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Application hot reload with spring-boot-devtools and the LiveReload browser plugin

GIVEN

You've installed the LiveReload-Plugin in your browser, and an IDE like IntelliJ IDEA.

WHEN

You set the spring.devtools.remote.secret property in the application.properties file,

Like any important password or secret, the value should be unique and strong such that it cannot be guessed or brute-forced.

You run Application.java from your IDE,

You visit http://localhost:8080/hello,

You click on the plugin icon in your browser to enable LiveReload,

You change something in the HelloController or do anything else in src/main/java,

You press Build → Build Project / STRG + F9 in IntelliJ IDEA,

THEN

The application should restart automatically.

Your browser should automatically refresh the site

You can also run your application as a JAR or as a Docker container.

SECURITY WARNING:

Remote support is opt-in as enabling it can be a security risk. It should only be enabled when running on a trusted network or when secured with SSL. If neither of these options is available to you, you should not use DevTools' remote support. You should never enable support on a production deployment.

GIVEN

You have selected Run → Edit Configurations... in IntelliJ IDEA and added a new configuration with type Application:

Name: RemoteSpringApplication
Main class: org.springframework.boot.devtools.RemoteSpringApplication
Program arguments: http://localhost:8080 (or whatever your remote URL is)

WHEN

You use build.sh or build.cmd regarding of your operating system to build and run the application outside your IDE,

Usage: build [{jar}|docker] [{dev}|prod]

Build the application as jar or docker container and run it in development or production mode.

You press Run → RemoteSpringApplication / SHIFT + F10 in IntelliJ to run the configuration.

You visit http://localhost:8080/hello again,

You do anything in src/main/java,

You press Build → Build Project / STRG + F9 in IntelliJ IDEA,

THEN

You'll see something like this in the RemoteSpringApplication execution log:

[...] ClassPathChangeUploader  : Uploaded 1 class resource
[...] DelayedLiveReloadTrigger : Remote server has changed, triggering LiveReload

The application should restart automatically, and your browser should automatically refresh the site.

Hint:

DevTools are disabled in "production" mode. To see how this happens, explore the build block in build.sh / build.cmd. It's an override of the maven property exclude.devtools specified and used in the pom.xml.

To trigger an application restart and browser refresh you have two other options instead of press Build → Build Project / STRG + F9 in IntelliJ IDEA.

  • You can recompile only a specific class in IntelliJ IDEA: To do this, press Build → Recompile '*.java' / STRG + SHIFT + F9.

Also, you can activate 'Build project automatically' in IntelliJ IDEA to let the IDE build changed classes automatically:

  • Press Help → Find Action... / CTRL + SHIFT + A in IntelliJ IDEA, search for Build project automatically and enable it.

  • Press Help → Find Action... / CTRL + SHIFT + A in IntelliJ, search for Registry... and enable compiler.automake.allow.when.app.running.

Now when you press File → Safe All / STRG + S in IntelliJ to save all, IntelliJ should automatically build - only the changed files.

You can change the spring.devtools.restart.poll-interval and spring.devtools.restart.quiet-period properties in application.properties to change the behaviour on slow machines. More information about these properties you can find in the documentation of Spring Boot.