Troubleshooting Client Server Connections

Client-Server Troubleshooting

This page is in the very early stages.

The first thing to do is to look at any messages on the console. The most fundamental error that can arise is the following exception

SEVERE: java.rmi.ConnectException: Connection refused to host: localhost; nested exception is: 
	java.net.ConnectException: Connection refused
	at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:574)
	at sun.rmi.transport.tcp.TCPChannel.createConnection(TCPChannel.java:185)
	at sun.rmi.transport.tcp.TCPChannel.newConnection(TCPChannel.java:171)
	at sun.rmi.server.UnicastRef.newCall(UnicastRef.java:306)
	at sun.rmi.registry.RegistryImpl_Stub.lookup(Unknown Source)
	at java.rmi.Naming.lookup(Naming.java:84)
	at edu.stanford.smi.protege.server.ServerPanel.connectToHost(ServerPanel.java:140)

Note that the exception happens when trying to call Naming.lookup. Usually the client will pop up a window that says Unable to Connect to Server. This means that the client could not connect to the rmiregistry. Possibly the rmiregistry is not running or there is a firewall or other network problem.

An alternate very different error is the following exception

SEVERE: java.rmi.ConnectException: Connection refused to host: 127.0.1.1; nested exception is: 
	java.net.ConnectException: Connection refused
	at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:574)
	at sun.rmi.transport.tcp.TCPChannel.createConnection(TCPChannel.java:185)
	at sun.rmi.transport.tcp.TCPChannel.newConnection(TCPChannel.java:171)
	at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:94)
	at edu.stanford.smi.protege.server.Server_Stub.openSession(Unknown Source)
	at edu.stanford.smi.protege.server.ServerPanel.createSession(ServerPanel.java:154)

This is usually accompanied by the message Failed to create a session because of either an invalid username/password combination, or a firewall problem. Unfortunately this pop up dialog is very ambiguous and can mean many things. It is for this reason that we have tried to add some additional information to help. In any case the exception tells us two very important things. First the problem occurs during an attempt ot create a session (ServerPanel.createSession) when the client makes a call to the server (Server_Stub.openSession(Unknown Source). The error that occured is Connection refused

It helps to look at the section documenting how the rmi connection is established just to understand the difference between successfully connecting to the rmiregistry and connecting to the server.