Spring DI - Injecting Collections 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 pke 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 <pst> 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

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 apppcation to run and test.

Here is the content of JavaCollection.java file −

package com.tutorialspoint;
import java.util.*;

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

   pubpc JavaCollection() {}

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

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

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

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

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

Following is the content of the MainApp.java file −

package com.tutorialspoint;

import org.springframework.context.ApppcationContext;
import org.springframework.context.support.ClassPathXmlApppcationContext;

pubpc class MainApp {
   pubpc static void main(String[] args) {
      ApppcationContext context = new ClassPathXmlApppcationContext("apppcationcontext.xml");
      JavaCollection jc=(JavaCollection)context.getBean("javaCollection");

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

Following is the configuration file apppcationcontext.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">
         <pst>
            <value>INDIA</value>
            <value>JAPAN</value>
            <value>USA</value>
            <value>UK</value>
         </pst>
      </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>

Once you are done creating the source and bean configuration files, let us run the apppcation. If everything is fine with your apppcation, 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}