Spring DI - Injecting Collections 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 plural values like Java Collection types such as List, Set, and Properties. To handle the situation, Spring offers following types of collection configuration elements which are as follows −

You can use either <list> or <set> to wire any implementation of java.util.Collection or an array.

In this example, we're showcasing passing direct values of the collection elements.

Example - Usage of Constructor Based DI of Collections

The following example shows a class JavaCollection that is using collections as dependency injected using constructor arguments.

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

• JavaCollection.java − A class containing a collections as dependency.

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

JavaCollection.java

Here is the content of JavaCollection.java file −

package com.tutorialspoint;

import java.util.List;
import java.util.Properties;
import java.util.Set;

public class JavaCollection {
   List<String> addressList;
   Set<String>  addressSet;
   Properties addressProp;

   public JavaCollection() {}

   public JavaCollection(List<String> addressList, Set<String> addressSet, 
      Properties addressProp) {
      this.addressList = addressList;
      this.addressSet = addressSet;
      this.addressProp = addressProp;
   }
   // a setter method to set List
   public void setAddressList(List<String> addressList) {
      this.addressList = addressList;
   }
   
   // prints and returns all the elements of the list.
   public List<String> getAddressList() {
      System.out.println("List Elements :"  + addressList);
      return addressList;
   }

   // a setter method to set Set
   public void setAddressSet(Set<String> addressSet) {
      this.addressSet = addressSet;
   }

   // prints and returns all the elements of the Set.
   public Set<String> getAddressSet() {
      System.out.println("Set Elements :"  + addressSet);
      return addressSet;
   }

   // a setter method to set Property
   public void setAddressProp(Properties addressProp) {
      this.addressProp = addressProp;
   }

   // prints and returns all the elements of the Property.
   public Properties getAddressProp() {
      System.out.println("Property Elements :"  + addressProp);
      return addressProp;
   }
}

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.getAddressList();
      jc.getAddressSet();
      jc.getAddressProp();
   }
}

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 = "javaCollection" class = "com.tutorialspoint.JavaCollection">
      <constructor-arg name = "addressList">
         <list>
            <value>INDIA</value>
            <value>JAPAN</value>
            <value>USA</value>
            <value>UK</value>
         </list>
      </constructor-arg>
      <constructor-arg name = "addressSet">
         <set>
            <value>INDIA</value>
            <value>JAPAN</value>
            <value>USA</value>
            <value>UK</value>
         </set>
      </constructor-arg>
      <constructor-arg name = "addressProp">
         <props>
            <prop key = "one">INDIA</prop>
            <prop key = "two">JAPAN</prop>
            <prop key = "three">USA</prop>
            <prop key = "four">UK</prop>
         </props>
      </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 −

List Elements :[INDIA, JAPAN, USA, UK]
Set Elements :[INDIA, JAPAN, USA, UK]
Property Elements :{four=UK, one=INDIA, two=JAPAN, three=USA}