Using JRebel on a web app can really boost your edit code <-> reload
browser response cycle. Basically it allows classes to be reloaded in
the JVM in place. Its great when hacking, say, Lift apps; you can run
your application like this in maven...
export MAVEN_OPTS="-noverify -javaagent:$JAVAREBEL_HOME/javarebel.jar"
mvn jetty:run
where JAVAREBEL_HOME points to where you installed the jrebel jar -
you can download it here:
http://www.zeroturnaround.com/blog/free-javarebel-for-scala-users-zeroturnaround-announces/
Then in another shell you can run
mvn scala:cc
Then as you write or edit Scala classes in your IDE/editor, the
"scala:cc" incrementally compiles them to classes. Then the JRebel
ninja stuff automatically reloads the classes inside the JVM. What
this means is that you can hack Lift controllers and snippets of code
- and just hit reload in your browser within about a second of the
time you've finished editing and hey presto, you get to test your new
code. No need to stop/start your web container etc. Very Railsish
The above should work just as well with Glassfish too - or indeed any
servlet container.
This works great for things like Lift; however there's currently a bit
of an issue for folks hacking Jersey apps; namely that adding a new
Jersey controller - or updating a controller to add/remove/change the
URI mappings; does not cause the re-loading of the Jersey URI mapping
stuff - since right now (naturally) that just happens once on startup.
All that is required really is a JRebel plugin for Jersey; which
basically is a little listener to the JRebel events (such as when a
class has been reloaded) which can then be used as a hook to
re-initialise the Jersey filter/servlet to detect changes in the JAXRS
mappings.
This certainly isn't a show stopper or anything; its just a velocity
thing; if folks could add new Scala/Java controllers on the fly
without restarting their web app (whether Jetty, Glassfish, Tomcat,
whatever) it'd help folks feel more RAD in a Railsy kinda way.
I've raised an issue to track this so we don't forget about it.
https://jersey.dev.java.net/issues/show_bug.cgi?id=486
BTW this issue came up on the JRebel forum too
http://www.zeroturnaround.com/forum/topic.php?id=330#post-1379
here's a little article that shows how to implement a JRebel plugin...
http://code.google.com/p/zt-oss/wiki/SimpleJavaRebelPlugin
so basically if we had a little Jersey-JRebel plugin, folks could use
it when they run their app inside Jersey/Tomcat/Glassfish, which would
just listen for JRebel events that a class has been reloaded and
decide if it might be a resource or not (e.g. has it any JAXRS
annotations or is it a type currently used in the JAXRS URI space) and
if so, reload the jersey filter/servlet stuff.
Here's the SDK javadoc...
http://www.zeroturnaround.com/docs/javarebel-sdk/javadoc/
e.g. here's how to add a listener to be notified when a class was reloaded...
http://www.zeroturnaround.com/docs/javarebel-sdk/javadoc/org/zeroturnaround/javarebel/Reloader.html
--
James
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