Load jar from URL

Question

I've been searching for days but I have not found a clear answer. How would I go about writing a small jar file to give to my users that simply gets a jar file from a URL (with multiple classes in it) and run it. It would be great if the end user never actually has the jar on his computer at anytime. I am doing this as a small security measure.

Answer 1

If the user is going to execute your code, it must exist on their computer. It's just the way it works.

If you wanted to re-write your code to perform most of the work on your servers, that'd be one mechanism to combat piracy, but it does mean that you need to duplicate all the input verification checks: perform them once on the client side, for reasonable response time, and again on your own servers, to ensure that your users aren't trying to use your services improperly.

Another mechanism would be to run a VNC server on your servers, and ask your users to VNC in. The software executes completely on your servers. It is a draconian step though, one your users will likely detest.

Answer 2

I am not sure how you'd go about it, but I know that using Maven allows you to access things without having the jar locally. You can just specify the URL. So maybe look into how they do their repositories.

Answer 3

Another option would be to encrypt your JAR file and write a custom class loader that decrypts it on the fly on client machines. This won't prevent a power user from attaching a debugger to the JVM and examining your byte code, but it prevents the typical user from having access to your code.