Spring @Configuration annotation example

Spring @Configuration annotation helps in Spring annotation based configuration. @Configuration annotation indicates that a class declares one or more @Bean methods and may be processed by the Spring container to generate bean definitions and service requests for those beans at runtime.

Since spring 2, we were writing our bean configurations to xml files. But Spring 3 gave the freedom to move bean definitions out of xml files. we can give bean definitions in Java files itself. This is called Spring Java Config feature (using @Configuration annotation).

1. Spring @Configuration annotation usage

Use @Configuration annotation on top of any class to declare that this class provides one or more @Bean methods and may be processed by the Spring container to generate bean definitions and service requests for those beans at runtime.

@Configuration
public class AppConfig {

    @Bean(name="demoService")
    public DemoClass service() 
    {
       
    }
}

2. Spring @Configuration annotation example

To understand @Configuration annotation usage, let’s see it in action.

2.1. Create maven project

mvn archetype:generate 
    -DgroupId=com.howtodoinjava.core 
    -DartifactId=springCoreTest
    -DarchetypeArtifactId=maven-archetype-quickstart 
    -DinteractiveMode=false

mvn eclipse:eclipse

2.2. Update Spring dependencies

Update maven dependencies. I have added Spring 5 deendencies.

<properties>
    <spring .version>5.0.6.RELEASE</spring>
</properties>

<!-- Spring 5 dependencies -->
<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>

<!-- For JavaConfig -->
<dependency>
    <groupid>cglib</groupid>
    <artifactid>cglib</artifactid>
    <version>2.2.2</version>
</dependency>

2.3. Create spring beans

public interface DemoManager {
    public String getServiceName();
}

public class DemoManagerImpl implements DemoManager
{
    @Override
    public String getServiceName()
    {
        return "My first service with Spring 3";
    }
}

2.4. Spring configuration class with @Configuration annotation

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import com.howtodoinjava.core.beans.DemoManager;
import com.howtodoinjava.core.beans.DemoManagerImpl;

@Configuration
public class ApplicationConfiguration {

    @Bean(name="demoService")
    public DemoManager helloWorld() 
    {
        return new DemoManagerImpl();
    }
}

3. Demo

Lets write the test code and run. This should be able to configure bean and we should be able to use it.

package com.howtodoinjava.core.verify;

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import com.howtodoinjava.core.beans.DemoManager;
import com.howtodoinjava.core.config.ApplicationConfiguration;

public class VerifySpringCoreFeature
{
    public static void main(String[] args)
    {
        ApplicationContext context = new AnnotationConfigApplicationContext(ApplicationConfiguration.class);

        DemoManager  obj = (DemoManager) context.getBean("demoService");

        System.out.println( obj.getServiceName() );
    }
}

Happy Leaning !!