Spring dependency injection collections

Spring framework provides the facility to inject collection values via constructor or setter method. We can use the following inside the constructor or property element.

1. List.
2. Set.
3. Map.

Syntax (constructor based dependency injection):

<bean id="testBeanId" class="Test">  
   <constructor-arg>  
    <list>  
     <value>value1</value>  
     <value>value2</value>  
     <value>value3</value>  
   </list>  
  </constructor-arg>  
</bean>

Syntax (setter based dependency injection):

<bean id="testBeanId" class="Test">  
   <property name="testProperty">  
    <list>  
     <value>value1</value>  
     <value>value2</value>  
     <value>value3</value>  
   </list>  
  </property>  
</bean>

Example Explanation:

We have created two beans “Student” and “Address”. Student class requires an Address class object. In spring configuration file we define Address bean objects and pass these objects as a list in constructor-arg.

Example:

Student.java

package com.w3schools.business;
 
import java.util.List;
 
/**
 * This class will be used as a bean class.
 * @author w3schools
 */
public class Student {
	private String name;
	private String rollNo;
	private String className;
	private List<Address> address;
 
	public Student(List<Address> address){
		this.address = (List<Address>) address;
	}
 
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getRollNo() {
		return rollNo;
	}
	public void setRollNo(String rollNo) {
		this.rollNo = rollNo;
	}
	public String getClassName() {
		return className;
	}
	public void setClassName(String className) {
		this.className = className;
	}
	public List<Address> getAddress() {
		return address;
	}	
}

Address.java

package com.w3schools.business;
 
/**
 * This class will be used as a bean class.
 * @author w3schools
 */
public class Address {
	private String addLine;
	private String city;
	private String state;
	private String country;
 
	public String getAddLine() {
		return addLine;
	}
	public void setAddLine(String addLine) {
		this.addLine = addLine;
	}
	public String getCity() {
		return city;
	}
	public void setCity(String city) {
		this.city = city;
	}
	public String getState() {
		return state;
	}
	public void setState(String state) {
		this.state = state;
	}
	public String getCountry() {
		return country;
	}
	public void setCountry(String country) {
		this.country = country;
	}	
}

applicationContext.java

<?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="student" class="com.w3schools.business.Student">
   	   <property name="name" value="Jai"/>
       <property name="rollNo" value="MCA/07/06"/>
       <property name="className" value="MCA"/>
       <constructor-arg>
        <list>
      	 <ref bean="address1"/>
         <ref bean="address2"/>
        </list>
       </constructor-arg>
   </bean>
 
    <bean id="address1" class="com.w3schools.business.Address">
       <property name="addLine" value="Test address1"/>
       <property name="city" value="Gurgaon"/>
       <property name="state" value="Haryana"/>
       <property name="country" value="India"/>
    </bean>
 
    <bean id="address2" class="com.w3schools.business.Address">
       <property name="addLine" value="Test address2"/>
       <property name="city" value="Panipat"/>
       <property name="state" value="Haryana"/>
       <property name="country" value="India"/>
    </bean>
 
</beans>

Test.java

package com.w3schools.business;
 
import java.util.List;
 
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
 
public class Test {
 public static void main(String[] args) {
	//Get ApplicationContext using spring configuration file.
	ApplicationContext context = 
	  new ClassPathXmlApplicationContext("applicationContext.xml");
 
	//Get Student bean object from ApplicationContext instance. 
	Student student = (Student) context.getBean("student");
 
	//Process Student Object.
	System.out.println("Student info: ");
	System.out.println("Name: " + student.getName());
	System.out.println("RollNo: " + student.getRollNo());
	System.out.println("Class: " + student.getClassName());
 
	//Get Address from Student Object.
	List<Address> studentAddressList = student.getAddress();
 
	//Declare program counter.
	int addressCounter = 1;
 
	//Iterate Address List.
	for (Address studentAddress : studentAddressList) {
	  //Process Address Object.
	  System.out.println("Student Address " +addressCounter+ ": ");
	  System.out.println("Address Line: "+studentAddress.getAddLine());
	  System.out.println("City: " + studentAddress.getCity());
          System.out.println("State: " + studentAddress.getState());
	  System.out.println("Country: " + studentAddress.getCountry());
	  addressCounter++;
       }			
  } 
}

Output:

Student info: 
Name: Jai
RollNo: MCA/07/06
Class: MCA
Student Address 1: 
Address Line: Test address1
City: Gurgaon
State: Haryana
Country: India
Student Address 2: 
Address Line: Test address2
City: Panipat
State: Haryana
Country: India