How to Enable Hot Reload and Remote Debugging in Spring Boot with DevTools

Introduction

spring-boot-devtools

is an official Spring Boot tool that enables hot deployment and remote debugging. It uses two class loaders: a base loader for unchanged classes and a restart loader for application classes, making restarts faster.

Hot Deployment

We integrate devtools into a Spring Boot project to demonstrate hot deployment.

Add the devtools dependency to pom.xml (optional true).

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-devtools</artifactId>
  <optional>true</optional>
</dependency>

Add a test controller that returns a message.

@Tag(name = "TestController", description = "SpringBoot Dev Tools测试")
@Controller
@RequestMapping("/test")
public class TestController {
    @Operation(summary = "测试修改")
    @RequestMapping(value = "/first", method = RequestMethod.GET)
    @ResponseBody
    public CommonResult first() {
        String message = "返回消息";
        return CommonResult.success(null, message);
    }
}

Run the application; Swagger UI can be used to call the test endpoint.

{
  "code": 200,
  "message": "返回消息",
  "data": null
}

Enable automatic build in the IDE when it loses focus so changes trigger restart.

Modify the message variable in the controller; after focus loss the new message is applied automatically.

{
  "code": 200,
  "message": "返回消息（已修改）",
  "data": null
}

Remote Debugging

DevTools also supports remote debugging. The application is packaged into a Docker container and run.

Add configuration to the Spring Boot Maven plugin to avoid excluding devtools.

<plugin>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-maven-plugin</artifactId>
  <configuration>
    <excludeDevtools>false</excludeDevtools>
  </configuration>
</plugin>

Set remote access password in application.yml.

spring:
  devtools:
    remote:
      secret: macro666

Build Docker image and run:

docker run -p 8088:8088 --name spring-devtools -d spring-examples/spring-devtools:1.0-SNAPSHOT

Create a Remote Spring Application run configuration in the IDE, using org.springframework.boot.devtools.RemoteSpringApplication and the container URL.

Console output shows successful remote connection.

2025-07-22T10:22:13.452+08:00  INFO 34364 --- [spring-devtools] o.s.b.devtools.RemoteSpringApplication : Starting RemoteSpringApplication v3.4.2 using Java 17.0.9 with PID 34364
2025-07-22T10:22:13.454+08:00  INFO 34364 --- [spring-devtools] o.s.b.devtools.RemoteSpringApplication : No active profile, falling back to 1 default profile: "default"
2025-07-22T10:22:13.573+08:00  INFO 34364 --- [spring-devtools] o.s.b.d.a.OptionalLiveReloadServer : LiveReload server is running on port 35729
2025-07-22T10:22:13.584+08:00  INFO 34364 --- [spring-devtools] o.s.b.devtools.RemoteSpringApplication : Started RemoteSpringApplication in 0.352 seconds (process running for 0.739)

Modify the controller's message variable; after manual build the remote service restarts and returns the updated message.

{
  "code": 200,
  "message": "返回消息（远程调试）",
  "data": null
}

Conclusion

Spring Boot’s devtools provides fast hot reload and remote debugging, making development more efficient.

Source code: https://github.com/macrozheng/spring-examples/tree/master/spring-devtools