I have the binary version of a project containing Java Class Files, Applets and Jars and I want to reverse all this files to its orginal source code in order to be apple to develope this code. is that possible? How can I do that? which tools?

There are many Java decompilers/disassemblers such as JAD, DeCafe, NMI's Java decompiler, IDA etc. Most of them really work.
Just do a google search, you will find them. *.JAR can be decompressed with WinRAR.
And you can find some java reversing essays from http://www.woodmann.net/fravia/what_new.htm.

good luck.