Well, I searched all over the internet, but I didn't find even one resource on how to watermark java classes.
The idea is, to watermark a java class with some information such as a username. If the user circulates the java class, the watermark would make the oroginal user easily identifiable.
Or is there another way of doing this without watermarking?
I'd shy away from the term "watermarking", as that's more for images or sound. Anything that can compromise on quality by adding "noise".
The java class file does allow for custom / developer defined attributes, which can be stored in a class file.
The Java virtual machine specification dictates that if a VM does not recognise a an attribute, it must ignore it.
So, you would not be compromising the class file, it would be 100% valid and run on all VM's.
http://java.sun.com/docs/books/jvms/second_edition/html/ClassFile.doc.html#43817
However, if someone decompiled and recompiled your class, the attibute would be stripped out / not included.
Depends how strict you want to get, taking into account reverse engineering / decompilation.
regards,
Owen
It's probably overkill for what you want.
Simpler approaches might be
a) put your classes in a digitially signed jar file.
b) create a checksum ( CRC32 ) of each classfile.
Store these checksums "somewhere", and compare the class to the
checksum at runtime.
c) Only allow classes to be downloaded via http from a web server.
Would require a webserver, eg. apache.
Then your classpath would be something like
-classpath http:\\myserver\myapp\jar1.jar
