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

Friday, 1 June 2018

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

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Introduction

In Spring applications, you often need to pass key-value collections to configure components. Spring's IoC container provides built-in support for mapping key-value pairs directly into a java.util.Map using constructor dependency injection.

In this tutorial, you will learn how to configure and inject a basic Map with String keys and values into a Java class via its constructor.

1. Create the Java Bean Class

Create a model or service class (such as FruitShop) that accepts a Map<String, String> inside its constructor:

import java.util.Map;

public class FruitShop {
    private String shopName;
    private Map<String, String> fruitsMap;

    public FruitShop(String shopName, Map<String, String> fruitsMap) {
        this.shopName = shopName;
        this.fruitsMap = fruitsMap;
    }

    public void displayFruitShopInfo() {
        System.out.println("Shop Name: " + shopName);
        System.out.println("Fruits Inventory:");
        for (Map.Entry<String, String> entry : fruitsMap.entrySet()) {
            System.out.println("Code: " + entry.getKey() + " -> Name: " + entry.getValue());
        }
    }
}

2. Configure Spring XML with <map> and <entry>

In your applicationContext.xml, configure the bean using the <constructor-arg> element along with the <map> and <entry> sub-elements:

<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="fruitShop" class="FruitShop">
        <constructor-arg value="City Fresh Supermarket" />
        <constructor-arg>
            <map>
                <entry key="F101" value="Apple" />
                <entry key="F102" value="Orange" />
                <entry key="F103" value="Banana" />
            </map>
        </constructor-arg>
    </bean>

</beans>

3. Load Context and Run the Application

Use ClassPathXmlApplicationContext to bootstrap the Spring IoC container, retrieve the configured bean, and execute 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");
        FruitShop shop = (FruitShop) context.getBean("fruitShop");
        shop.displayFruitShopInfo();
    }
}

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How to Inject Map 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>

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 FruitShop(String shopName, Map<Integer, String> mapOfAvailableFruits)

    {

        System.out.println(

                "FruitShop(String shopName, Map<Integer, String> mapOfAvailableFruits) "

                        + "constructor is called by the Spring container");

        this.shopName = shopName;

        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">

        <constructor-arg type="String" value="Fruit Mart"></constructor-arg>

        <constructor-arg type="java.util.Map">

            <map>

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

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

            </map>

        </constructor-arg>

    </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

Apr 28, 2018 9:16:50 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Sat Apr 28 09:16:50 IST 2018]; root of context hierarchy

Apr 28, 2018 9:16:51 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions

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

FruitShop(String shopName, Map<Integer, String> mapOfAvailableFruits) constructor is called by the Spring container

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

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