Code reloading shortens the edit–check loop in a Quarkus application. In Dev mode, save a change and send an HTTP request, such as by refreshing a browser page. Quarkus recompiles and reloads the application in the background, then serves the request using the changed version. There is no need to manually package, restart, or launch a new JVM for each edit. section 2.3 section 3.1
To try the loop:
- Start Dev mode with `./mvnw quarkus:dev`, `./gradlew --console=plain quarkusDev`, or `quarkus dev`, according to your tooling. section 2.3
- Change a Java REST resource, save it, and refresh its browser page. You can also press `s` in the Dev mode terminal to trigger a reload without sending a request. section 3.1.1
- Change an HTML resource or `application.properties` in the same way. Changes to `pom.xml` or `build.gradle`, including a new dependency, can also trigger a reload. section 3.1.2
A detected change does not reload immediately: Quarkus waits for a request or a manual trigger, holds the request while reloading, and then responds. Reloads normally take a few hundred milliseconds, though work such as downloading a new dependency can take longer. The process reuses the JVM through a class-loader architecture; its internals are beyond this practical workflow. section 3.1.2
Change a greeting, then break it
Change the string returned by a REST greeting method and refresh to see the new response. Dev mode logs the stop and reload time. If you instead remove the return statement’s semicolon, the next request produces an HTTP 500 error page with compilation details; Dev mode remains running so you can correct the code and try again. section 3.1.1 section 3.7
A full reload discards application state: classes are loaded again in a new class loader, and the old objects are released. For some minor changes, instrumentation-based reload can preserve affected objects by replacing bytecode instead; enable it with `quarkus.live-reload.instrumentation=true` in `application.properties` or press `i` in the terminal or Dev UI. Extensions that hold connections or files may need shutdown hooks to clean them up during hot reload. This is a development workflow, not a substitute for packaging and running the production application. section 3.1.2 section 12.1.5 section 2.3
