Dynamic Downloading
Take a deep breath. Now we're ready to tackle dynamic downloading.
- Dynamic downloading allows us to put the _Stub class in a download directory on the server, instead of copying it to each client that wants to use it.
- Then, the client can download the stub dynamically.
- Any time you update the server and update the stub, you can count on the client grabbing the stub from the download directory. This saves you from sending a manual update to all of your users!
- A few steps I took:
- I created a download directory under /webapps/ROOT/ in Tomcat. The book said to create one under /webapps/, but I eventually found that it wanted one under /webapps/ROOT/.
- I placed ChatImpl_Stub.class and Chat.class in this directory.
- I added the argument -Djava.rmi.server.codebase=http://localhost:8080/download/ to the list of arguments I passed the server on startup.
- I removed the ChatImpl_Stub.class from the client directory to make sure it downloaded it dynamically.
- It didn't work. So I pulled my hair out for a while and tried a number of things. Then I thought that, since it is looking for chat.ChatImpl_Stub.class, perhaps I need to put the class files in a subdirectory of download called chat. I did that, and sure enough it works.
- Got it working, so now I can go back and fix my policy files. I took away AllPermission when I had it working, and tweaked the files until I came up with this:
- server.policy:
- client.policy:
I modified the policy files. Ok, I cheated and gave both AllPermission because I was tired, but certainly you can restrict permission better than this.
grant {
permission java.net.SocketPermission "*:1024-65535", "accept,connect,listen,resolve";
permission java.net.SocketPermission "*:80", "accept,connect,listen,resolve";
permission java.net.SocketPermission "*:8080", "accept,connect,listen,resolve";
};
grant {
permission java.net.SocketPermission "*:1024-65535", "connect";
permission java.net.SocketPermission "*:80", "connect";
permission java.net.SocketPermission "*:8080", "connect";
};