Constructor Dependency Injection with Map of String

In some scenarios, we may need to inject a map of strings to an object.
In such cases, we inject a map of string through a constructor.

Consider the example where Person has phone numbers which can be of type mobile or landline.

In this case, let us use Map which stores phone type as a key and phone number as a value.

Let us see the same in spring through Constructor Dependency Injection

Create a class called Person

It contains 3 attributes id,name and phoneNos where phoneNos is a Map.

It also contains showPhoneNos() method to display the phone numbers injected to the person object.

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package com.kb.di;
 
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
 
public class Person {
    private int id;
    private String name;
    private Map<String, String> phoneNos;
 
    public Person(int id, String name, Map<String, String> phoneNos) {
        super();
        this.id = id;
        this.name = name;
        this.phoneNos = phoneNos;
    }
    public void showPhoneNos(){
    for (Entry<String, String> entry : phoneNos.entrySet()) {
        System.out.println(entry.getKey()+"-->"+entry.getValue());
    }
        
    }
    }
package com.kb.di;

import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

public class Person {
	private int id;
	private String name;
	private Map<String, String> phoneNos;

	public Person(int id, String name, Map<String, String> phoneNos) {
		super();
		this.id = id;
		this.name = name;
		this.phoneNos = phoneNos;
	}
	public void showPhoneNos(){
	for (Entry<String, String> entry : phoneNos.entrySet()) {
		System.out.println(entry.getKey()+"-->"+entry.getValue());
	}
		
	}
	}

Create a spring bean definition file

In this file, we used < constructor-arg > tag with < map > to define the phoneNos
< entry > tag is used to inject Map’s key and value.

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<?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-3.2.xsd">
  
 <bean id="person" class="com.kb.di.Person">  
    <constructor-arg value="1" type="int"/>
    <constructor-arg value="Raj"/> 
    <constructor-arg>
    <map>
    <entry key="mobile" value="9999967891"/>
    <entry key="landline" value="080789345"/>
    </map>
    </constructor-arg> 
 </bean>
</beans>
<?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-3.2.xsd">
  
 <bean id="person" class="com.kb.di.Person">  
	<constructor-arg value="1" type="int"/>
	<constructor-arg value="Raj"/> 
	<constructor-arg>
	<map>
	<entry key="mobile" value="9999967891"/>
	<entry key="landline" value="080789345"/>
	</map>
	</constructor-arg> 
 </bean>
</beans>

Create a pom.xml file

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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
 
  <groupId>Spring</groupId>
  <artifactId>SpringCore</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>
 
  <name>SpringCore</name>
  <url>http://maven.apache.org</url>
 
  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>
 
  <dependencies>
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-core</artifactId>
    <version>4.2.4.RELEASE</version>
</dependency>
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-context</artifactId>
    <version>4.2.4.RELEASE</version>
</dependency>
  
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
</project>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>Spring</groupId>
  <artifactId>SpringCore</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>SpringCore</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
  <dependency>
	<groupId>org.springframework</groupId>
	<artifactId>spring-core</artifactId>
	<version>4.2.4.RELEASE</version>
</dependency>
  <dependency>
	<groupId>org.springframework</groupId>
	<artifactId>spring-context</artifactId>
	<version>4.2.4.RELEASE</version>
</dependency>
  
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
</project>

Create a ConstructorDI class

This class loads the spring beans using application context and calls the person class method to display the phone numbers.

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package com.kb.di;
 
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.Resource;
 
public class ConstructorDI {
    
    public static void main(String[] args) {
        ApplicationContext applicationContext=new ClassPathXmlApplicationContext("beans.xml");  
        Person person = (Person)applicationContext.getBean("person");
        person.showPhoneNos();
    
        
    }
 
}
package com.kb.di;

import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.Resource;

public class ConstructorDI {
	
	public static void main(String[] args) {
        ApplicationContext applicationContext=new ClassPathXmlApplicationContext("beans.xml");  
        Person person = (Person)applicationContext.getBean("person");
        person.showPhoneNos();
    
        
	}

}

Run the ConstructorDI class and see the output as below

Download this project SpringDIWithMapOfStrings.zip

About the Author

Karibasappa G C (KB)
Founder of javainsimpleway.com
I love Java and open source technologies and very much passionate about software development.
I like to share my knowledge with others especially on technology 🙂
I have given all the examples as simple as possible to understand for the beginners.
All the code posted on my blog is developed,compiled and tested in my development environment.
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