Hello all,
I wanted to share my experiences with running web applications with
m2e-wtp and Webby combined with JRebel [1]
JRebel is a tool that enhances JVM Hot Swap mechanism, so that most
changes can be applied dynamically to classes already loaded in
memory.
It aims to fix the very common problem in J2EE application
development - unacceptably long time between introducing a change in
the code and seeing the result in a running application.
It is a commercial tool, but the price is reasonable and free
licenses for OSS projects are available.
JRebel is available both as a standalone application that plugs into
JVM using javaagent mechanism, and as pulgins for Eclipse, IDEA and
NetBeans.
First, I've tried m2e-wtp + JRebel Eclipse plugin. The installation
went smoothly, and I was able to enable JRebel agent for the Tomcat
server that I used as the target for m2e-wtp assembled webapp.
I've run into a minor problem - disabling automatic publishing from
WTP server UI did not work, I had to edit server.xml by hand. This
is probably not related to neither m2e-wtp nor JRebel.
The application startup was considerably slower than without JRebel
- I expected that because classes had to be instrumented. Reloading
changes in the code worked as advertised, however build times after
changing a single Java source file were very noticeable - about 5s.
This certainly depends on the speed of the machine and size of the
application, so your mileage may vary.
Then I decided to try JRebel with Webby. I've uninstalled m2e-wtp
(and most WTP also) and installed Webby. Of course Webby run
configuration editor does not have JRebel tab, but I'm sure one
could be added as an optional extension if there's interest from the
community.
Fortunately standalone JRebel can be plugged in very easily. In the
JRE / VM arguments for a Webby launch configuration, I've added the
following:
-javaagent:${env_var:JREBEL_HOME}/jrebel.jar
-Dworkspace.root=${workspace_loc}
This way I could share the configuration with other people on my
team. workspace.root system property is used in rebel.xml
configuration file, that specifies the filesystem location of the
classes that need to be monitored and reloaded on demand by JRebel.
I've placed this file in src/main/resources folder in my top level
webapp module and it looks like this:
<?xml version="1.0" encoding="UTF-8"?>
<application
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://www.zeroturnaround.com"
xsi:schemaLocation="http://www.zeroturnaround.com
http://www.zeroturnaround.com/alderaan/rebel-2_0.xsd">
<classpath>
<dir
name="${workspace.root}/coral-api/target/classes"/>
<dir
name="${workspace.root}/coral-browser/target/classes"/>
...
</classpath>
</application>
I am not using any <web> tags, because Webby
takes care of providing the J2EE container with up to date resource
files.
With this configuration I was able to achieve reasonable startup
time - Webby is really much faster than WTP, and also excellent
build times - below 1s. Everything worked very smoothly. I was able
to code and see the results with barely any latency at all! Compared
to m2e 0.12 + WTP the boost is incredible :)
cheers,
Rafał
[1]
http://www.zeroturnaround.com/jrebel/
