JAVA EE: June 2018

Friday, 29 June 2018

How to Inject Map having Dependent Object in key and value using DI by Setter method

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Introduction

In Spring Framework, configuring collection dependencies often involves key-value mappings where both the keys and values are custom bean references rather than primitive types. Spring provides robust XML configuration tags like <map> and <entry> with attributes such as key-ref and value-ref to inject complex java.util.Map structures using setter-based dependency injection.

Why Inject Dependent Objects in Map Keys and Values?

Complex Domain Associations: Allows mapping distinct entity objects (e.g., a Department key to an Employee value) directly through configuration.
key-ref & value-ref Attributes: Eliminates boilerplate lookup code by wiring independent Spring bean definitions into map entries seamlessly.
Decoupled Architecture: Keeps configuration of individual collaborators modular and easily reusable across other beans in the application context.

Step-by-Step Code Example

Here is an example showing how to configure and inject a Map where both key and value are dependent collaborator objects:

1. The Model Classes

package com.ram.model;

import java.util.Map;

// Key Object
public class Department {
    private String deptName;

    public void setDeptName(String deptName) {
        this.deptName = deptName;
    }

    @Override
    public String toString() {
        return "Department [deptName=" + deptName + "]";
    }
}

// Value Object
public class Employee {
    private String empName;

    public void setEmpName(String empName) {
        this.empName = empName;
    }

    @Override
    public String toString() {
        return "Employee [empName=" + empName + "]";
    }
}

// Consumer Class holding the Map
public class Organization {
    private Map<Department, Employee> deptHeadMap;

    // Setter method for map injection
    public void setDeptHeadMap(Map<Department, Employee> deptHeadMap) {
        this.deptHeadMap = deptHeadMap;
    }

    public void display() {
        for (Map.Entry<Department, Employee> entry : deptHeadMap.entrySet()) {
            System.out.println(entry.getKey() + " -> " + entry.getValue());
        }
    }
}

2. Configuring applicationContext.xml

Use key-ref and value-ref inside the <entry> element to reference existing bean definitions:

<!-- Dependent Bean Definitions -->
<bean id="deptIT" class="com.ram.model.Department">
    <property name="deptName" value="Information Technology" />
</bean>

<bean id="empRam" class="com.ram.model.Employee">
    <property name="empName" value="Ram" />
</bean>

<!-- Organization Bean with Map Setter Injection -->
<bean id="organization" class="com.ram.model.Organization">
    <property name="deptHeadMap">
        <map>
            <entry key-ref="deptIT" value-ref="empRam" />
        </map>
    </property>
</bean>

3. Loading and Executing the Application

ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");

Organization org = (Organization) context.getBean("organization");
org.display();

Key Takeaway

Spring makes wiring complex data structures easy through <entry key-ref="..." value-ref="..."/>. This allows full decoupling of key and value object configurations while letting Spring's IoC container inject complete, ready-to-use maps into your beans.

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How to Inject Map having Dependent Object in key and value using DI by Setter method

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>

Fruit.java

package com.ram.model;

public class Fruit

{

    private String name;

    private String color;

    public String getName()

    {

        return name;

    }

    public void setName(String name)

    {

        this.name = name;

    }

    public String getColor()

    {

        return color;

    }

    public void setColor(String color)

    {

        this.color = color;

    }

    @Override

    public String toString()

    {

        return "Fruit [name=" + name + ", color=" + color + "]";

    }

}

FruitSeller.java

package com.ram.model;

public class FruitSeller

{

    private String name;

    private String emailId;

    public String getName()

    {

        return name;

    }

    public void setName(String name)

    {

        this.name = name;

    }

    public String getEmailId()

    {

        return emailId;

    }

    public void setEmailId(String emailId)

    {

        this.emailId = emailId;

    }

    @Override

    public String toString()

    {

        return "FruitSeller [name=" + name + ", emailId=" + emailId + "]";

    }

}

FruitInfo.java

package com.ram.core;

import java.util.Iterator;

import java.util.Map;

import java.util.Map.Entry;

import java.util.Set;

import com.ram.model.Fruit;

import com.ram.model.FruitSeller;

public class FruitInfo

{

    private Map<FruitSeller, Fruit> mapOfFruitSellerAndFruit;

    public Map<FruitSeller, Fruit> getMapOfFruitSellerAndFruit()

    {

        return mapOfFruitSellerAndFruit;

    }

    public void setMapOfFruitSellerAndFruit(

            Map<FruitSeller, Fruit> mapOfFruitSellerAndFruit)

    {

        this.mapOfFruitSellerAndFruit = mapOfFruitSellerAndFruit;

    }

    public void displayFruitInfo()

    {

        System.out.println("FruitInfo [mapOfFruitSellerAndFruit="

                + mapOfFruitSellerAndFruit + "]");

        Set<Entry<FruitSeller, Fruit>> set = mapOfFruitSellerAndFruit

                .entrySet();

        Iterator<Entry<FruitSeller, Fruit>> itr = set.iterator();

        while (itr.hasNext())

        {

            Entry<FruitSeller, Fruit> entry = itr.next();

            System.out.println("FruitSeller = " + entry.getKey() + ", Fruit = "

                    + entry.getValue());

        }

    }

}

applicationContext.xml

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

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

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

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

    <bean id="fruitSeller1" class="com.ram.model.FruitSeller">

        <property name="name" value="Peter"></property>

        <property name="emailId" value="Peter@yahoo.com"></property>

    </bean>

    <bean id="fruitSeller2" class="com.ram.model.FruitSeller">

        <property name="name" value="John"></property>

        <property name="emailId" value="John@gmail.com"></property>

    </bean>

    <bean id="fruit1" class="com.ram.model.Fruit">

        <property name="name" value="Apple"></property>

        <property name="color" value="Red"></property>

    </bean>

    <bean id="fruit2" class="com.ram.model.Fruit">

        <property name="name" value="Grapes"></property>

        <property name="color" value="Violet"></property>

    </bean>

    <bean id="fruitInfo" class="com.ram.core.FruitInfo">

        <property name="mapOfFruitSellerAndFruit">

            <map>

                <entry key-ref="fruitSeller1" value-ref="fruit1"></entry>

                <entry key-ref="fruitSeller2" value-ref="fruit2"></entry>

            </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("---------------------------------------");

        FruitInfo fruitInfo = (FruitInfo) context.getBean("fruitInfo");

        System.out.println(

                "Got fruitInfo object from the ApplicationContext(Spring container)");

        fruitInfo.displayFruitInfo();

    }

}

Output

May 17, 2018 8:47:52 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Thu May 17 08:47:52 IST 2018]; root of context hierarchy

May 17, 2018 8:47:52 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions

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

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

Got fruitInfo object from the ApplicationContext(Spring container)

FruitInfo [mapOfFruitSellerAndFruit={FruitSeller [name=Peter, emailId=Peter@yahoo.com]=Fruit [name=Apple, color=Red], FruitSeller [name=John, emailId=John@gmail.com]=Fruit [name=Grapes, color=Violet]}]

FruitSeller = FruitSeller [name=Peter, emailId=Peter@yahoo.com], Fruit = Fruit [name=Apple, color=Red]

FruitSeller = FruitSeller [name=John, emailId=John@gmail.com], Fruit = Fruit [name=Grapes, color=Violet]

Click the below link to download the code:
https://sites.google.com/site/ramj2eev2/java_basics/SpringDemo_Setter_DI_Map_KVDependentObject.zip?attredirects=0&d=1

Github Link:
https://github.com/ramram43210/javaee/tree/master/Spring_2018/SpringDemo_Setter_DI_Map_KVDependentObject

Bitbucket Link:
https://bitbucket.org/ramram43210/spring/src/00d9c316f5df8a9bcb6603e70c0baf4d24d6fdcd/Spring_2018/SpringDemo_Setter_DI_Map_KVDependentObject/?at=master

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How to Inject Map having Dependent Object in value using dependency injection by Setter method?

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Introduction

In Spring Framework applications, configuring a java.util.Map where the key is a simple literal (such as a String) and the value is a custom dependent object bean reference is a very common scenario. Spring makes this simple and expressive in XML using the <map> and <entry> tags along with the key and value-ref attributes via setter-based dependency injection.

Why Inject Dependent Objects in Map Values?

Key-Based Bean Lookup: Allows mapping straightforward string keys (like department codes or role titles) directly to complex collaborator beans.
value-ref Attribute: Seamlessly wires independent Spring bean definitions as map values without writing custom population code.
Clean Separation: Allows collaborator beans to be declared independently and injected into maps across multiple beans cleanly.

Step-by-Step Code Example

Here is an example showing how to inject a Map<String, Employee> where the value is a dependent Employee bean:

1. The Model Classes

package com.ram.model;

import java.util.Map;

// Dependent Object (Value)
public class Employee {
    private String name;
    private String role;

    public void setName(String name) {
        this.name = name;
    }

    public void setRole(String role) {
        this.role = role;
    }

    @Override
    public String toString() {
        return "Employee [name=" + name + ", role=" + role + "]";
    }
}

// Consumer Class holding the Map
public class Organization {
    private Map<String, Employee> employeesMap;

    // Setter method for dependency injection
    public void setEmployeesMap(Map<String, Employee> employeesMap) {
        this.employeesMap = employeesMap;
    }

    public void display() {
        for (Map.Entry<String, Employee> entry : employeesMap.entrySet()) {
            System.out.println("Key: " + entry.getKey() + " -> " + entry.getValue());
        }
    }
}

2. Configuring applicationContext.xml

Use key for the string identifier and value-ref to point to the dependent bean definition:

<!-- Dependent Bean Definitions -->
<bean id="emp1" class="com.ram.model.Employee">
    <property name="name" value="Ram" />
    <property name="role" value="Technical Lead" />
</bean>

<bean id="emp2" class="com.ram.model.Employee">
    <property name="name" value="Peter" />
    <property name="role" value="Developer" />
</bean>

<!-- Organization Bean with Map Setter Injection -->
<bean id="organization" class="com.ram.model.Organization">
    <property name="employeesMap">
        <map>
            <entry key="LEAD" value-ref="emp1" />
            <entry key="DEV" value-ref="emp2" />
        </map>
    </property>
</bean>

3. Loading and Executing with ApplicationContext

ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");

Organization org = (Organization) context.getBean("organization");
org.display();