What is the significance of the spring.devtools.restart.enabled property?

Table of Contents

• Introduction
  • What Does spring.devtools.restart.enabled Do?
  • Default Behavior
  • How to Configure spring.devtools.restart.enabled
    • In application.properties:
    • In application.yml:
  • When to Disable Automatic Restarts
  • Practical Example of spring.devtools.restart.enabled
    • Example 1: Enabling Automatic Restarts for Development
    • Example 2: Disabling Automatic Restarts for Performance Optimization
    • Example 3: Using DevTools with Remote Debugging
  • Other Properties Related to Restart
    • 1. spring.devtools.restart.exclude
    • 2. spring.devtools.restart.poll-interval
• Conclusion

Introduction

In Spring Boot DevTools, the spring.devtools.restart.enabled property plays a crucial role in managing whether the automatic restart feature is enabled or disabled. Automatic restarts are a major feature of Spring Boot DevTools, allowing your application to detect changes in the code or resources and automatically restart, thus improving the developer experience by avoiding the need for manual restarts.

This property, when configured, controls the behavior of the restart mechanism in Spring Boot applications, making it an essential configuration for streamlining development workflows.

In this guide, we will discuss the significance of the spring.devtools.restart.enabled property, how to configure it, and when to use it.

What Does spring.devtools.restart.enabled Do?

The spring.devtools.restart.enabled property is used to enable or disable the automatic restart feature of Spring Boot DevTools. By default, automatic restarts are enabled when you add the Spring Boot DevTools dependency to your project, but this property allows you to control the behavior of this feature.

Setting spring.devtools.restart.enabled to true allows DevTools to restart the application automatically when changes to the code or resources are detected. Setting it to false will disable the automatic restart feature, which could be useful in certain situations, such as for performance optimization or when you want more control over restarts.

Default Behavior

By default, Spring Boot DevTools automatically restarts the application when any change is made to the classpath (e.g., modifying Java files or updating resources). This is achieved by monitoring the src/main/java and src/main/resources directories. The restart feature is designed to help developers see the impact of code changes instantly without needing to restart the application manually.

How to Configure spring.devtools.restart.enabled

To control the automatic restart feature, you can configure the spring.devtools.restart.enabled property in your application's application.properties or application.yml file.

In application.properties:

Or to disable it:

In application.yml:

Or to disable it:

When to Disable Automatic Restarts

While automatic restarts are convenient during development, there are cases when you might want to disable this feature:

1. Performance Considerations: If you're working in a large project with numerous classes and resources, the restart mechanism can sometimes add overhead. In such cases, you might prefer to disable it temporarily and manage restarts manually to reduce resource consumption.
2. Remote Debugging: In some scenarios, such as remote debugging, automatic restarts might interfere with debugging sessions. Disabling restarts ensures that the application remains in the same state during the debugging process.
3. Continuous Integration / Deployment: In CI/CD pipelines, automatic restarts could disrupt the flow of your build or testing process. Disabling restarts in these environments ensures that the application only restarts when explicitly configured in the deployment pipeline.
4. Memory Management: For memory-sensitive applications, disabling automatic restarts may help manage memory consumption, particularly if restarts lead to increased load on the JVM.

Practical Example of spring.devtools.restart.enabled

Example 1: Enabling Automatic Restarts for Development

In most development environments, you will want the application to restart automatically when changes are made to the code. The default behavior works for most cases, but you can explicitly enable it as shown below:

With this configuration, any change you make to Java files, resources, or configurations in the src/main directory will automatically trigger a restart of the application. You can continue developing without manually restarting the server each time you make a change.

Example 2: Disabling Automatic Restarts for Performance Optimization

If your project is large and the automatic restarts cause performance issues, you might want to disable the feature temporarily. You can do this by setting spring.devtools.restart.enabled to false.

In this case, you will need to manually restart the application when you make changes to the code or resources. This could be a preferred option for long-running tests or resource-intensive operations.

Example 3: Using DevTools with Remote Debugging

When debugging remotely, automatic restarts can disrupt the session. To avoid this, you can disable the automatic restart feature:

This ensures that the application doesn't restart automatically, allowing you to keep the same application state during remote debugging and focus on stepping through the code.

Other Properties Related to Restart

In addition to the spring.devtools.restart.enabled property, there are several other properties related to the restart mechanism in Spring Boot DevTools. Some of these properties help fine-tune the restart behavior.

1. spring.devtools.restart.exclude

This property allows you to exclude certain directories or files from triggering a restart. For example:

In this case, changes in the static or public directories will not trigger a restart, which can help improve performance when working with large static assets like images or stylesheets.

2. spring.devtools.restart.poll-interval

This property controls the interval (in milliseconds) at which DevTools checks for file changes to trigger restarts. The default is 1000 milliseconds (1 second). You can adjust it if you need a faster or slower polling interval:

This would reduce the time between change detection checks to 500 milliseconds.

Conclusion

The spring.devtools.restart.enabled property is essential for controlling whether automatic restarts are enabled or disabled in a Spring Boot application. This feature enhances the development experience by automatically restarting the application when code or resource changes are made, allowing developers to see changes immediately without manual restarts.

However, in certain situations—such as for performance optimization, remote debugging, or CI/CD environments—you may choose to disable the automatic restart feature. This is easily configurable via the spring.devtools.restart.enabled property in the application.properties or application.yml file.

By configuring this property according to your needs, you can improve your development workflow and streamline the process of building and testing Spring Boot applications.