Ok, I've been doing some research into this and I'll be updating this answer according to my findings:
I've been using release-5.4.2 but I found that starting on release-5.4.2-HF07 they backported "org.nuxeo.runtime.tomcat.dev.NuxeoDevWebappClassLoader".
You can read some details in the NXP-7389
Basically to enable hot reload you should modify the conf/Catalina/localhost/nuxeo.xml l context configuration file and replace:
<Loader className="org.nuxeo.runtime.tomcat.NuxeoWebappLoader"
loaderClass="org.nuxeo.runtime.tomcat.NuxeoWebappClassLoader" />
by
<Loader className="org.nuxeo.runtime.tomcat.NuxeoWebappLoader"
loaderClass="org.nuxeo.runtime.tomcat.dev.NuxeoDevWebappClassLoader" />
Then you will be able to reload jars or bundles that ARE NOT in nxserver/bundles or nxserver/lib by specifyin the list of these bundles in the file nxserver/dev.bundles.
The format of this file is one file path per line (the file corresponding to the bundle JAR or directory).
Thus, you can point to project bin directories in your Eclipse IDE, or on JARs outside nuxeo server.
To specify a third party JAR that is not a BUNDLE you must prepend its path with a !.
YOu can use blank lines or lines starting with # for comments.
Example:
/path/to/may/project1/bin
/path/to/may/project2/bin
!/path/to/may/thirdparty.jar
...
Please notice that if you're using the 5.4 branch according to NXP-7629 the automatic hot-reloading (which checks dev bundles every 2 seconds) was disabled by default. To re-activate, just edit the launcher.properties template file and set the timer property org.nuxeo.app.installReloadTimer to true. A JMX a bean is exposed for controlling the reset instead.
If you ant to use ant to update the dev.bundles file, you can use something like this:
<target name="hotreload">
<condition property="file.matches">
<resourcecontains resource="${nxserver.dir}/dev.bundles" substring="${basedir}/target/classes" />
</condition>
<antcall target="update-dev-bundles"/>
<antcall target="touch-dev-bundles"/>
</target>
<target name="update-dev-bundles" unless="file.matches">
<echo message="Adding ${basedir}/target/classes to dev.bundles"/>
<echo file="${nxserver.dir}/dev.bundles" append="true"
message="${basedir}/target/classes"/>
</target>
<target name="touch-dev-bundles">
<touch file="${nxserver.dir}/dev.bundles"/>
</target>
