在Tomcat 7中运行RMI客户端得到ClassNotFoundException

Question

I am having some difficulties with RMI and Tomcat. This is the big picture of this project I am working on: the RMI client is called by a Java servlet that runs in Tomcat, the servlet accept user input and pass the parameters to the RMI client. Then the RMI client then calls the RMI server to run the heavy compuation part. The problem is that although everything works fine without hosting the RMI client in the Tomcat server, it doesn't run once I put it in Tomcat. Here are some configurations: I DID NOT set up the security manager in the code, I assume that Tomcat will use its own.

    //if (System.getSecurityManager() == null) {
    //    System.setSecurityManager(new SecurityManager());
    //}

I also set the permission as following:

$CATALINA_HOME/conf/catalina.policy

grant codeBase "file:${catalina.home}/webapps/MyAPP/WEB-INF/classes/-" { 
    permission java.security.AllPermission "", ""; }; 
grant codeBase "file:${catalina.home}/webapps/MyAPP/WEB-INF/lib/-" { 
    permission java.security.AllPermission "", ""; 
}; 
grant codeBase "file:${catalina.home}/webapps/MyAPP/WEB-INF/lib/some-common-3.0.jar" { 
    permission java.io.FilePermission "*", "read, write"; 
};

Other than these two configurations, I didn't set any java.rmi.server.codebase or java.security.policy.

I got the following error by submitting the code from RMI client to RMI server:

java.rmi.ServerException: RemoteException occurred in server thread; nested exception is: 
java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is: 
java.lang.ClassNotFoundException: mypackage.SomeClass
at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:334)
at sun.rmi.transport.Transport$1.run(Transport.java:159)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.Transport.serviceCall(Transport.java:155)
at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:535)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:790)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:649)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
at sun.rmi.transport.StreamRemoteCall.exceptionReceivedFromServer(StreamRemoteCall.java:255)
at sun.rmi.transport.StreamRemoteCall.executeCall(StreamRemoteCall.java:233)
at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:142)
at java.rmi.server.RemoteObjectInvocationHandler.invokeRemoteMethod(RemoteObjectInvocationHandler.java:178)
at java.rmi.server.RemoteObjectInvocationHandler.invoke(RemoteObjectInvocationHandler.java:132)
at com.sun.proxy.$Proxy19.executeTask(Unknown Source)
at cluster.server.centralservice.CentralManagementServer.submitJob(CentralManagementServer.java:232)
at cluster.server.centralservice.JobSubmitter.runJob(JobSubmitter.java:226)
at cluster.server.centralservice.JobSubmitter.doPost(JobSubmitter.java:144)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
at java.lang.Thread.run(Thread.java:662)
Caused by: java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is: 
java.lang.ClassNotFoundException: mypackage.SomeClass

I have been stuck here for a few days. Most examples I searched online is outdated and do not cover the RMI with Tomcat set up. Can anybody help? Many thanks.

Answer 1

as the exception says

java.lang.ClassNotFoundException: mypackage.SomeClass

this happens coz RMI is using a seperate class loader which isn't able to see SomeClass .

Add <Loader delegate="true"/> into context.xml file (to Context element) in tomcat/conf directory.

This change fixed a similar issue I faced (not particularly with RMI) but worth a try.