Spring Dependency Injection With List Collection Example

In my previous article we have already learnt about the Dependency Injection in Spring and Setter Injection in the form of Primitives and injection in the form of Objects. Spring support injection in the form of the collection as well, it supports the below collections.

1. List
2. Set
3. Map
4. Properties

Lets take it one by one in this tutorial we will learn how to inject values to the List Collection. We will be injecting String values to a list and Objects to another list using <list> tag in our configuration file.

 <property name="stringList">
     <list>
         <value>Welcome</value>
         <value>To</value>
         <value>JavaInterivewPoint</value>
     </list>
 </property>            

When our client calls the Library class bean id “library“, the below happens which is not actually visible

List<String> list = new ArrayList<String>();
list.add("Welcome");
list.add("To");
list.add("JavaInterviewPoint");

lets see the complete example.

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 Lists, stringList which holds the String values and bookList which can hold Book type of objects and its corresponding getters and setters.

package com.javainterviewpoint;

import java.util.List;

public class Library 
{
    private List stringList;
    private List bookList;
    
    public List getStringList() {
        return stringList;
    }
    public void setStringList(List stringList) {
        this.stringList = stringList;
    }
    public List getBookList() {
        return bookList;
    }
    public void setBookList(List bookList) {
        this.bookList = bookList;
    }
}

SpringConfig.xml

In our configuration file we have defined seperate id for each bean Library and Book classes. Using the <list> 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="bookList">
             <list>
                <ref bean="book1"/>
                <ref bean="book2"/>
             </list>
         </property>
         <property name="stringList">
             <list>
                 <value>Welcome</value>
                 <value>To</value>
                 <value>JavaInterivewPoint</value>
              </list>
         </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.List;

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");
        //List of Books
        List bookList = library.getBookList();
        //Lets print the properties of the Book
        for(int i=0;i<bookList.size();i++)
        {
            System.out.println("**Book"+(i+1)+" Properties**");
            Book book = bookList.get(i);
            System.out.println("Book Title        : "+book.getTitle());
            System.out.println("Book Author       : "+book.getAuthor());
            System.out.println("Book Publications : "+book.getPublications());
        }
        //Lets print the primitives
        List stringList = library.getStringList();
        System.out.println("Primitives set to List : "+stringList);
    }
}

• 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 List of the Library class through our Config file. We will call the corresponding Lists getter 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 List : [Welcome, To, JavaInterivewPoint]