Protect jar file from unzip utility

Question

Hi
I have an application in .jar file and I don't want that the client
can extract or unzip and see the contents of my .jar file.But still the .jar file
could run by mouse double click or java -jar command.
Anyone can give me an idea how to do it.
Thanks...

Answer 1

If java can read it on your client's machine, the client can read it. There is no way to prevent this. Here's the general cycle:
int protectionMode = chooseProtectionMode();
boolean haveCustomers = true;
while (haveCustomers)
  switch (protectionMode)
    case OBFUSCATE: 
      //You can obfuscate your code to make it (marginally) harder to
      //reverse-engineer.  If your client is really interested in your
      //code, this won't keep them from figuring out what it does.
      break;
    case ENCRYPT:
      // You can encrypt most of your class files, and build a
      // decrypting classloader, and build a framework that calls
      // the decrypting classloader to get at the rest of the jar. 
      // Of course, your client can just arrange to call your
      // classloader from their own, and write the (decrypted)
      // classfiles to disk, and then reverse engineer them.
      protectionMode = OBFUSCATE;
      break;
    case STATECHECK:
      // You can put some kind of check in your decrypting classloader
      // that calls System.exit() if it discovers it's being called in
      // such an unfriendly way.  Your client will take about 10 minutes
      // to find and remove the check.
      protectionMode = ENCRYPT;
      break;
    case REMOTE:
      // You can keep your code on your server and let the client run
      // something that talks to it.  The client will complain
      // vociferously, and refuse to use your app. 
      haveCustomers = false;
      break;
    default:
      // You can decide to stop stressing over something you can't
      // help, and write code that people will buy
  }(Sorry - in an odd mood, seen this question or one like it too often recently, not enough sleep...)