JAVA EE: Spring Util Schema

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Friday, 10 August 2018

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

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Overview: Concrete Map Collections with util:map in Spring

In the Spring Framework, managing collections inside XML configuration can sometimes become verbose when using standard bean definitions. The Spring util schema offers concise, dedicated XML tags to declare collection beans directly. With the <util:map> element, you can easily instantiate concrete map implementations such as java.util.HashMap or java.util.TreeMap as standalone beans.

In this guide, you will learn how to declare concrete Map collection beans using the util:map namespace, configure their implementation classes, and inject them cleanly into your Spring beans.

Why Use <util:map> in Spring?

The util:map tag simplifies collection bean configuration with several benefits:

Clean & Concise XML: Eliminates boilerplate MapFactoryBean declarations by providing a dedicated, expressive schema element.
Concrete Class Customization: Use the map-class attribute to specify concrete collection types such as java.util.HashMap, java.util.LinkedHashMap, or java.util.TreeMap.
Standalone Reusable Bean: Defines a map bean with its own id, allowing it to be shared and injected across multiple collaborating beans.
Sorting & Ordering: Specifying java.util.TreeMap guarantees that keys are kept in their natural sorted order.

Step-by-Step Configuration

Declare the Util Namespace: Add the util schema definition to your Spring XML configuration:
xmlns:util="http://www.springframework.org/schema/util"
Define the Map with util:map: Set the desired concrete class via map-class and add key-value entries:
<util:map id="countryCapitals" map-class="java.util.TreeMap"> <entry key="India" value="New Delhi"/> <entry key="USA" value="Washington D.C."/> </util:map>
Inject the Map into Target Bean: Reference the map bean in your target bean definition:
<bean id="countryService" class="com.example.CountryService"> <property name="capitals" ref="countryCapitals"/> </bean>

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How to create a concrete Map collection class (HashMap and TreeMap) using util:map 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">

            <util:map map-class="java.util.HashMap">

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

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

            </util: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

Jul 30, 2018 9:46:08 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Mon Jul 30 09:46:08 IST 2018]; root of context hierarchy

Jul 30, 2018 9:46:08 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