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Frontend watch

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The frontend watch rebuilds your src/main/frontend sources while the app runs and refreshes the browser, so a frontend change shows up without a manual build or a server restart. It's the development side of the frontend bundler.

Running the watch​

Run it alongside your server, as the goal before the one that starts the app. A Spring project sets this as its default goal, so mvn with no arguments starts both:

mvn compile webforj:watch spring-boot:run

Against the Maven Jetty plugin, start it the same way:

mvn compile webforj:watch jetty:run

For the watch as a build step, see Build and tests.

What happens on a change​

When you save a source, the watch rebuilds and sends the changed files to the browser. What the browser does depends on the output, not the source you edited:

  • A stylesheet patches in place, with no reload, so form data and scroll position stay. A .css, .scss, .sass, or .less edit lands here.
  • An image swaps in place, with no reload.
  • Anything else reloads the view. A .ts, .tsx, or .js edit lands here, since new behavior needs a fresh page.

If a rebuild touches several files and all can patch in place, the browser stays put. If even one can't, it reloads, so you never see a change land halfway.

Across a server restart​

A Java change restarts the server, through Spring DevTools, the Maven Jetty plugin, or JRebel. The watch keeps the frontend in step with it:

  • Your styles stay applied across the restart, instead of flashing unstyled.
  • The page reloads once the app is ready, not before, so you don't hit an error from reloading too early. A small indicator shows while the server restarts; a manual reload shows nothing.
  • Adding or removing a @BundleEntry takes effect on the next restart.

Configuration​

Live reload is a webforJ setting, so it applies whichever server you run. A Spring app reads these keys from application.properties; a standalone server, such as the Maven Jetty plugin, reads the same keys from webforj.conf.

application.properties
# Refresh the browser on a change
webforj.devtools.livereload.enabled=true

# Patch stylesheets and images in place instead of reloading (default: true)
webforj.devtools.livereload.static-resources-enabled=true

# Port and path the browser connects on (defaults: 35730, /webforj-devtools-ws)
webforj.devtools.livereload.websocket-port=35730
webforj.devtools.livereload.websocket-path=/webforj-devtools-ws

# Heartbeat interval in milliseconds (default: 30000)
webforj.devtools.livereload.heartbeat-interval=30000