Strange problem with gwt, tomcat and memcached

[Jeremiah Elliott]

ok, I am not even 100% sure this is a GWT issue. The more I mess with it the more I am convinced that it is somehow gwt related. Anyway I am in the process of adding memcache to the application I am working on. In hosted mode it worked exactly as expected. Huge speed improvement, and the memcached log shows my objects going in and out as expected. The problem is that when i publish the application to tomcat the cache doesn't work. I can still add items to the cache, but when i pull items out of the cache I get a class not found exception.
Initially I thought that the problem may be because the object being cached lives in the client package. (com.sagus.client.Report) I createdd a shared package as discribed here
http://groups.google.com/group/Google-Web-Toolkit/browse_thread/thread/51a8a9bb3f141ab4/c43fcc7dad3f7fde?lnk=gst&q=foo.bar.shared#c43fcc7dad3f7fde
however this didnt' solve the problem. I could still set and get the Report object in Hosted Mode but in production on tomcat I got the same message. Here is the stacktrace:
java.lang.ClassNotFoundException: com.sagus.Shared.Report
    at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
    at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:247)
    ......



Well, clearly it can find com.sagus.Shared.Report because is putting it into memcache just fine. In a last act of desperation, i exported the contents of src into a jar file using eclipse export feature, and dumped that into Tomcat's lib directory. Now I am getting a ClassCastException:

2008-11-22 12:33:57,425 : ERROR : com.sagus.server.DataCache.getWidget(DataCache.java:27) : get widget 18: 
java.lang.ClassCastException: com.sagus.Shared.Report cannot be cast to com.sagus.Shared.Report
    at com.sagus.server.DataCache.getWidget(DataCache.java:25)
    at com.sagus.server.SagusDashImpl.getReportById(SagusDashImpl.java:244)
    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.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:527)
    at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:164)
    at com.google.gwt.user.server.rpc.RemoteServiceServlet.doPost(RemoteServiceServlet.java:86)
    ......




This is the class I am using to do the memcache sets and gets:

package com.sagus.server;

import java.io.IOException;
import java.net.InetSocketAddress;
import net.spy.memcached.MemcachedClient;
import org.apache.log4j.Logger;
import com.sagus.Shared.Report;

public class DataCache {
    private static final Logger        logger            = SagusDashImpl.getLogger();
    private static String            WIDGET_PREFIX    = "PROD_WIDGET_";
    private static MemcachedClient    c                = null;

    public DataCache() {
        try {
            c = new MemcachedClient(new InetSocketAddress("localhost", 11211));
        } catch (IOException ioe) {
            logger.error("init DataCache ", ioe);
        }
    }

    public Report getWidget(int id) {
        Report r = null;
        try {
            r = (Report) c.get(WIDGET_PREFIX + id);
        } catch (Exception e) {
            logger.error("get widget " + id + ": ", e);
        }
        return r;
    }

    public void cacheWidget(Report report) {
        try {
            c.set(WIDGET_PREFIX + report.getWidgetId(), 360000, report);
        } catch (Exception e) {
            logger.error("cacheWidget ", e);
        }
    }


Here is the object being cached, its just a pojo:

package com.sagus.Shared;
import java.util.ArrayList;
import java.util.Date;
import com.google.gwt.user.client.rpc.IsSerializable;

public class Report implements IsSerializable, java.io.Serializable {
....
}


On one hand I wonder if its because it is implementing two different serializable interfaces, but when i build this same object from the database it works just fine.
At this point I am totally out of ideas. Any pointers would be helpful.
   
-Jeremiah

[Jeremiah Elliott]

Ok, still having issues with this... Has anyone here used memcached with gwt? I am starting to thing the problem is because the Report object is both IsSerializable and  java.io.Serializable?  Any kind of pointer would be good. Thanks
-Jeremiah

[Jeremiah Elliott]

Well, the problem was due to the tomcat classloader. Not sure why, but when i packaged the memcached jar in the war file (It had been in tomcat's top level lib directory) it worked! Not a GWT issue. ;-)

-Jeremiah