Spring Dependency Injection With Map Collection Example

We have already seen about how to inject dependency to a List and Set Collection, now we will look into Spring Dependency injection to a Map java collection. As we all know Map uses key, value pair to store the values. A pair of key and value is called as a entry. We will be using the <entry> tag in our configuration file to inject values.

 <property name="stringMap">
     <map>
        <entry key="1">
           <value>Welcome</value>
        </entry>
        <entry key="2">
           <value>To</value>
        </entry>
        <entry key="3">
           <value>JavaInterviewPoint</value>
        </entry>
        <entry key="4">
           <value>MapInjection</value>
        </entry>
     </map>
 </property>

Here we have configured 4 key, value pairs, the spring container which will create 4 Map.Entry class objects to hold our key value pairs. We will again take our Library and Book classes and make modifications to inject a Map.

Folder Structure:

1. Create a new Java Project  “SpringCoreTutorial” and create a package for our src files “com.javainterviewpoint“
2. Add the required libraries to the build path. Java Build Path ->Libraries ->Add External JARs and add the below jars.
   

   commons-logging-1.1.1.jar
   spring-beans-3.2.9.RELEASE.jar
   spring-core-3.2.9.RELEASE.jar
   spring-context-3.2.9.RELEASE.jar
   spring-expression-3.2.9.RELEASE.jar

3. Create the Java classes Book.java, Library.java and ClientLogic.java under  com.javainterviewpoint folder.
4. Place our configuration file SpringConfig.xml in the src directory

Book.java

Book class will have all the book details such title, author, publications and its corresponding POJO’s. 

package com.javainterviewpoint;

public class Book 
{
    private String title;
    private String author;
    private String publications;
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
    public String getAuthor() {
        return author;
    }
    public void setAuthor(String author) {
        this.author = author;
    }
    public String getPublications() {
        return publications;
    }
    public void setPublications(String publications) {
        this.publications = publications;
    }
}

Library.java

Library class has two Maps, stringMap which holds the String values and bookMap which can hold Book type of objects and its corresponding getters and setters.

package com.javainterviewpoint;

import java.util.Map;

public class Library 
{
    private Map<String,String> stringMap;
    private Map<String,Book> bookMap;
    
    public Map getStringMap() {
        return stringMap;
    }
    public void setStringMap(Map stringMap) {
        this.stringMap = stringMap;
    }
    public Map getBookMap() {
        return bookMap;
    }
    public void setBookMap(Map bookMap) {
        this.bookMap = bookMap;
    }
}

SpringConfig.xml

In our configuration file, we have defined a separate id for each bean Library and Book classes. Using the <map> tag we have set values to the properties of the Library class

<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-3.0.xsd">
 
 <bean id="library" class="com.javainterviewpoint.Library">
    <property name="bookMap">
       <map>
          <entry key="book1">
             <ref bean="book1"/>
          </entry>
          <entry key="book2">
             <ref bean="book2"/>
          </entry>
       </map>
    </property>
    <property name="stringMap">
       <map>
          <entry key="1">
             <value>Welcome</value>
          </entry>
          <entry key="2">
             <value>To</value>
          </entry>
          <entry key="3">
             <value>JavaInterviewPoint</value>
          </entry>
          <entry key="4">
             <value>MapInjection</value>
          </entry>
        </map>
      </property>
 </bean>
 <bean id="book1" class="com.javainterviewpoint.Book">
 <property name="title" value="Core Spring" />
 <property name="author" value="JavaInterviewPoint" />
 <property name="publications" value="JIP" />
 </bean>
 <bean id="book2" class="com.javainterviewpoint.Book">
 <property name="title" value="Spring MVC" />
 <property name="author" value="JavaInterviewPoint" />
 <property name="publications" value="JIP" />
 </bean>
</beans>

ClientLogic.java

package com.javainterviewpoint;

import java.util.Map;

import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.Resource;

public class ClientLogic 
{
    public static void main(String args[])
    {
        //Read the configuration file
        Resource resource = new ClassPathResource("SpringConfig.xml");
        //Read all the bean definition
        BeanFactory bf = new XmlBeanFactory(resource);
        //Get the Library Instance
        Library library = (Library)bf.getBean("library");
        //Get bookMap
        Map<String,Book> bookMap = library.getBookMap();
        //Lets print the properties of the Book
        int flag=1;
        for(Map.Entry<String,Book> entry : bookMap.entrySet())
        {
            Book book = (Book)entry.getValue();
            System.out.println("**Book"+flag+" Properties**");
            System.out.println("Book Title        : "+book.getTitle());
            System.out.println("Book Author       : "+book.getAuthor());
            System.out.println("Book Publications : "+book.getPublications());
            flag++;
        }
        //Lets print the primitives
        Map stringMap = library.getStringMap();
        System.out.println("Primitives set to Map : "+stringMap);
    }
}

• Resource class reads our Configuration File(SpringConfig.xml)
• BeanFactory class read all the bean definition mentioned in the config file.
• Get the Library Class instance by calling the getBean() method over the bean factory.
• As we have already injected values to both of the Map of the Library class through our Config file. We will call the corresponding getters to get the values associated with it.

Output

On running the ClientLogic.java we will get the below output

**Book1 Properties**
Book Title        : Core Spring
Book Author       : JavaInterviewPoint
Book Publications : JIP
**Book2 Properties**
Book Title        : Spring MVC
Book Author       : JavaInterviewPoint
Book Publications : JIP
Primitives set to Map : {1=Welcome, 2=To, 3=JavaInterviewPoint, 4=MapInjection}