Spring DI - Injecting Map Reference via Constructor

You have seen how to configure primitive data type using value attribute and object references using ref attribute of the <property> tag in your Bean configuration file. Both the cases deal with passing singular value to a bean.

Now what if you want to pass Map. In this example, we're showcasing passing direct values of the Map using constructor injection.

Example - Usage of Constructor Based DI of Map Refs

Let's update the project created in Spring DI - Create Project chapter. We're adding following files −

• Address.java − A class to be used as dependency.

• JavaCollection.java − A class containing a collections of dependencies.

• MainApp.java − Main application to run and test.

Address.java

Here is the content of Address.java file −

package com.tutorialspoint;

public class Address {
   private String name;

   public String getName() {
      return name;
   }
   public void setName(String name) {
      this.name = name;
   }	
   @Override
   public String toString() {
      return name;
   }
}

JavaCollection.java

Here is the content of JavaCollection.java file −

package com.tutorialspoint;

import java.util.Map;

public class JavaCollection {
   Map<String, Address>  addressMap;
   public JavaCollection() {}

   public JavaCollection(Map<String, Address> addressMap) {
      this.addressMap = addressMap;
   }

   // a setter method to set Map
   public void setAddressMap(Map<String, Address> addressMap) {
      this.addressMap = addressMap;
   }

   // prints and returns all the elements of the Map.
   public Map<String, Address> getAddressMap() {
      System.out.println("Map Elements :"  + addressMap);
      return addressMap;
   }
}

MainApp.java

Following is the content of the MainApp.java file −

package com.tutorialspoint;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainApp {
   public static void main(String[] args) {
      ApplicationContext context = new ClassPathXmlApplicationContext("applicationcontext.xml");
      JavaCollection jc=(JavaCollection)context.getBean("javaCollection");
      jc.getAddressMap();
   }
}

applicationcontext.xml

Following is the configuration file applicationcontext.xml which has configuration for all the type of collections −

<?xml version = "1.0" encoding = "UTF-8"?>

<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 = "address1" class = "com.tutorialspoint.Address">
      <property name="name" value="INDIA"></property>
   </bean>
   <bean id = "address2" class = "com.tutorialspoint.Address">
      <property name="name" value="JAPAN"></property>
   </bean>
   <bean id = "address3" class = "com.tutorialspoint.Address">
      <property name="name" value="USA"></property>
   </bean>
   <bean id = "address4" class = "com.tutorialspoint.Address">
      <property name="name" value="UK"></property>
   </bean>
   <bean id = "javaCollection" class = "com.tutorialspoint.JavaCollection">
      <constructor-arg name = "addressMap">
         <map>
            <entry key = "1" value-ref = "address1"/>
            <entry key = "2" value-ref = "address2"/>
            <entry key = "3" value-ref = "address3"/>
            <entry key = "4" value-ref = "address4"/>
         </map>
      </constructor-arg>
   </bean>
</beans>

Output

Once you are done creating the source and bean configuration files, let us run the application. If everything is fine with your application, it will print the following message −

Map Elements :{1=INDIA, 2=JAPAN, 3=USA, 4=UK}