KeyStore Explorer is a free GUI replacement for the Java command-line utilities keytool, jarsigner and jadtool.
As far as Java keystore tools go, this is definitely the one with the most features, a friendly UI, and just feels like a real professional application..Believe me, I have tried a lot, and most have terrible UIs (IKeyman anyone?) I use it almost daily in working with keystores (not just JKS by the way) and it is a great help. Especially for those of us that want to avoid looking up obscure keytool/openssl options every time we just want to do simple operations on a keystore, or just find what it contains. The option in 5.0 to import a certificate directly from a SSL port is a real time-saver. I am very happy to see KSE on Sourceforge.