GWT 1.6 with Hibernate and class loading issues.

[sajil]

When I am trying to connect to MySQL from my GWT servlet, I am getting
an exception :

java.security.AccessControlException: access denied
(java.lang.RuntimePermission modifyThreadGroup)

I searched the group and found the solution. I went and disabled the
Google App Engine. But now I have problem with my class loading. It
seams the GWT class loader is conflicting with Eclipse class loader. I
get the following error:

May 18, 2009 11:10:30 PM net.sf.hibernate.dialect.Dialect <init>
INFO: Using dialect: net.sf.hibernate.dialect.MySQLDialect
Initial SessionFactory creation
failed.org.hibernate.HibernateException: Could not instantiate dialect
class
org.hibernate.HibernateException: Could not instantiate dialect class
at org.hibernate.dialect.DialectFactory.buildDialect
(DialectFactory.java:107)
at org.hibernate.dialect.DialectFactory.buildDialect
(DialectFactory.java:65)
at org.hibernate.cfg.SettingsFactory.determineDialect
(SettingsFactory.java:460)
at org.hibernate.cfg.SettingsFactory.buildSettings
(SettingsFactory.java:155)
at org.hibernate.cfg.Configuration.buildSettings(Configuration.java:
2101)
at org.hibernate.cfg.Configuration.buildSessionFactory
(Configuration.java:1325)
at com.bt.web.server.HibernateUtil.<clinit>(HibernateUtil.java:13)
at com.bt.web.server.EventManager.createAndStoreEvent
(EventManager.java:22)
at com.bt.web.server.GreetingServiceImpl.greetServer
(GreetingServiceImpl.java:23)
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:166)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.doPost
(RemoteServiceServlet.java:86)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:713)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:806)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:
487)
at org.mortbay.jetty.servlet.ServletHandler.handle
(ServletHandler.java:362)
at org.mortbay.jetty.security.SecurityHandler.handle
(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle
(SessionHandler.java:181)
at org.mortbay.jetty.handler.ContextHandler.handle
(ContextHandler.java:729)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:
405)
at org.mortbay.jetty.handler.HandlerWrapper.handle
(HandlerWrapper.java:152)
at org.mortbay.jetty.handler.RequestLogHandler.handle
(RequestLogHandler.java:49)
at org.mortbay.jetty.handler.HandlerWrapper.handle
(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:324)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:
505)
at org.mortbay.jetty.HttpConnection$RequestHandler.content
(HttpConnection.java:843)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:647)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:205)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:380)
at org.mortbay.io.nio.SelectChannelEndPoint.run
(SelectChannelEndPoint.java:396)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run
(QueuedThreadPool.java:488)
Caused by: java.lang.ClassCastException:
net.sf.hibernate.dialect.MySQLDialect cannot be cast to
org.hibernate.dialect.Dialect
at org.hibernate.dialect.DialectFactory.buildDialect
(DialectFactory.java:101)
... 34 more
java.lang.NullPointerException
at com.bt.web.server.EventManager.createAndStoreEvent
(EventManager.java:22)
at com.bt.web.server.GreetingServiceImpl.greetServer
(GreetingServiceImpl.java:23)
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:166)
at com.google.gwt.user.server.rpc.RemoteServiceServlet.doPost
(RemoteServiceServlet.java:86)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:713)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:806)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:
487)
at org.mortbay.jetty.servlet.ServletHandler.handle
(ServletHandler.java:362)
at org.mortbay.jetty.security.SecurityHandler.handle
(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle
(SessionHandler.java:181)
at org.mortbay.jetty.handler.ContextHandler.handle
(ContextHandler.java:729)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:
405)
at org.mortbay.jetty.handler.HandlerWrapper.handle
(HandlerWrapper.java:152)
at org.mortbay.jetty.handler.RequestLogHandler.handle
(RequestLogHandler.java:49)
at org.mortbay.jetty.handler.HandlerWrapper.handle
(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:324)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:
505)
at org.mortbay.jetty.HttpConnection$RequestHandler.content
(HttpConnection.java:843)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:647)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:205)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:380)
at org.mortbay.io.nio.SelectChannelEndPoint.run
(SelectChannelEndPoint.java:396)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run
(QueuedThreadPool.java:488)


Please help

Sajil

[Sumit Chandel]

Hi Sajil,

I believe the error you're receiving is due to a ClassCastException in your server-side code. From the exception stack trace:

Caused by: java.lang.ClassCastException:
net.sf.hibernate.dialect.MySQLDialect cannot be cast to
org.hibernate.dialect.Dialect
       at org.hibernate.dialect.DialectFactory.buildDialect
(DialectFactory.java:101)
       ... 34 more
java.lang.NullPointerException
       at com.bt.web.server.EventManager.createAndStoreEvent
(EventManager.java:22)
       at com.bt.web.server.GreetingServiceImpl.greetServer
(GreetingServiceImpl.java:23)

As far as launch configurations are concerned, you should be good to go now that the Google App Engine option has been de-selected.

Hope that helps,

-Sumit Chandel