We can't live without Javadoc, but even if it useful, it's not complete. One missing thing is UML within the Javadoc.
To add UML to your Javadoc, is quite simple. You need to add Graphviz into your maven build.
First you need to download and install Graphviz. Go there Graphviz
After that you should add the variable GRAPHVIZ_HOME (that point to the installation folder) into your system.