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Wouldn’t it be great if, when building a website, you could modify your code and immediately see the change reflected in your web browser? Great news, Kweb can do this!

Step 1 : Install Dynamic Code Evolution VM (DCEVM) Java patch

Go to and download the latest DCEVM light installer (DCEVM-light-8u112-installer.jar at the time of writing).

Run the installer by double-clicking on it.

Note for Mac users: You may get an error like “DCEVM-light-8u112-installer.jar” can’t be opened because it is to an unidentified developer, if so you should control-click the file and select “Open” to the drop-down menu, then click “Open”.

You must now select your Java Development Kit directory. If it isn’t already listed click Add installation directory, for example on a Mac it may be /Library/Java/JavaVirtualMachines/jdk1.7.0_121.jdk/Contents/Home.

Click Install DCEVM as altjvm.

When the installation is complete you can quit the DCEVM installer.

Step 2 : Download HotSwapAgent

Go here and download the latest hotswap-agent .jar, (hotswap-agent-1.1.0-SNAPSHOT.jar at the time of writing).

Save it somewhere appropriate, perhaps in a directory called javalibs in your home directory (it doesn’t really matter where you put it but you’ll need the full path and filename later).

Step 3 : Modify your project’s run configuration

In intelliJ select Edit Configurations... under the Run menu, and paste the following into the VM Options field:

-XXaltjvm="dcevm" -javaagent:PATH_TO/hotswap-agent.jar=disablePlugin=AnonymousClassPatch

Be sure to edit PATH_TO/hotswap-agent.jar to be the full path and name of the hotswap-agent .jar file you downloaded in Step 2.

Note that =disablePlugin=AnonymousClassPatch was necessary at the time of writing to prevent a non-fatal error, but this bug in HotSwapAgent has been reported and may be fixed by now.

Step 4 : Configure Kweb to refresh webpages automatically

Set the refreshPageOnHotswap Kweb constructor parameter to true:

    Kweb(port = 1234, refreshPageOnHotswap = true) {

Step 5 : Run your code

Now run your project in debug mode (the button to the green bug), you should see something like this:

HOTSWAP AGENT: 19:01:57.851 INFO (org.hotswap.agent.HotswapAgent) - Loading Hotswap agent {1.1.0-SNAPSHOT} - unlimited runtime class redefinition.
HOTSWAP AGENT: 19:01:58.178 INFO (org.hotswap.agent.config.PluginRegistry) - Discovered plugins: [KwebHotswapPlugin]
HOTSWAP AGENT: 19:01:59.145 INFO (org.hotswap.agent.config.PluginRegistry) - Discovered plugins: [Hotswapper, WatchResources, ClassInitPlugin, Hibernate, Hibernate3JPA, Hibernate3, Spring, Jersey1, Jersey2, Jetty, Tomcat, ZK, Logback, Log4j2, MyFaces, Mojarra, Seam, ELResolver, WildFlyELResolver, OsgiEquinox, Owb, Proxy, WebObjects, Weld, JBossModules, ResteasyRegistry, Deltaspike, JavaBeans]
HOTSWAP AGENT: 19:01:59.231 INFO (org.hotswap.agent.config.PluginRegistry) - Discovered plugins: []
HOTSWAP AGENT: 19:02:00.009 INFO (org.hotswap.agent.config.PluginRegistry) - Plugin 'org.hotswap.agent.plugin.logback.LogbackPlugin' initialized in ClassLoader 'sun.misc.Launcher$AppClassLoader@18b4aac2'.

This indicates that HotSwapAgent is working, and in particular look out for Discovered plugins: [KwebHotswapPlugin] as this will indicate that Kweb is aware of HotSwapAgent (this is necessary for the automatic refresh).

Step 6 : Try it!

Launch a web browser and point it at your Kweb instance. Now make a change to your code, and rebuild the file you’ve modified (Shift+Command+F9 on a Mac), in a few seconds the browser window should automatically refresh to reflect the change.

Note that HotSwapAgent doesn’t work to every code modification, for example if you make a change to the configuration of your Kweb object it will not pick this up.

Next: More examples »»