To deliver signed applications, one usualy needs to generate a keystore.
One can use the keytool command line program delivered as part of the SDK. Another way to create the keystore is to use the keytool maven plugin.
Cf the keytool maven plugin documentation.
One can make the webstart plugin generate a new keystore at each build. This can be convenient for demos and other less production critical projects (where signing needs to be done appropriately).