rmi class can not found exception

I wrote an simple project using java rmi and exported to an executable jar file. When I tries to run it, sometimes i got exceptions and sometimes it works. When I specify -Djava.rmi.server.codebase=file:serverClasses/, it seems it didn't create the jar file correctly. Here is the stacktrace:

java.rmi.ServerException: RemoteException occurred in server thread; nested exception is: 
    java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is: 
    java.lang.ClassNotFoundException: com.ServerBootstrap.IServer
    at sun.rmi.server.UnicastServerRef.oldDispatch(UnicastServerRef.java:413)
    at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:267)
    at sun.rmi.transport.Transport$1.run(Transport.java:177)
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.rmi.transport.Transport.serviceCall(Transport.java:173)
    at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:553)
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:808)
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:667)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
    at java.lang.Thread.run(Thread.java:636)
    at sun.rmi.transport.StreamRemoteCall.exceptionReceivedFromServer(StreamRemoteCall.java:273)
    at sun.rmi.transport.StreamRemoteCall.executeCall(StreamRemoteCall.java:251)
    at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:377)
    at sun.rmi.registry.RegistryImpl_Stub.rebind(Unknown Source)
    at java.rmi.Naming.rebind(Naming.java:177)
    at com.v3q6.eece411.A2.ServerBootstrap.ChatRoomServer.main(ChatRoomServer.java:37)
Caused by: java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is: 
    java.lang.ClassNotFoundException: com.ServerBootstrap.IServer
    at sun.rmi.registry.RegistryImpl_Skel.dispatch(Unknown Source)
    at sun.rmi.server.UnicastServerRef.oldDispatch(UnicastServerRef.java:403)
    at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:267)
    at sun.rmi.transport.Transport$1.run(Transport.java:177)
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.rmi.transport.Transport.serviceCall(Transport.java:173)
    at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:553)
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:808)
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:667)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
    at java.lang.Thread.run(Thread.java:636)
Caused by: java.lang.ClassNotFoundException: com.ServerBootstrap.IServer
    at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:323)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:268)
    at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:336)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:264)
    at sun.rmi.server.LoaderHandler.loadProxyInterfaces(LoaderHandler.java:728)
    at sun.rmi.server.LoaderHandler.loadProxyClass(LoaderHandler.java:672)
    at sun.rmi.server.LoaderHandler.loadProxyClass(LoaderHandler.java:609)
    at java.rmi.server.RMIClassLoader$2.loadProxyClass(RMIClassLoader.java:646)
    at java.rmi.server.RMIClassLoader.loadProxyClass(RMIClassLoader.java:311)
    at sun.rmi.server.MarshalInputStream.resolveProxyClass(MarshalInputStream.java:255)
    at java.io.ObjectInputStream.readProxyDesc(ObjectInputStream.java:1548)
    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1510)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1749)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1346)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:368)
    ... 12 more

It seems the program doesn't recognize the codebase. In my case, all the files are local. Does anyone know what is the problem? thanks

回答1:

Try explicitly specifying the name of the JAR file containing the com.ServerBootstrap.IServer class in your codebase, e.g.

-Djava.rmi.server.codebase=file:serverClasses/myjarfile.jar

The "Dynamic code downloading using JavaTM RMI (Using the java.rmi.server.codebase Property)" doc provides more information on the use of codebase and the options for its specification.

回答2:

With a relative path specified for java.rmi.server.codebase, make sure that you are in the correct directory (the parent directory of "serverClasses") when starting the client. If that's hard to ensure, an absolute path for the codebase might be more reliable.

Also, remember that when running with the -jar option, the -classpath option is completely ignored. I don't think that's a problem here; the RMIClassLoader should still be able to work using the server's codebase setting. But if you are relying on the client having access to additional classes specified on the classpath, that won't work. You'll need to use the Class-path attribute in the main JAR file's manifest.

回答3:

That's not a complete stacktrace, and I think you may have left out the part that shows the root cause of your problem.

If I recall correctly, ClassNotFoundException can sometimes be due to an exception thrown during static initialization of the class that is being loaded, or some class that it depends on. If this occurs, it will show up as a nested exception in the first stacktrace for the problem, at the next level of nesting. I recall (maybe incorrectly) that if your application repeats the attempted class load, the initialization exception is not in the resulting stacktrace.

EDIT: The complete stacktrace says that my theory is not correct.