RMI, dynamically load class into server, rmiregistry CLASSPATH

[John Denton]

Hello.

I've done some RMI examples before but I haven't tried dynamically loading code to server yet. So I looked up RMI tutorial and slightly modified the example. First I started rmiregistry in my home directory (eg. away from CLASSPATH of my two projects), then I created server & client projects. The reason for two projects is to not share CLASSPATH. Then I tried to execute server main() (compute/ComputeEngine.java) but RMI fails to get shared/Compute.java interface (exception & code below). I tried to start registry inside server main() (eg. createRegistry(int) instead of getRegistry(int)) or start rmiregistry program in directory with compiled server classes and server startup worked. However now client main() (client/ComputeLong.java) threw same exception. According to tutorial, rmiregistry shouldn't have access to any CLASSPATH. My goal is to execute class unknown to server (implementing common interface) in server. What am I doing wrong? Thank you.

Server:

src/
├── compute
│   └── ComputeEngine.java
└── shared
    ├── Compute.java
    ├── MyPermissionCollection.java
    ├── MyPolicy.java
    └── Task.java

compute/ComputeEngine.java:

package compute;

import shared.Compute;
import shared.MyPolicy;
import shared.Task;

import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;
import java.rmi.server.UnicastRemoteObject;
import java.security.Policy;

public class ComputeEngine implements Compute {

	public <T> T executeTask(Task<T> t) {
		return t.execute();
	}

	public static void main(String[] args) {
		Policy.setPolicy(new MyPolicy());
		if (System.getSecurityManager() == null) {
			System.setSecurityManager(new SecurityManager());
		}
		try {
			String name = "Compute";
			Compute engine = new ComputeEngine();
			Compute stub =
					(Compute) UnicastRemoteObject.exportObject(engine, 0);
			Registry registry = LocateRegistry.getRegistry(1099);
			registry.rebind(name, stub);
			System.out.println("ComputeEngine bound");
		} catch (Exception e) {
			System.err.println("ComputeEngine exception:");
			e.printStackTrace();
		}
	}
}

Client:

src/
├── client
│   ├── ComputeLong.java
│   └── LongTask.java
└── shared
    ├── Compute.java
    ├── MyPermissionCollection.java
    ├── MyPolicy.java
    └── Task.java

client/ComputeLong:

package client;

import shared.Compute;
import shared.MyPolicy;

import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;
import java.security.Policy;

public class ComputeLong {
	public static void main(String args[]) {
		Policy.setPolicy(new MyPolicy());
		if (System.getSecurityManager() == null) {
			System.setSecurityManager(new SecurityManager());
		}
		try {
			String name = "Compute";
			Registry registry = LocateRegistry.getRegistry(1099);
			Compute comp = (Compute) registry.lookup(name);
			LongTask task = new LongTask();
			Long pi = comp.executeTask(task);
			System.out.println(pi);
		} catch (Exception e) {
			System.err.println("ComputeLong exception:");
			e.printStackTrace();
		}
	}
}

client/LongTask.java

package client;

import shared.Task;

import java.io.Serializable;

public class LongTask implements Task<Long>, Serializable {

	private static final long serialVersionUID = 1337l;

	public Long execute() {
		return 1337l;
	}
}

Shared:
shared/Compute.java:

package shared;

import java.rmi.Remote;
import java.rmi.RemoteException;

public interface Compute extends Remote {
	<T> T executeTask(Task<T> t) throws RemoteException;
}

shared/Task.java:

package shared;

public interface Task<T> {
	T execute();
}

For clarity I omitted policy related files (they work, I tried it with command line settings too). Task and Compute interfaces are copy-pasted between projects but they're same.

This exception is from server project, but it looks exactly same in client (rmi-test-client):

/opt/java/jdk1.6.0_30/bin/java -Didea.launcher.port=7534 -Didea.launcher.bin.path=/home/un/apps/idea-IC-111.167/bin -Dfile.encoding=UTF-8 -classpath /opt/java/jdk1.6.0_30/jre/lib/resources.jar:/opt/java/jdk1.6.0_30/jre/lib/alt-string.jar:/opt/java/jdk1.6.0_30/jre/lib/alt-rt.jar:/opt/java/jdk1.6.0_30/jre/lib/management-agent.jar:/opt/java/jdk1.6.0_30/jre/lib/jce.jar:/opt/java/jdk1.6.0_30/jre/lib/rt.jar:/opt/java/jdk1.6.0_30/jre/lib/jsse.jar:/opt/java/jdk1.6.0_30/jre/lib/charsets.jar:/opt/java/jdk1.6.0_30/jre/lib/plugin.jar:/opt/java/jdk1.6.0_30/jre/lib/javaws.jar:/opt/java/jdk1.6.0_30/jre/lib/deploy.jar:/opt/java/jdk1.6.0_30/jre/lib/ext/dnsns.jar:/opt/java/jdk1.6.0_30/jre/lib/ext/sunpkcs11.jar:/opt/java/jdk1.6.0_30/jre/lib/ext/sunjce_provider.jar:/opt/java/jdk1.6.0_30/jre/lib/ext/localedata.jar:/home/un/work/rmi-test/out/production/rmi-test:/opt/scala/lib/scala-library.jar:/opt/scala/lib/scala-swing.jar:/opt/scala/lib/scala-dbc.jar:/home/un/apps/idea-IC-111.167/lib/idea_rt.jar com.intellij.rt.execution.application.AppMain compute.ComputeEngine
ComputeEngine exception:
java.rmi.ServerException: RemoteException occurred in server thread; nested exception is:
		java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is:
		java.lang.ClassNotFoundException: shared.Compute
		at sun.rmi.server.UnicastServerRef.oldDispatch(UnicastServerRef.java:419)
		at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:267)
		at sun.rmi.transport.Transport$1.run(Transport.java:177)
		at sun.rmi.transport.Transport$1.run(Transport.java:174)
		at java.security.AccessController.doPrivileged(Native Method)
		at sun.rmi.transport.Transport.serviceCall(Transport.java:173)
		at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:553)
		at sun.rmi.transport.tcp.TCPTransport$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:722)
		at sun.rmi.transport.StreamRemoteCall.exceptionReceivedFromServer(StreamRemoteCall.java:255)
		at sun.rmi.transport.StreamRemoteCall.executeCall(StreamRemoteCall.java:233)
		at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:359)
		at sun.rmi.registry.RegistryImpl_Stub.rebind(Unknown Source)
		at compute.ComputeEngine.main(ComputeEngine.java:33)
		at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
		at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
		at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
		at java.lang.reflect.Method.invoke(Method.java:597)
		at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)
Caused by: java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is:
		java.lang.ClassNotFoundException: shared.Compute
		at sun.rmi.registry.RegistryImpl_Skel.dispatch(Unknown Source)
		at sun.rmi.server.UnicastServerRef.oldDispatch(UnicastServerRef.java:409)
		at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:267)
		at sun.rmi.transport.Transport$1.run(Transport.java:177)
		at sun.rmi.transport.Transport$1.run(Transport.java:174)
		at java.security.AccessController.doPrivileged(Native Method)
		at sun.rmi.transport.Transport.serviceCall(Transport.java:173)
		at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:553)
		at sun.rmi.transport.tcp.TCPTransport$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:722)
Caused by: java.lang.ClassNotFoundException: shared.Compute
		at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
		at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
		at java.security.AccessController.doPrivileged(Native Method)
		at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
		at java.lang.ClassLoader.loadClass(ClassLoader.java:423)
		at java.lang.ClassLoader.loadClass(ClassLoader.java:356)
		at java.lang.Class.forName0(Native Method)
		at java.lang.Class.forName(Class.java:264)
		at sun.rmi.server.LoaderHandler.loadProxyInterfaces(LoaderHandler.java:730)
		at sun.rmi.server.LoaderHandler.loadProxyClass(LoaderHandler.java:674)
		at sun.rmi.server.LoaderHandler.loadProxyClass(LoaderHandler.java:611)
		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:257)
		at java.io.ObjectInputStream.readProxyDesc(ObjectInputStream.java:1549)
		at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1511)
		at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1750)
		at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1347)
		at java.io.ObjectInputStream.readObject(ObjectInputStream.java:369)
		... 13 more