Graffiti is a core java based tool used to analyse jar files. It generates minimal bootstrap based html files with all the required statistics of the jar file. It is NOT a UML diagram generation tool.
Note : Please use the WebVersion link to upload jars containing .class files and not the source .java files
You can click on the Web Version button for a working demo. The same will allow you to upload a jar and will generate the output as a zip file available for download.