JAVA EE: MapFactoryBean

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Friday, 10 August 2018

How to create a concrete Map collection class (HashMap and TreeMap) using mapFactoryBean in Spring

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Overview: Configuring Concrete Maps with MapFactoryBean

In the Spring Framework, injecting collections such as Map is a common task. By default, Spring instantiates standard map implementations when using built-in XML collection tags. However, when your application requires a specific concrete collection class—such as a HashMap, sorted TreeMap, or concurrent map—Spring's MapFactoryBean provides precise control over the exact map type instantiated and populated in the container.

In this guide, you will learn how to configure MapFactoryBean to create concrete Map collections like HashMap and TreeMap, populate them with key-value pairs, and inject them into your Spring beans.

Understanding MapFactoryBean

MapFactoryBean is a built-in Spring helper class that creates concrete map instances with customized behavior:

Target Concrete Class: Allows you to define the exact implementation class via the targetMapClass property (e.g., java.util.HashMap or java.util.TreeMap).
Pre-Populated Key-Value Pairs: Accepts source map entries through its sourceMap property and copies them into the newly instantiated target map.
Sorted and Ordered Maps: When configuring a TreeMap, keys are automatically maintained in natural sorted order, making it ideal for ordered lookups.
Reusable Map Beans: Produces a standalone bean that can be injected into multiple collaborator beans across your Spring context.

Step-by-Step Implementation

Declare MapFactoryBean in XML: Configure the bean using org.springframework.beans.factory.config.MapFactoryBean.
Specify the Target Map Class: Set targetMapClass to your chosen map implementation:
<property name="targetMapClass" value="java.util.TreeMap"/>
Populate Source Map Entries: Add key-value entries inside the sourceMap property:
<property name="sourceMap"> <map> <entry key="India" value="New Delhi"/> <entry key="USA" value="Washington D.C."/> </map> </property>
Inject into Target Bean: Reference the created map bean in your dependent class using the standard ref attribute.

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How to create a concrete Map collection class (HashMap and TreeMap) using mapFactoryBean in Spring

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" 

    xmlns:util="http://www.springframework.org/schema/util"

    xsi:schemaLocation="http://www.springframework.org/schema/beans

    http://www.springframework.org/schema/beans/spring-beans-4.3.xsd

    http://www.springframework.org/schema/util

    http://www.springframework.org/schema/util/spring-util-4.3.xsd">

    <bean id="fruitShop" class="com.ram.core.FruitShop">

        <property name="shopName" value="Fruit Mart"></property>

        <property name="mapOfAvailableFruits">

            <bean class="org.springframework.beans.factory.config.MapFactoryBean">

                <property name="targetMapClass">

                    <value>java.util.HashMap</value>

                </property>

                <property name="sourceMap">

                    <map>

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

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

                    </map>

                </property>             

            </bean>

        </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

Jul 31, 2018 9:22:25 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Tue Jul 31 09:22:25 IST 2018]; root of context hierarchy

Jul 31, 2018 9:22:25 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