Till now, we inject the dependencies from the spring configuration file as simple types like primitives or wrapper classes (Objects) through the <properties> tag. But in Spring we can define the dependencies for three different types.

• Simple Type
• Object Type and
• Collection Type

In the all previous Spring examples, we have injected the dependencies by using the simple (normal properties) and Object (any property as a type of object). But in this tutorial, we are going to implement spring collection dependency.

Spring Collection Dependency :

In spring we can inject the dependencies as a type of collection. But we have some limitations on that. i.e. Spring container can inject collection type, if and only if the collection type is one of the below 4.

• java.util.List
• java.util.Set
• java.util.Map
• java.util.Properties

We can say that above four are spring collection types. Apart from those four types, we can not implement any collection type in spring.

Spring Collection List Example :

If the dependency type is java.util.List, then in spring configuration file we should configure the List type with <list> tag.

If that list contains the normal properties like String or int or float etc.. we can define the values by using the <value> tag.

If the list contains the Object type, we can assign the bean to that object by using the <ref> tag.

Below is the example for Lists contains normal properties and Object types.

Project Structure :

Spring Maven Dependency:

<dependencies>
    <!-- Spring -->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>${spring-framework.version}</version>
    </dependency>

    <!-- Logging with SLF4J & LogBack -->
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-api</artifactId>
        <version>${slf4j.version}</version>
        <scope>compile</scope>
    </dependency>
    <dependency>
        <groupId>ch.qos.logback</groupId>
        <artifactId>logback-classic</artifactId>
        <version>${logback.version}</version>
        <scope>runtime</scope>
    </dependency>

Spring Collection Beans :

Employee.Java

package com.onlinetutorialspoint.bean;

public class Employee {
    private int empId;
    private String empName;
    

    public int getEmpId() {
        return empId;
    }

    public void setEmpId(int empId) {
        this.empId = empId;
    }

    public String getEmpName() {
        return empName;
    }

    public void setEmpName(String empName) {
        this.empName = empName;
    }

}

Department.java

package com.onlinetutorialspoint.bean;

import java.util.List;

public class Department {
    private int deptId;
    private String deptName;
    private List<Employee> employees;
    private List<String> telephoneNumbers;

    public int getDeptId() {
        return deptId;
    }

    public void setDeptId(int deptId) {
        this.deptId = deptId;
    }

    public String getDeptName() {
        return deptName;
    }

    public void setDeptName(String deptName) {
        this.deptName = deptName;
    }

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

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

    public void setTelephoneNumbers(List<String> telephoneNumbers) {
        this.telephoneNumbers = telephoneNumbers;
    }    

}

Spring Collection Configuration :

spring configuration.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:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.0.xsd
    http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd">
    <bean id="deptBean" class="com.onlinetutorialspoint.bean.Department">
        <property name="deptId" value="20501" />
        <property name="deptName" value="IT" />
        <property name="telephoneNumbers">
            <list>
                <value>0409696969</value>
                <value>0409898989</value>
            </list>
        </property>
        <property name="employees">
            <list>
                <ref bean="empBean" />
                <ref bean="empBean2" />
                <ref bean="empBean3" />
            </list>
        </property>
    </bean>
    <bean id="empBean" class="com.onlinetutorialspoint.bean.Employee">
        <property name="empId" value="101" />
        <property name="empName" value="Chandra Shekhar" />
    </bean>
    <bean id="empBean2" class="com.onlinetutorialspoint.bean.Employee">
        <property name="empId" value="102" />
        <property name="empName" value="Robert" />
    </bean>
    <bean id="empBean3" class="com.onlinetutorialspoint.bean.Employee">
        <property name="empId" value="103" />
        <property name="empName" value="John" />
    </bean>

</beans>

Run the Application :

Main.java

import java.util.List;

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

import com.onlinetutorialspoint.bean.Department;
import com.onlinetutorialspoint.bean.Employee;

public class Main {
    public static void main(String args[]) {
        ApplicationContext context = new ClassPathXmlApplicationContext("springconfiguration.xml");
        Department department = (Department) context.getBean("deptBean");
        System.out.println("DeptId : " + department.getDeptId());
        System.out.println("DeptName : " + department.getDeptName());
        List<String> telephoneNumbers = department.getTelephoneNumbers();
        int i = 1;
        for (String number : telephoneNumbers) {
            System.out.println("Telephone " + i + " :" + number);
            i++;
        }
        System.out.println("===================");
        System.out.println("Employees Under Department No : "+department.getDeptId());
        List<Employee> employees = department.getEmployees();
        for (Employee employee : employees) {
            System.out.println("Employee Id : " + employee.getEmpId());
            System.out.println("Empoyee Name : " + employee.getEmpName());
        }

    }
}

Output :

DeptId : 20501
DeptName : IT
Telephone 1 :0409696969
Telephone 2 :0409898989
===================
Employees Under Department No : 20501
Employee Id : 101
Empoyee Name : Chandra Shekhar
Employee Id : 102
Empoyee Name : Robert
Employee Id : 103
Empoyee Name : John

Happy Learning 🙂