Introduction

In this tutorial, we will refactor a simple Spring Boot application into two files for better code organization. By separating the controller and application startup logic, we adhere to best practices and improve maintainability.

Prerequisites

Before we begin, ensure you have:

• Java Development Kit (JDK) 8 or higher installed
• Spring Boot CLI installed
• Basic understanding of Spring Boot and Maven

Step 1: Initial Setup

Start with the following code in DemoApplication.java:

package com.example.mywebapp;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

    @RestController
    class HelloWorldController {

        @GetMapping("/hello")
        public String hello() {
            return "Hello, World!";
        }
    }
}

Step 2: Create a Separate Controller File

Let’s move the HelloWorldController into its own file HelloWorldController.java:

HelloWorldController.java:

package com.example.mywebapp;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloWorldController {

    @GetMapping("/hello")
    public String hello() {
        return "Hello, World!";
    }
}

Step 3: Refactor DemoApplication.java

In DemoApplication.java, remove the HelloWorldController class and keep the application startup logic:

DemoApplication.java:

package com.example.mywebapp;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

Step 4: Verify and Run Your Application

• Ensure your project structure is correct (src/main/java/com/example/mywebapp).
• Use Maven to build and run your Spring Boot application:bashCopy code./mvnw spring-boot:run

Conclusion

Congratulations! You have successfully refactored a Spring Boot application into two separate files for controller and application startup logic. This approach enhances code clarity and maintainability, making it easier to manage and scale your applications.

Additional Resources

• Spring Boot Documentation
• Spring Initializr

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This structured blog post guides your readers through refactoring a Spring Boot application into separate files for controller and application logic. Feel free to adjust the content based on your audience’s familiarity with Spring Boot and additional details you wish to include!