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In this tutorial, we will explain how to configure a collection of objects with Spring Framework. A collection of object could be stored in an array or Java collections such as - List, Set, Map. Let's begin with configuring a collection of objects stored within a Java List.

We are going to explain how to configure a collection of objects stored within a List collection using the <list> tag of Spring Framework within its configuration XML file.

Creating the Java class - Company

We are going to create a java class named Company within the decodejava package and this class contains a String property named name and a List collection to contain objects of Employee class. Besides this, we are also going to define a couple of getter and setter methods within this class to set the List collection and the String property.

package decodejava;

import java.util.List;

public class Company 
{
 public String name;
 public List<Employee> employees;
 
 
public String getName() 
{
	return name;
}


public void setName(String name) 
{
	this.name = name;
}


public List<Employee> getEmployees()
{
	return employees;
}


public void setEmployees(List<Employee> employees)
{
	this.employees = employees;
}

}

Creating a Java Class - Employee

Next, we are going to add another Java class named Employee and it is going to contain a String property and a primitive int property.

The properties will be assigned a value by the Spring Container, when the Employee bean is created by it using the configuration xml file(to be created in the upcoming section).

package decodejava;

public class Employee 
{
	public String name;
	public int telNo;
	
	
	public String getName() 
	{
		return name;
	}
	
	
	public void setName(String name) 
	{
		this.name = name;
	}
	
	
	public int getTelNo() 
	{
		return telNo;
	}
	
	
	public void setTelNo(int telNo) 
	{
		this.telNo = telNo;
	}
	
}

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Adding the Utility class that calls the Spring API

Next, we are going to create another class named - Utility, which is a simple java class. The Utility class uses the ApplicationContext container(an interface) of Spring Framework by creating its instance using its implemented class FileSystemXmlApplicationContext, which loads the configuration xml file - config.beans.xml.

Utility.java

package decodejava;

import java.util.List;

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

public class Utility {

	public static void main(String[] args) 
	{
		ApplicationContext context = new FileSystemXmlApplicationContext("classpath:config.beans.xml");
		Company company = context.getBean(Company.class);
		List<Employee> listOfEmp = company.getEmployees();
		
		for(Employee emp : listOfEmp)
		{
			System.out.println("Name of employee : " + emp.getName());
			System.out.println("Employee telephone num : "+ emp.getTelNo());
		}
			
	}

}

This Utility.java file does the following tasks -

• Creates the Company bean and initiate it with a value by calling its setter methods i.e. setName and setEmployees()



• Creates a List collection of three Employee beans and initiate it with a value by calling its setter methods i.e. setName() and setTelNo() for each of these Employee beans.



• This List collection collection of Employee beans is injected into Company bean.



• Accesses the Company bean specified in the configuration file by calling the getBean() method of ApplicationContext container.



• Eventually, using the bean of Company class, this class calls the method of Employee class - getName() and getTelNo().

Adding a configuration file

Next, we are going to add a configuration file to our project. This configuration document is an Extensible Markup Language(XML) file, ending with .xml extension and we are going to name file as config.beans.xml.

In this file, we have configured a Company bean with a unique id and it contains a collection of Employee beans.


config.beans.xml

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

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:util="springframework.org/schema/util"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans 
       http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/context
       https://www.springframework.org/context/spring-context.xsd
       ">
           
<bean id="CompanyBean" class="decodejava.Company">
<property name="employees">
	<list>
			<bean class="decodejava.Employee">
			<property name="name" value="Emp1"></property>
			<property name="telNo" value="111111"></property>
			</bean>
			
			<bean class="decodejava.Employee">
			<property name="name" value="Emp2"></property>
			<property name="telNo" value="222222"></property>
			</bean>
			
			<bean class="decodejava.Employee">
			<property name="name" value="Emp3"></property>
			<property name="telNo" value="333333"></property>
			</bean>
	</list>
</property>
</bean>

</beans>

This mapping document has a parent <beans> tag as the root element and its individual child elements, each with a <bean> tag, containing all the attributes such as -

• The id attribute within the <bean> element defines a unique id associated with the bean.
• The class attribute within the <bean> element defines the name of the class of this bean.



The property child element in <bean> tag refers to a property within the Employee class.
• The name child attribute refers to the name of a property in the Employee class i.e. name or telNo.
• The value child attribute refers to the value of this property.



The <list> child tag element in <property> tag is used to configure a List collection property of Employee type in Company class.

Directory Structure of Project

The picture above depicts how and where to arrange classes and interfaces comprising this Spring Project, in a specific directory structure.

Project Folder - SpringWithList is the name of our Project and it is a top-level directory.

This project folder contains a package of our project i.e. decodejava containing three classes -
• A POJO class named Company.java.
• Another POJO class named Employee.java class.
• A class that calls the Spring Framework into action i.e. Utility.java.



• Besides this, the project folder also contains a configuration file i.e. config.beans.xml, used to configure the beans of classes in the project.
  
  
• The project folder also contains all the needed Spring JARs present in the libs folder of Spring Framework installation.

Execution

Finally, after executing Utility class, you will get the following output within the Console window. This output shown below, shows how the Utility class has used the ApplicationContext container of Spring Framework to load the configuration xml file - config.beans.xml, access the beans specified in it, instantiate the Company class and Employee class, by calling their respective setter methods.

Jul 21, 2018 3:06:54 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [config.beans.xml]
Name of employee : Emp1
Employee telephone num : 111111
Name of employee : Emp2
Employee telephone num : 222222
Name of employee : Emp3
Employee telephone num : 333333

This concludes configuring a List collection with the Spring Framework. In the next article, we are going to show you how to configure a Set collection with the Spring Framework.

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