JAVA EE: Spring Expression Language – Accessing List Collection [Annotation]

Thursday, 25 October 2018

Spring Expression Language – Accessing List Collection [Annotation] | Spring Tutorial

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Overview: Accessing List Elements in SpEL

The Spring Expression Language (SpEL) offers built-in support for manipulating collections, including java.util.List structures. When developing applications using annotation-based configuration, you can retrieve individual items from a list directly by index without writing procedural extraction code.

In this guide, you will learn how to access specific elements of a List collection using zero-based indexing along with the @Value annotation.

Understanding SpEL List Indexing Syntax

SpEL uses intuitive square bracket notation [index] to access items in an indexed collection:

Zero-Based Index: The first element in the collection is referenced at index 0, the second at 1, and so on: @Value("#{beanName.listProperty[0]}").
Automatic Type Casting: Spring handles the type resolution and casts the extracted element into your target field's declared type automatically.
Property Chaining: You can chain further properties or method calls directly onto the accessed element, e.g., @Value("#{beanName.listProperty[0].name}").

Step-by-Step Configuration

Define the Source Bean: Create a Spring-managed bean containing a populated List of elements (such as city names, integers, or domain models).
Apply @Value: In your target component, annotate your field using bracket indexing, e.g., @Value("#{cityBean.cityList[1]}").
Verify Injection: Load the application context to verify that Spring extracts and injects the specified list item properly.

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Spring Expression Language – Accessing List Collection [Annotation] | 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>5.0.5.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>

AddressInfo.java

package com.ram.model;

import java.util.ArrayList;

import java.util.List;

import org.springframework.stereotype.Component;

@Component("addressInfo")

public class AddressInfo

{

    private List<String> addressList;

    public AddressInfo()

    {

        addressList = new ArrayList<String>();

        addressList.add("B220, East Street, London");

        addressList.add("A220, West Street, London");

        addressList.add("C220, North Street, London");

    }

    public List<String> getAddressList()

    {

        return addressList;

    }

    public void setAddressList(List<String> addressList)

    {

        this.addressList = addressList;

    }

    @Override

    public String toString()

    {

        return "AddressInfo [addressList=" + addressList + "]";

    }

}

Employee.java

package com.ram.model;

import org.springframework.beans.factory.annotation.Value;

import org.springframework.stereotype.Component;

@Component("employee")

public class Employee

{

    @Value("10")

    private int id;

    @Value("Peter")

    private String name;

    @Value("#{addressInfo.addressList[0]}")

    private String firstAddress;

    @Value("#{addressInfo.addressList[1]}")

    private String secondAddress;

    public int getId()

    {

        return id;

    }

    public void setId(int id)

    {

        this.id = id;

    }

    public String getName()

    {

        return name;

    }

    public void setName(String name)

    {

        this.name = name;

    }

    public String getFirstAddress()

    {

        return firstAddress;

    }

    public void setFirstAddress(String firstAddress)

    {

        this.firstAddress = firstAddress;

    }

    public String getSecondAddress()

    {

        return secondAddress;

    }

    public void setSecondAddress(String secondAddress)

    {

        this.secondAddress = secondAddress;

    }

    @Override

    public String toString()

    {

        return "Employee [id=" + id + ", name=" + name + ", firstAddress="

                + firstAddress + ", secondAddress=" + secondAddress + "]";

    }

}

applicationContext.xml

<beans xmlns="http://www.springframework.org/schema/beans"

    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 

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

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

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

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

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

    <context:component-scan base-package="com.ram" />

</beans>

App.java

package com.ram.core;

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.ram.model.Employee;

import com.ram.model.AddressInfo;

public class App

{

    public static void main(String[] args)

    {

        ApplicationContext context = new ClassPathXmlApplicationContext(

                "applicationContext.xml");

        System.out.println("---------------------------------------");

        AddressInfo addressInfo = (AddressInfo) context

                .getBean("addressInfo");

        System.out.println(addressInfo+"\n");

        Employee employee = (Employee) context.getBean("employee");

        System.out.println(employee);

    }

}

Output

Sep 15, 2018 10:01:11 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@736e9adb: startup date [Sat Sep 15 10:01:11 IST 2018]; root of context hierarchy

Sep 15, 2018 10:01:11 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions

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

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

AddressInfo [addressList=[B220, East Street, London, A220, West Street, London, C220, North Street, London]]

Employee [id=10, name=Peter, firstAddress=B220, East Street, London, secondAddress=A220, West Street, London]