itr.next();

            System.out.println("Fruit Id = " + entry.getKey()

                    + ", Fruit Name = " + entry.getValue());

        }

    }

}

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="mapOfAvailableFruits">

            <map>

                <entry key="1" value="Apple"></entry>

                <entry key="2" value="Grapes"></entry>

            </map>

        </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(Spring Container)");

        fruitShop.displayFruitShopInfo();

    }

}

Output

May 15, 2018 8:59:21 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Tue May 15 08:59:21 IST 2018]; root of context hierarchy

May 15, 2018 8:59:22 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions

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

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

Got fruitShop object from the ApplicationContext(Spring Container)

FruitShop [shopName=Fruit Mart, mapOfAvailableFruits={1=Apple, 2=Grapes}]

Fruit ShopName = Fruit Mart

Fruit Id = 1, Fruit Name = Apple

Fruit Id = 2, Fruit Name = Grapes