How do you enable hot swapping in a Spring Boot application?

Tale of Contents

Introduction

Hot swapping is a powerful feature in Java development that allows you to change your code and see the effects immediately, without restarting the application. In a Spring Boot application, enabling hot swapping enhances your development efficiency by minimizing downtime. This guide outlines the steps to enable hot swapping using Spring Boot DevTools.

Steps to Enable Hot Swapping

1. Add Spring Boot DevTools Dependency

To utilize hot swapping, you need to include the Spring Boot DevTools in your project. This can be done by adding the dependency to your pom.xml file if you are using Maven:

For Gradle users, add the following line to your build.gradle file:

2. Enable Automatic Build in Your IDE

For hot swapping to work seamlessly, your Integrated Development Environment (IDE) must automatically compile changes. Here’s how to set this up in popular IDEs:

• IntelliJ IDEA:
  • Go to File > Settings (or Preferences on macOS).
  • Navigate to Build, Execution, Deployment > Compiler.
  • Check the box for "Build project automatically."
  • Enable "Allow auto-make to start even if developed application is currently running" under the Advanced Settings section.
• Eclipse:
  • Go to Window > Preferences.
  • Expand the General section and select Workspace.
  • Check the box for "Build automatically."

3. Use the Right ClassLoader

Spring Boot DevTools uses a special class loader to manage application classes, allowing for the hot swapping of modified classes. When changes are made to your code, the DevTools class loader will automatically load the updated classes without restarting the entire application.

Practical Example

Running Your Application

After setting up the DevTools dependency and configuring your IDE, run your Spring Boot application as you normally would. Now, when you modify a Java class and save the changes, DevTools will automatically detect these changes and reload the modified classes.

Example: If you have a simple REST controller and you change the response message, upon saving the file, you’ll see the updated response immediately when you make a request to that endpoint.

Conclusion

Enabling hot swapping in a Spring Boot application using Spring Boot DevTools significantly enhances your development experience. By adding the DevTools dependency, configuring your IDE for automatic builds, and leveraging the special class loader, you can make real-time code changes without the need for full application restarts. This capability not only saves time but also streamlines your workflow, allowing you to focus on building and refining your application.