Spring Boot Devtools is a powerful tool that significantly improves the development experience by providing features like automatic restarts, live reload, and configurations that are optimized for development. In this blog post, we’ll explore how to set up and use Spring Boot Devtools to speed up your development workflow.

Why Use Spring Boot Devtools?

Spring Boot Devtools enhances the development process in several ways:

  1. Automatic Restarts: Automatically restarts your application whenever files on the classpath change, saving you the hassle of manually restarting the server.
  2. Live Reload: Integrates with LiveReload to refresh the browser when resources change, providing instant feedback on your changes.
  3. Development-Time Configurations: Applies specific settings that make development easier, like disabling template caching and enabling debug logging.

Setting Up Spring Boot Devtools

Adding Devtools Dependency

First, you need to add the Spring Boot Devtools dependency to your project. This can be done by adding the following dependency to your pom.xml if you are using Maven:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-devtools</artifactId>
    <scope>runtime</scope>
</dependency>

Or to your build.gradle if you are using Gradle:

developmentOnly 'org.springframework.boot:spring-boot-devtools'

Configuring Devtools

Spring Boot Devtools is designed to work out of the box with sensible defaults, but there are some configurations you might want to adjust based on your needs.

Automatic Restart

Automatic restart is a key feature of Devtools. By default, it monitors your classpath for changes and restarts your application when necessary. You can customize this behavior by setting the spring.devtools.restart properties in your application.properties or application.yml.

For example, to disable automatic restart, you can add:

spring.devtools.restart.enabled=false

Live Reload

Devtools includes an embedded server for the LiveReload protocol. If you have a LiveReload browser extension installed, it will automatically refresh your browser when files change.

You can disable this feature if needed:

spring.devtools.livereload.enabled=false

Remote Development

Devtools also supports remote development, allowing you to tunnel HTTP traffic over a secure connection to your local machine. This is useful for testing how your application behaves in different environments.

To enable remote devtools, add the following to your application.properties:

spring.devtools.remote.secret=mysecret

And run your application with the -Dspring.devtools.remote.secret=mysecret VM option.

Using Devtools in Your Workflow

Once Devtools is set up, you can take advantage of its features to streamline your development process.

  1. Automatic Restarts: Modify your Java code or configuration files, and Devtools will automatically restart your application, applying the changes immediately.
  2. Live Reload: Edit your HTML, CSS, or JavaScript files, and see the changes reflected in your browser without a manual refresh.
  3. Development-Time Configurations: Enjoy faster development with non-cached templates, debug logging, and other developer-friendly settings.

Example: Using Devtools with a Spring Boot Application

Let’s create a simple Spring Boot application to demonstrate how Devtools enhances the development process.

Step 1: Create a Spring Boot Application

Create a new Spring Boot project using Spring Initializr or your preferred method. Add the necessary dependencies, including Spring Web and Devtools.

Step 2: Add Devtools Dependency

Ensure your pom.xml or build.gradle includes the Devtools dependency as described above.

Step 3: Create a Simple Controller

Create a simple controller to handle HTTP requests. For example:

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

@RestController
public class HelloController {

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

Step 4: Run Your Application

Run your application and navigate to http://localhost:8080/hello to see the output.

Step 5: Make Changes and See Instant Feedback

Modify the return statement in the hello() method to something else, like "Hello, Devtools!". Save the file, and you should see your application automatically restart. Refresh your browser to see the updated message.

Step 6: Enable Live Reload

Install a LiveReload browser extension (if you haven’t already), and make changes to your HTML, CSS, or JavaScript files. The browser will automatically refresh to reflect your changes.

Conclusion

Spring Boot Devtools is an invaluable tool for developers, providing features that speed up development and reduce the friction of constant restarts and manual refreshes. By incorporating Devtools into your workflow, you can focus more on writing code and less on managing your development environment.