[Spring] What is Java Config Bean?

Java Config Bean 코드로 이해하기

Development Process

1. Create @Configuration class
2. Define @Bean method to configure the bean
3. Inject the bean into our controller

Step 1: Create a Java class and annotate as @Configuration

import org.springframework.context.annotation.Configuration;  
  
@Configuration  
public class SportConfig {  
  

}

Step 2: Define @Bean method to configure the bean

import 
import org.springframework.context.annotation.Bean;org.springframework.context.annotation.Configuration;  
  
@Configuration  
public class SportConfig {  
  
    @Bean()  // The bean id defaults to the method name
    public Coach swimCoach(){  
        return new SwimCoach();  
    }  
}

Step 3: Injeact the bean into our controller

@RestController  
public class DemoController {  
  
    private Coach myCoach;  
  
    @Autowired  
    public DemoController(  
		    //Inject the bean using the bean Id
            @Qualifier("swimCoach") Coach theCoach){  
        System.out.println("In constructor: " + getClass().getSimpleName());  
        myCoach = theCoach;  
    }  
  
  
    }

Use case for @Bean

• You may wonder…
  • Using the “new” keyword … is that it??
  • Why not just annotate the class with @Component?
• Make an existing third-party class available to Spring framework
• You may not have access to the source code of third-party class
• However, you would like to use the third-party class as a Spring bean

Real-World Project Example

• Our project used Amazon web service(AWS) to store documents
• We wanted to use the AWS S3 client as a Spring Bean in our app
• The AWS S3 client code is part of AWS SDK
  • We can’t modify the AWS SDK source code
  • We can’t just add @Component
• However, we can configure it as a Spring bean using @Bean

Configure AWS S3 Client using @Bean

@Configuration
public class DocumentConfig{

	@Bean
	public S3client remoteClient(){
	//create an S3 client to connect to AWS S3
	ProfileCredentialsProvider credentialsProvider =   
	ProfileCredentialsProvider.create();
	Region region = Region.US_EAST_1;
	S3Client s3Client = S3Client.builder()
	.region(region)
	.credentialsProvider(credentialsProvider)
	.build();
return s3Client;
	
	}

}

Inject the S3Client as a bean

@Component
public class DocumentsService{
	private S3ClientService {
	@Autowired
	public DocumentsService(S3Client theS3client){
		s3Client = theS3client;
	}
	}
}

• You have this private S3 client, and then you can auto-wire in this ~~~

Store our documents in S3

@Component
public class DocumentsService {

	private S3Client s3Client;

	@Autowired
	public DocumentsService(S3Client theS3Client){
		s3Client = theS3Client;
	}
	public void processDocument(Document theDocument){
		// get the document input stream and file size
		// Store document in AWS S3
		// Create a put request for the object
		PutObjectRequest putObjectRequest = PutObjectRequest.builder()
			.bucket(bucketName)
			.key(subDirectory + "/" +fileName)
			.acl(ObjectCannedACL.BUCKET_OWNER_FULL_CONTROL).build();
		// perform the putObject operation to AWS S3 .. using our autowired bean
		s3Client.putObject(putObjectRequest, RequestBody, formInputStream(fileInputStream, contentLength));
	}


}

간단히

package com.luv2code.springcoredemo.config;  
  
import com.luv2code.springcoredemo.common.Coach;  
import com.luv2code.springcoredemo.common.SwimCoach;  
import org.springframework.context.annotation.Bean;  
import org.springframework.context.annotation.Configuration;  
  
@Configuration  
public class SportConfig {  
  
    @Bean("aquatic")  
    public Coach swimCoach(){  
        return new SwimCoach();  
    }  
}

package com.luv2code.springcoredemo.rest;  
  
import com.luv2code.springcoredemo.common.Coach;  
import org.springframework.beans.factory.annotation.Autowired;  
import org.springframework.beans.factory.annotation.Qualifier;  
import org.springframework.web.bind.annotation.GetMapping;  
import org.springframework.web.bind.annotation.RestController;  
  
@RestController  
public class DemoController {  

    private Coach myCoach;  

    @Autowired  
    public DemoController(  
            @Qualifier("aquatic") Coach theCoach){  
        System.out.println("In constructor: " + getClass().getSimpleName());  
        myCoach = theCoach;  
    }  
  
    @GetMapping("/dailyworkout")  
    public String getDailyWorkout(){  
        return myCoach.getDailyWorkout();  
    }  
  
  
    }

• bean id 디폴트 값은 메소드 이름

Wrap up

• We could use the Amazon S3 Client in our Spring application
• The Amazon S3 Client class was not originally annotated with @Component
• However, we configured the S3 Client as a Spring Bean using @Bean
• It is now a spring Bean and we can inject it into other services of our application
• Make an existing third-party class available to Spring framework