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Spring @Qualifier with Constructors

In this topic, we are using the @Qualifier annotation with a constructor to specify the dependency instance. We can specify the @Qualifier annotation on individual constructor arguments or method parameters, as shown in the following example:

Let's create a spring project, this project is a Maven-Based Spring Project and contains the following files.

  • App.java

  • AppConfig.java

  • Award.java

  • BookerAward.java

  • NationalAward.java

  • PulitzerAward.java

  • FictionWriter.java

  • TechnicalWriter.java

  • Writer.java

  • pom.xml

Project Structure:

Files Source Code:

//App.java

This file contains the code to create an IOC container for our application. The AnnotationConfigApplicationContext class is used to create an object for application context.

package com.studytonight.community;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
public class App {
	public static void main(String[] args) {
		
		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
		Writer writer = context.getBean("fictionWriter", Writer.class);
		writer.write();
		writer.getAward();
		// Close the context
		context.close();
	}
}

// AppConfig.java

This is a configuration file in Java which is an alternate of the applicationContext.xml file that we created for the XML-based configuration example. The @Configuration annotation indicates that this is not a simple class but a configuration class and the @ComponentScan annotation is used to indicate the component's location in our spring project.

package com.studytonight.community;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
@Configuration
@ComponentScan("com.studytonight.community")
public class AppConfig {

}

// Award.java

This is an interface Award that contains a award() abstract method. Each class that implements this interface will have to override the award() method.

package com.studytonight.community;
public interface Award {
	void award();

}

// BookerAward.java

This is a component class that is marked using the @Component annotation and implements the Award interface.

package com.studytonight.community;
import org.springframework.stereotype.Component;
@Component
public class BookerAward implements Award {
	@Override
	public void award() {
		
		System.out.println("You got booker prize...");
	}
}

// FictionWriter.java

This is another component class that is marked using the @Component annotation and implements the Writer interface.

package com.studytonight.community;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Component;

@Component
public class FictionWriter implements Writer {
	private Award award;
		
	@Autowired
	public FictionWriter(@Qualifier("bookerAward") Award award) {
		this.award = award;
	}
	@Override
	public void write() {
		
		System.out.println("Write Fiction Novels...");
	}
	@Override
	public void getAward() {
		
		award.award();
	}
}

// NationalAward.java

This is another component class that is marked using the @Component annotation and implements the Award interface.

package com.studytonight.community;
import org.springframework.stereotype.Component;

@Component
public class NationalAward implements Award{	
	public void award() {		
		System.out.println("Your Writting got National Award!");
	}
}

// PulitzerAward.java

This is another component class that is marked using the @Component annotation and implements the Award interface.

package com.studytonight.community;
import org.springframework.stereotype.Component;
@Component
public class PulitzerAward implements Award {

	@Override
	public void award() {
		
		System.out.println("You have won Pulitzer Award.");
	}
}

// TechnicalWriter.java

This is another component class that is marked using the @Component annotation and implements the Writer interface.

package com.studytonight.community;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Component;

@Component
public class TechnicalWriter implements Writer{

	private Award award;

	@Autowired
	public TechnicalWriter(@Qualifier("pulitzerAward") Award award) {
		this.award = award;
	}
	@Override
	public void write() {
		
		System.out.println("Write technical stuffs...");
	}
	@Override
	public void getAward() {
		award.award();		
	}
}

// Writer.java

package com.studytonight.community;
public interface Writer {
	
	void write();
	void getAward();
}

// pom.xml

This file contains all the dependencies of this project such as spring jars, servlet jars, etc. Put these dependencies into your project to run the application.

<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.studytonight</groupId>
  <artifactId>springproject</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <dependencies>
  <!-- https://mvnrepository.com/artifact/org.springframework/spring-web -->
  <dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-core</artifactId>
			<version>${spring.version}</version>
		</dependency>
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-context</artifactId>
			<version>${spring.version}</version>
		</dependency>
	</dependencies>
	<properties>
		<spring.version>5.2.8.RELEASE</spring.version>
	</properties>
  <build>
    <sourceDirectory>src</sourceDirectory>
    <plugins>
      <plugin>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.8.1</version>
        <configuration>
          <source>1.8</source>
          <target>1.8</target>
        </configuration>
      </plugin>
    </plugins>
    
  </build>
</project>

Run the Application

After successfully updating these two files into the project run the application and you will get the output as below.


Write Fiction Novels...
You got booker prize...



About the author:
I am a Java developer by profession and Java content creator by passion. I have over 5 years of experience in Java development and content writing. I like writing about Java, related frameworks, Spring, Springboot, etc.