A Maven plugin for hot-deploy of Vert.x projects
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Hot reloading of Vert.x Verticles for Maven and Buck

Build Status Join the chat at https://gitter.im/dazraf/vertx-hot


  1. Background
  2. Aims
  3. Instructions
  4. Example Project
  5. Design Notes
  6. Contributors


Vert.x is an incredible toolkit for developing high-performance applications.

This plugin can speed up your dev cycle in popular build systems, such as Maven.

Write your code and see the changes auto reload into your JVM. Fully debuggable.

This plugin was originally written for personal use. Its shared here under the MIT licence.

Contributions most gratefully received and recognised.


  1. Detect source changes
  2. compile stale targets
  3. Hot Reload
  4. Full Debug without needing to attach to secondary processes
  5. Intuitive integration with Maven toolchain
  6. Fast at least much faster than using a manual workflow

Maven Instructions

Step 1: Download

Release versions of the Maven plugin are available in Maven Central. Snapshots are available in Sonatype. Zip'd releases are available here.

Please note: the latest version of the plugin depends on vert.x 3.1.0.

Step 2: Add to your project

Add the following to your project pom.xml:

        <verticleReference>class or service name</verticleReference>
        <configFile>config filename</configFile>

The configuration has the following elements:


  • verticleReference - either the fully-qualified reference to the top-level verticle of your application or a service reference.


  • configFile - the class path to the verticle configuration file. When loaded, vertx:hot will add the property "devmode": true.

  • liveHttpReload - when true, all web pages served by the application verticles will auto reload when any source is changed. default: true

  • buildResources - when set to true, any change to files under the resource directories will trigger a compile. Use this if your resources generate sources. default: false

  • notificationPort - websocket port for browser notifications. Used in conjunction with liveHttpReload: true. Default is 9999.

  • extraPaths - list of additional paths to be watched. This has a list of <extraPath> elements. Example as follows:

    <!-- default -->
    <!-- <action>Redeploy</action> -->

Step 3: Run it

You can run it either on the command line with:

mvn vertx:hot

Or, in your favourite IDE:

  • For any IDE you'll need a locally installed maven installation. Bundled / Embedded maven installations do not work.

  • IntelliJ IDEA:

    • Run - open the Maven side-bar, expand the Plugins/vertx section and double-click on vertx:hot goal. Any changes to your project's main source (e.g. src/main) will cause a hot deploy.
    • Debug - right-click on the vertx:hot goal and select Debug.
  • Eclipse:

    • Run - create maven build runner for vertx:hot goal. For Eclipse Mars on OS X, I found I had to set the JAVA_HOME environment variable in the runner. Once setup, Run it.
    • Debug - as above, but instead of Run, Debug

Step 4: Stopping the plugin

Press either: <Enter> or Ctrl-C.

Example Project

There are two simple test project under example1 and example2. The latter is an adaption of the excellent ToDo App by Scotch, with a vert.x reactive flavour.

To run either:

  1. You will need bower on your path.
  2. After running mvn clean install in the parent directory
  3. cd example1 or cd example2
  4. mvn vertx:hot
  5. Browse to http://localhost:8888
  6. Open up the project in your favourite IDE/Editor and try changing some code or static resources
  7. The browser will automatically reload. The IDE/shell console will show the unload | recompile | reload activity.

Buck Instructions

Buck is an efficient build system capable of identifying and recompiling only what it absolutely has to.

Before you rush off to switch from Maven/Gradle to Buck, it's important to bear in mind that Buck is not (and doesn't intend to be) as featureful as Maven. If you're used to transitive dependency retrieval, haven't heard of the concept of checking-in dependencies, leverage multitudinous Maven plugins, have developed custom Maven plugins, regularly rely on your build system's strong IDE integration, or just need things to work "out-of-the-box", then Buck might not be for you. However, if you are looking for outrageously fast builds, are prepared to rethink your project structure, and if the concepts behind Buck resonate for you, then you may want to give it a try.

The Buck support in vertx-hot is presently both limited and inefficient, but is hopefully sufficient to be of use to simple projects. As always, feature and pull requests are most welcome.

Step 1: Get the jar

The vertx-hot-buck build produces a fat-jar, to make inclusion from Buck projects fairly simple.

A few dependencies have been excluded, either due to shading complexities or to improve flexibility:

  • Vertx - likely already on your classpath. We build against 3.1.0, but more recent versions should be fine too.
  • SLF4J - the logging API. Drop in slf4j-api and your chosen implementation. We build against 1.7.12, but again this should be fairly flexible.
  • Buck - expected to reside on your PATH

If you're checking-in dependencies to your VCS, as per the recommended Buck methodology, then:

  1. Store the vertx-hot-buck jarfile in your lib directory
  2. Reference it using a prebuilt_jar rule:
  name = 'vertx-hot-buck',
  binary_jar = 'lib/vertx-hot-buck.jar'

If you fetch libraries from an m2 compatible repository, then you can include a corresponding remote_file rule to perform the fetch.

Step 2: Add to your project

An easy way to configure a buck hot deploy target is with a dedicated main class.

You'll likely want to configure the logger:

System.setProperty("vertx.logger-delegate-factory-class-name", "io.vertx.core.logging.SLF4JLogDelegateFactory");

Then configure your hot deployment:

  .withHotDeployConfig(new HotDeployParameters()

Executing the main method, with an appropriate classpath, will start the hot deployment.

The buck deployment parameters are:


  • withBuildTarget - The Buck build target to invoke when a filesystem change is detected.


  • withProjectRoot - a relative path to your project's root. Defaults to the present working directory.

  • withFetchMode - if you'll be updating remote_file rules that need fetching before each build, you can set a non-manual FetchMode. At present, this uses a crude & inefficient implementation.

The hot deployment configuration options are described in the Maven installation instructions.

Design Notes

sequence diagram


With many thanks: