Spring Boot DevTools & Live Reload

Table of Contents

1. Introduction
2. What is Spring Boot DevTools?
3. Key Features of DevTools
4. Setting Up Spring Boot DevTools
5. Live Reload Explained
6. Using Live Reload with a Browser
7. Auto-Restart vs. Live Reload
8. Customizing DevTools Behavior
9. Use Cases and Benefits
10. Common Issues and Troubleshooting
11. Conclusion

1. Introduction

Spring Boot DevTools is a powerful module that enhances the development experience by offering productivity-boosting features such as automatic restarts, live reloads, and advanced debugging support. These features eliminate the need to manually restart the application after every change, significantly speeding up the development workflow.

2. What is Spring Boot DevTools?

Spring Boot DevTools is a development-time only dependency that helps developers build applications more efficiently. It is not intended to be included in production builds and should only be used during development.

Its primary features include:

• Automatic application restart when files on the classpath change
• Live reload integration with the browser
• Property defaults for development
• Fast restart using classloader separation

3. Key Features of DevTools

• Automatic Restart: Monitors classpath files and restarts the application upon changes.
• Live Reload: Automatically refreshes the browser when HTML/CSS/JS content changes.
• Disabling Caching: Disables template and static resource caching during development.
• Remote Debugging: Enables secure remote development sessions.
• Global Settings: Allows shared DevTools configurations across projects.

4. Setting Up Spring Boot DevTools

Add the DevTools dependency to your project. If you’re using Maven:

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

For Gradle:

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

Note: Marking it as developmentOnly or runtime ensures it’s not packaged in the production artifact.

5. Live Reload Explained

Live Reload allows you to automatically refresh the browser window whenever changes are made to static resources like HTML, CSS, or JavaScript.

DevTools embeds a LiveReload server on port 35729. When changes are detected, the server notifies connected browsers to refresh.

6. Using Live Reload with a Browser

To enable Live Reload:

1. Install a LiveReload browser extension (available for Chrome, Firefox).
2. Enable the extension and start your Spring Boot application.
3. Make changes to any static file like .html, .css, or .js.
4. Your browser should refresh automatically.

Alternatively, use Spring Boot + Thymeleaf or any other templating engine to see template updates in real time.

7. Auto-Restart vs. Live Reload

• Auto-Restart: Triggers when a .class file changes. Spring Boot restarts the application using a separate classloader for speed.
• Live Reload: Triggers when static resources (e.g., .html, .css) change. Reloads the web page in the browser but doesn’t restart the backend.

Both features are complementary.

8. Customizing DevTools Behavior

You can disable or fine-tune features using application.properties or application.yml:

propertiesCopyEdit# Disable restart
spring.devtools.restart.enabled=false

# Enable LiveReload
spring.devtools.livereload.enabled=true

# Change trigger file paths
spring.devtools.restart.additional-paths=src/main/java,src/main/resources

Spring Boot monitors src/main/java and src/main/resources by default, but you can add more paths if needed.

9. Use Cases and Benefits

• Web developers: See UI changes without reloading manually.
• Backend developers: Quickly test updated logic or configurations.
• Full-stack developers: Seamless feedback loop for both client and server changes.
• Educational use: Ideal for coding demonstrations or learning platforms where real-time feedback is important.

10. Common Issues and Troubleshooting

• LiveReload not working: Ensure the browser extension is installed and not blocked by browser security.
• App restarts unexpectedly: Check for file watchers on non-code directories.
• High memory use: Consider turning off automatic restarts if unnecessary.

Check your IDE’s automatic build settings. IntelliJ IDEA and Eclipse both support auto-compiling changes that trigger restarts.

11. Conclusion

Spring Boot DevTools significantly enhances developer productivity by removing repetitive tasks like restarting the server or refreshing the browser. By leveraging automatic restarts and live reload, you can focus more on development and less on setup or environment concerns. It’s a must-have tool for Spring Boot developers aiming for speed and efficiency in the development cycle.