Note to developers:
This is a very brief overview.
There is more infomation on the JMeter Wiki.
Building Add-Ons
There is no need to build JMeter if you just want to build an add-on.
Just download the binary archive and add the jars to the classpath.
You may want to also download the source so it can be used by the IDE.
See the extras/addons* files in the source tree for some suggestions
Building JMeter
Acquiring the source
The source is distributed alongside the binary, or it can be downloaded from SVN.
The source archive and SVN do not contain any of the required library files.
You can download these by running the Ant command:
ant download_jars
Or you can download the binary archive for a release and unpack it into the same directory structure as the source.
This will ensure that the lib/ directory contains all the required jar files.
Compiling and packaging JMeter using Ant
JMeter can be built entirely using Ant; see build.xml for the targets that can be used.
Compiling and packaging JMeter using Eclipse
Once you have downloaded the source from SVN or the release archives, you can configure Eclipse.
The easiest way to do this is to replace the Eclipse .classpath file with the eclipse.classpath file provided with JMeter.
This will set up the source-paths and most of the libraries.
See also the file eclipse.readme.