Whatever... [Deepak Alur's Blog]: Deepak Alur's Blog @ Sun

It shouldn't be this wicked. Ok, I admit it has been a while since I implemented a Java RMI based client/server. But, it shouldn't be this wicked. So, I was trying to get some RMI client/server code running on my machine. And I kept getting was this friggin exception:

Caused by: javax.naming.CommunicationException [Root exception is java.rmi.ServerException: 
RemoteException occurred in server thread; 
nested exception is: java.rmi.UnmarshalException: error unmarshalling arguments; 
nested exception is: java.lang.ClassNotFoundException: com.sun.salsa.PatternModelImpl_Stub

The RMI docs said that anytime you get a ClassNotFoundException, it is most likely caused by an improperly set codebase^[J] So I checked the value of my java.rmi.server.CodeBase property. It was set as follows:

java.rmi.server.CodeBase=file://dev/salsa/classes 

I checked to make sure that the directory was there and that all the stubs and other classes were in there. They were. So, I ran the RMI server program again. But, again I got the same exception. What the heck is going on? And then it hit me. Isn't that supposed to be codebase and not CodeBase?

So I change "CodeBase" to "codebase" and reset the property as follows:

java.rmi.server.codebase=file://dev/salsa/classes 

And give the program another try. This time, I got a different exception.

Exception in thread "main" java.security.AccessControlException:    
access denied (java.io.FilePermission //dev/salsa/classes read)
at java.security.AccessControlContext.checkPermission(AccessControlContext.java:264)
at java.security.AccessController.checkPermission(AccessController.java:427)
at java.lang.SecurityManager.checkPermission(SecurityManager.java:532)
at java.lang.SecurityManager.checkRead(SecurityManager.java:871)
... 

Hmm...this looks like we need some permissions granted. That's easy, let me go the $JRE/lib/security directory and change the java.policy file and add a new grant permission and it should all be fine. So I edit the java.policy file and add the grant permission:

grant codeBase "file://dev/salsa/classes" {
permission java.io.FilePermission "<<ALL FILES>>", "read";
};

I run the program thinking I fixed the problem for good. But not so fast! I see the same exception again. Then it hit me again. I had committed another silly error. It appears that I gave 2 slashes (file://...) to the codebase to separate the protocol and the url.

So I quickly undo the changes I made to the java.policy file. I go back to the codebase property and this time I set it as follows:

java.rmi.server.codebase=file:/dev/salsa/classes

I restart my RMI server and voila! Everything works fine this time!

Thought this record of my silly errors might help someone else sometime.

_{[J] Thanks to Jeremy Pitten for reminding me the codebase settings.}