JAVA EE: How to create a concrete List collection class (ArrayList and LinkedList) using util:list in Spring

Tuesday, 7 August 2018

How to create a concrete List collection class (ArrayList and LinkedList) using util:list in Spring

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Introduction

In the Spring Framework, defining collections directly using the util schema is concise, modern, and readable. Using the util:list element, you can easily instantiate and inject concrete List implementations such as java.util.ArrayList or java.util.LinkedList as first-class, standalone Spring beans.

Why Use util:list?

Explicit Concrete Implementation: Use the list-class attribute to specify whether your bean is an ArrayList or a LinkedList.
Clean and Concise XML: Eliminates verbose factory bean declarations while remaining fully declarative.
Standalone Reusability: Create standalone collection beans that can be referenced across multiple bean definitions via ref.

Step-by-Step Configuration

First, ensure the Spring util namespace is defined at the top of your XML context configuration:

xmlns:util="http://www.springframework.org/schema/util"
xsi:schemaLocation="... http://www.springframework.org/schema/util 
http://www.springframework.org/schema/util/spring-util.xsd"

1. Defining an ArrayList with util:list

<util:list id="cityArrayList" list-class="java.util.ArrayList">
    <value>New York</value>
    <value>London</value>
    <value>Tokyo</value>
</util:list>

2. Defining a LinkedList with util:list

<util:list id="cityLinkedList" list-class="java.util.LinkedList">
    <value>New York</value>
    <value>London</value>
    <value>Tokyo</value>
</util:list>

Key Takeaway

The util:list tag offers a cleaner syntax than traditional factory beans. If your application needs rapid index-based lookups, configure ArrayList; for frequent element insertions or deletions, switch to LinkedList seamlessly via the list-class attribute.

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How to create a concrete List collection class (ArrayList and LinkedList) using util:list 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.List;

public class FruitShop

{

    private String shopName;

    private List<String> listOfAvailableFruits;

    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 List<String> getListOfAvailableFruits()

    {

        return listOfAvailableFruits;

    }

    public void setListOfAvailableFruits(List<String> listOfAvailableFruits)

    {

        System.out.println(

                "setListOfAvailableFruits(List<String> listOfAvailableFruits) is "

                        + "called by the Spring Container");

        this.listOfAvailableFruits = listOfAvailableFruits;

    }

    public void displayFruitShopInfo()

    {

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

                + ", listOfAvailableFruits=" + listOfAvailableFruits + "]");

    }

}

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="listOfAvailableFruits">

            <util:list list-class="java.util.LinkedList">

                <value>apple</value>

                <value>pineapple</value>

                <value>orange</value>

            </util:list>

        </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 28, 2018 11:41:03 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Sat Jul 28 11:41:03 IST 2018]; root of context hierarchy

Jul 28, 2018 11:41:04 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

setListOfAvailableFruits(List<String> listOfAvailableFruits) is called by the Spring Container

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

Got fruitShop object from the ApplicationContext(Spring Container)

FruitShop [shopName=Fruit Mart, listOfAvailableFruits=[apple, pineapple, orange]]