What is Spring Boot DevTools?

Spring Boot DevTools is a developer productivity tool provided by Spring Boot. It helps developers build, test, and debug Spring Boot applications faster by automatically restarting the application, refreshing browser content, disabling template caching during development, and improving the overall development workflow.

In simple words, Spring Boot DevTools reduces the time developers spend manually restarting the application after every code change. It is mainly used during development and should not be used in production environments.

Why is Spring Boot DevTools Used?

During Spring Boot application development, developers frequently modify Java classes, controllers, services, configuration files, HTML templates, CSS files, and JavaScript files. Without DevTools, every major backend change may require a manual application restart. This slows down development.

Spring Boot DevTools solves this problem by providing automatic restart and live reload support. It improves developer efficiency and helps teams build applications faster.

Key Features of Spring Boot DevTools

1. Automatic Application Restart

One of the most useful features of DevTools is automatic restart. When a developer changes Java code or application configuration, DevTools detects the change and restarts the application automatically.

This is faster than manually stopping and starting the application because DevTools uses two classloaders internally. One classloader loads application code that changes frequently, and another loads libraries that usually do not change. Because only the application part is reloaded, restart becomes faster.

2. LiveReload Support

Spring Boot DevTools supports LiveReload. When static resources such as HTML, CSS, or JavaScript files are changed, the browser can automatically refresh and show the latest changes.

To use this feature, developers may need to install a LiveReload browser extension. This is useful for frontend development when working with Thymeleaf pages, static HTML pages, CSS styling, and JavaScript behavior.

3. Disables Template Caching

In production, template engines such as Thymeleaf usually cache templates for better performance. But during development, caching can be a problem because changes may not appear immediately.

DevTools automatically disables caching for supported template engines during development. This allows developers to update templates and immediately see the result without clearing cache manually.

4. Development-Friendly Default Properties

Spring Boot DevTools automatically applies some development-friendly settings. For example, it disables certain caches and enables features that make debugging easier.

These defaults are useful only during development. In production, caching and optimized settings are important for performance and security.

5. Remote Development Support

Spring Boot DevTools also provides remote development support, but this feature should be used very carefully. Remote DevTools can allow code updates on a remote application during development.

For security reasons, remote DevTools should never be enabled on a public production server.

How to Add Spring Boot DevTools

To use DevTools in a Maven-based Spring Boot project, add the following dependency in the pom.xml file:

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

The optional value is usually set to true because DevTools is intended only for development. It should not be packaged as a required dependency for other projects.

Gradle Dependency for Spring Boot DevTools

If the project uses Gradle, DevTools can be added like this:

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

Example: Without DevTools vs With DevTools

Without DevTools

Developer changes controller or service code.
Developer manually stops the Spring Boot application.
Developer starts the application again.
Developer opens the browser and tests the change.

With DevTools

Developer changes controller or service code.
DevTools detects the change automatically.
Application restarts automatically.
Developer refreshes or checks the browser quickly.

Real-Time Example

Suppose you are building an online learning platform using Spring Boot and Thymeleaf. You have a controller that displays course details:

@Controller
public class CourseController {

    @GetMapping("/courses")
    public String courses(Model model) {
        model.addAttribute("message", "Welcome to Spring Boot Courses");
        return "courses";
    }
}

If you change the message from:

Welcome to Spring Boot Courses

to:

Learn Spring Boot with Real-Time Projects

DevTools automatically restarts the application after the code change. You do not need to stop and start the server manually.

Important Properties of Spring Boot DevTools

DevTools behavior can be customized using application.properties.

spring.devtools.restart.enabled=true
spring.devtools.livereload.enabled=true
spring.thymeleaf.cache=false

Disable Restart

If you want to disable automatic restart, use:

spring.devtools.restart.enabled=false

Exclude Specific Files from Restart

Sometimes developers do not want the application to restart for certain file changes. For example:

spring.devtools.restart.exclude=static/**,public/**

This means changes inside static and public folders will not trigger a full application restart.

Does DevTools Work in Production?

Spring Boot DevTools is designed for development only. It is automatically disabled when the application is packaged and run as a fully executable JAR in production.

DevTools should not be used in production because production applications need stable performance, proper caching, security, and controlled deployment processes.

Advantages of Spring Boot DevTools

Reduces manual restart time during development.
Improves developer productivity.
Automatically refreshes application changes.
Disables template caching during development.
Makes debugging and testing faster.
Works well with Spring MVC, Thymeleaf, REST APIs, and microservices development.

Limitations of Spring Boot DevTools

It is not meant for production use.
Some changes may still require a full manual restart.
LiveReload may need a browser extension.
It may not work perfectly with all IDE configurations unless build settings are correct.
Remote DevTools can be risky if enabled without proper security.

Spring Boot DevTools Interview Explanation

In interviews, Spring Boot DevTools can be explained as a development-time tool that improves productivity by automatically restarting the application when code changes are detected. It also supports LiveReload, disables caching for templates, and provides development-friendly configurations.

A good interview answer should also mention that DevTools should not be used in production. Its main purpose is to make local development faster and more convenient.

Difference Between DevTools Restart and Server Restart

Feature	DevTools Restart	Manual Server Restart
Speed	Faster	Slower
Effort	Automatic	Manual
Use Case	Development	Development and production
Class Loading	Uses restart classloader	Reloads complete application

Best Practices for Using Spring Boot DevTools

Use DevTools only in local development environments.
Do not enable remote DevTools in production.
Keep the dependency optional in Maven projects.
Disable template caching during development for faster UI changes.
Use IDE auto-build settings to make DevTools restart work properly.
Do not depend on DevTools for production deployment or hot fixes.

Common Issue: DevTools Not Restarting Automatically

If DevTools is not restarting the application automatically, check the following:

Make sure the DevTools dependency is added correctly.
Enable automatic build in your IDE.
Check whether restart is disabled in application.properties.
Verify that the changed files are not excluded from restart.
Restart the IDE if DevTools is not detecting changes.

Conclusion

Spring Boot DevTools is a useful development tool that helps developers work faster with Spring Boot applications. It provides automatic restart, LiveReload support, cache disabling, and development-friendly settings. It is especially helpful when building REST APIs, web applications, microservices, and Thymeleaf-based projects.

However, DevTools should be used only during development and not in production. For production environments, applications should be properly built, tested, optimized, and deployed using a controlled deployment process.

Frequently Asked Questions