ClassCastException on App Engine Server

Question

I am getting a ClassCastException when running a Google AppEngine (1.9.8) project in Eclipse development mode that otherwise works fine as a stand alone java application.

The below method throws the exception on the last line when trying to create a new instance using a Class object.

public FixGroupMgr getGroupMgr(String fixVersion)
    throws ClassNotFoundException, InstantiationException,
    IllegalAccessException {
    String versionIdent = fixVersion.replaceAll("[\",.]", "") + "Mgr";
    FixGroupMgr.cleanStaticData();
    Class<?> c =
        ClassLoader.getSystemClassLoader().loadClass(
            "com.globalforge.infix." + versionIdent);
    return (FixGroupMgr) c.newInstance();
}

versionIdent = "FIX44Mgr" after replaceAll() is called.

com.globalforge.infix.FIX44Mgr
extends
com.globalforge.infix.FixGroupMgr

I have verified that both class files are present in the jar file I have placed in WEB-INF/lib.

[1378880913@qtp-935467774-0] ERROR com.globalforge.infix.FixRulesTransformVisitor - Bad     message or unsupported fix version....parser HALT.

java.lang.ClassCastException: com.globalforge.infix.FIX44Mgr cannot be cast to   com.globalforge.infix.FixGroupMgr

at com.globalforge.infix.FixContextMgr.getGroupMgr(FixContextMgr.java:43)
at com.globalforge.infix.FixMessageMgr.init(FixMessageMgr.java:157)
at com.globalforge.infix.FixMessageMgr.parseField(FixMessageMgr.java:138)
at com.globalforge.infix.FixMessageMgr.parseMessage(FixMessageMgr.java:112)
at com.globalforge.infix.FixMessageMgr.<init>(FixMessageMgr.java:50)
at com.globalforge.infix.FixRulesTransformVisitor.visitParseRules(FixRulesTransformVisitor.java:68)
at com.globalforge.infix.FixRulesTransformVisitor.visitParseRules(FixRulesTransformVisitor.java:31)
at com.globalforge.infix.antlr.FixRulesParser$ParseRulesContext.accept(FixRulesParser.java:85)
at org.antlr.v4.runtime.tree.AbstractParseTreeVisitor.visit(AbstractParseTreeVisitor.java:44)
at com.globalforge.infix.FixRulesEngine.transformMsg(FixRulesEngine.java:99)
at com.globalforge.infix.server.ExampleAppServiceImpl.transformMsg(ExampleAppServiceImpl.java:26)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at com.google.appengine.tools.development.agent.runtime.Runtime.invoke(Runtime.java:115)
at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:561)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:265)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.processPost(RemoteServiceServlet.java:305)
at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doPost(AbstractRemoteServiceServlet.java:62)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
at com.googlecode.objectify.cache.AsyncCacheFilter.doFilter(AsyncCacheFilter.java:58)
at com.googlecode.objectify.ObjectifyFilter.doFilter(ObjectifyFilter.java:48)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.api.socket.dev.DevSocketFilter.doFilter(DevSocketFilter.java:74)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.ResponseRewriterFilter.doFilter(ResponseRewriterFilter.java:127)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.HeaderVerificationFilter.doFilter(HeaderVerificationFilter.java:34)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:63)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:125)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.DevAppServerModulesFilter.doDirectRequest(DevAppServerModulesFilter.java:366)
at com.google.appengine.tools.development.DevAppServerModulesFilter.doDirectModuleRequest(DevAppServerModulesFilter.java:349)
at com.google.appengine.tools.development.DevAppServerModulesFilter.doFilter(DevAppServerModulesFilter.java:116)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
at com.google.appengine.tools.development.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:98)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:491)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:326)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:938)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:755)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)

Answer 1

Make sure this class is not present in two different jars. For example, if an older version of a jar is still present, you may get this error.

Answer 2

I was able to work around the problem by avoiding the system class loader.

As a sanity test, I deployed my application in a Tomcat 7 web container and was surprised to find a similar Exception (ClassNotFoundException) being thrown in the same method.

As a work-around, I instead used the class loader that loaded the class making the call and it worked. I then deployed the fix to Google AppEngine and it also worked.

After poking around a little, I found that many web containers insulate the system class loader from applications which can result in these types of behaviors.

Here is the fix:

public FixGroupMgr getGroupMgr(String fixVersion)
    throws ClassNotFoundException, InstantiationException,
    IllegalAccessException {
    String versionIdent = fixVersion.replaceAll("[\",.]", "") + "Mgr";
    FixGroupMgr.cleanStaticData();
    /*
     * Class<?> c = ClassLoader.getSystemClassLoader().loadClass(
     * "com.globalforge.infix." + versionIdent);
     */
    Class<?> c =
        FixContextMgr.class.getClassLoader().loadClass(
            "com.globalforge.infix." + versionIdent);
    return (FixGroupMgr) c.newInstance();
}