Spring – Constructor Injection with Map

In the constructor injection, the dependency injection will be injected with the help of constructors. Now to set the dependency injection as constructor dependency injection(CDI) in bean, it is done through the bean-configuration file For this, the property to be set with the constructor dependency injection is declared under the <constructor-arg> tag in the bean-config file.

Illustration:

Java

package com.geeksforgeeks.org;

import com.geeksforgeeks.org.IGeek;

public class GFG {

    // Creating an object of the interface IGeek
    IGeek geek;

    // Constructor to set the CDI
    GFG(IGeek geek)
    {

        // This keyword refers to current instance itself
        this.geek = geek;
    }
}

Setting the CDI in the bean-config File

XML

<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-2.5.xsd">

    <bean id="GFG" class="com.geeksforgeeks.org.GFG">
        <constructor-arg>
            <bean class="com.geeksforgeeks.org.impl.CsvGFG" />
        </constructor-arg>
    </bean>

<bean id="CsvGFG" class="com.geeksforgeeks.org.impl.CsvGFG" />
<bean id="JsonGFG" class="com.geeksforgeeks.org.impl.JsonGFG" />

</beans>

Constructor Injection with Map

Spring frameworks provide us the facility to inject collection values via constructor in our spring application. The following collections can be used inside the <constructor-arg> tag:

• list
• set
• map

Implementation: In the following example, we will see constructor injection with Map. The map will have both key and value as String.

A. Company.java

A company can have multiple employees. Each employee will have an employee ID and department. The ’employees’ map will store employee IDs as key and the respective departments will be stored as values.

Example:

Java

// Java Program to illustrate Company Class

package com.geeksforgeeks.org;

// Importing required classes
import java.util.*;
import java.util.Map.Entry;

// Class
public class Company {

    // Class member variables
    private Map<String, String> employees;

    // Constructor
    public Company(Map<String, String> employees)
    {
        // this keyword refers to current instance itself
        this.employees = employees;
    }

    // Method
    public void display()
    {
        for (Map.Entry<String, String> entry :
             employees.entrySet()) {

            System.out.println(
                "Employee Id ->" + entry.getKey() + ","
                + " Department->" + entry.getValue());
        }
    }
}

B. applicationContext.xml

The entry attribute of map will be used to store key and value information.

Example:

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:p="http://www.springframework.org/schema/p"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
     http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">



     <bean id="company" class="com.geeksforgeeks.org.Company">
        <constructor-arg>
            <map>
                <entry key="101"  value="Software development"></entry>
                <entry key="102" value="Software testing"></entry>
                <entry key="103" value="Security"></entry>
            </map>
        </constructor-arg>
    </bean>

</beans>

C. Test.java

Java

// Java Program to Illustrate Application Class

package com.geeksforgeeks.org;

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;

// Application class
// Main class
public class Test {

    // Main driver method
    public static void main(String[] args)
    {
        // Creating a class path resource
        Resource resource = new ClassPathResource(
            "applicationContext.xml");

        // Creating an object of BeanFactory class
        BeanFactory factory = new XmlBeanFactory(resource);

        // Creating an object of Employee class
        Employee c = (Employee)factory.getBean("company");

        // Calling print() method inside main() method
        c.display();
    }
}

Output:

Employee ID -> 101, Department -> Software development
Employee ID -> 102, Department -> Software testing
Employee ID -> 103, Department -> Security