title: How to generate a checksum for jar file
body: <p>We want to implement a feature like this: when user firstly run the app, app will download a jar file to local PC from a server and load the jar file but when user run the app again, app can distinguish if the content of the jar file in local folder is same as the one on server, if so not download it again just load it from local folder; if not app will download it and update local one (the jar file name on server and on local must be same). Currently one solution I can think out is to use checksum that is app generates the checksum of local jar file then get the checksum of server jar file from the server, check if they are same, if so not download again, if not download and update. Is there a simple way to generate checksum of a jar file? Or is there any other better solution for this feature? Thanks. </p>