Add header(copyright) information to existing source files

I want to add our company's copyright information to all of our EXISTING source code files.

The project is developed in Eclipse. so, for new files I can modify the settings as suggested here. But for existing files, how am I supposed to do this. How can I modify hundreds of java files to add the copyright information. (And I'm unable to open the releng plugin mentioned in the above link.

Any windows based text maniputaion scripting language will also help.

Correcting Konstantin's solution:

find . -name \*.java -exec sh -c "mv '{}' tmp && cp copyright '{}' && cat tmp >> '{}' && rm tmp" \;

Problem was that && is being interpreted by the shell directly instead of being passed to find. Escaping them is no solution either, as the find exec does not understand them. So just give the whole command to some shell.