I find myself needing to generate a checksum for a string of data, for consistency purposes. The broad idea is that the client can regenerate the checksum based on the payl
CRC32 is not too hard to implement in any language, it is good enough to detect simple data corruption and when implemted in a good fashion, it is very fast. However you can also try Adler32, which is almost equally good as CRC32, but it's even easier to implement (and about equally fast).
Adler32 in the Wikipedia
CRC32 JavaScript implementation sample
Either of these two (or maybe even both) are available in Java right out of the box.