JAVA EE: Spring Expression Language – Accessing Map[Annotation]

Thursday, 25 October 2018

Spring Expression Language – Accessing Map[Annotation] | Spring Tutorial

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Overview: Accessing Maps in SpEL Using Annotations

The Spring Expression Language (SpEL) offers native support for querying Java collections, including Map data structures. When configuring your components with modern Spring annotations, you can extract values from a map directly into target fields without manual lookups or helper utility methods.

In this guide, you will learn how to access map entries using indexer notation along with the @Value annotation in an annotation-driven Spring configuration.

Understanding SpEL Map Syntax

SpEL provides an intuitive bracket notation to access map values by key:

Bracket Key Notation: Query any key using brackets and quotes: @Value("#{beanName.mapProperty['targetKey']}").
Dot Notation: If the key is an alphanumeric string without special characters, SpEL also allows dot notation: @Value("#{beanName.mapProperty.targetKey}").
Dynamic Injection: The Spring container evaluates the expression during bean post-processing and injects the retrieved value automatically.

Step-by-Step Configuration

Create the Source Bean: Define a Spring bean containing an initialized Map<String, String> or Map<String, Object>.
Apply @Value: In your consumer component, annotate a property using the SpEL map reference: @Value("#{telephoneBean.telephoneMap['US']}").
Initialize Application Context: Run your Spring context to observe the automatic extraction and injection of the map's corresponding value.

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Spring Expression Language – Accessing Map[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.LinkedHashMap;

import java.util.Map;

import org.springframework.stereotype.Component;

@Component("addressInfo")

public class AddressInfo

{

    private Map<Integer, String> addressMap;

    public AddressInfo()

    {

        addressMap = new LinkedHashMap<Integer, String>();

        addressMap.put(1, "B220-East Street-London");

        addressMap.put(2, "A220-West Street-London");

        addressMap.put(3, "C220-North Street-London");

    }

    public Map<Integer, String> getAddressMap()

    {

        return addressMap;

    }

    public void setAddressMap(Map<Integer, String> addressMap)

    {

        this.addressMap = addressMap;

    }

    @Override

    public String toString()

    {

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

    }

}

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.addressMap[1]}")

    private String firstAddress;

    @Value("#{addressInfo.addressMap[2]}")

    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 17, 2018 9:42:51 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@736e9adb: startup date [Mon Sep 17 09:42:51 IST 2018]; root of context hierarchy

Sep 17, 2018 9:42:51 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions

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

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

AddressInfo [addressMap={1=B220-East Street-London, 2=A220-West Street-London, 3=C220-North Street-London}]

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