GWT: jetty throws nullpointer exception on debugging

Question

i am currently working on gwt web app, which is nearly finished, but now i get the following warnings while debugging the project as web application:

Jan 10, 2012 5:13:55 PM com.google.apphosting.utils.jetty.JettyLogger warn
WARNING: failed greetServlet: java.lang.NullPointerException
Jan 10, 2012 5:13:55 PM com.google.apphosting.utils.jetty.JettyLogger warn
WARNING: Failed startup of context com.google.appengine.tools.development.DevAppEngineWebAppContext@29ef4453{/,/home/ich/Eclipse Workspace/Mein Wochenplaner/war}
java.lang.NullPointerException
at java.lang.Class.isAssignableFrom(Native Method)
at org.mortbay.jetty.servlet.ServletHolder.doStart(ServletHolder.java:256)
at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
at org.mortbay.jetty.servlet.ServletHandler.initialize(ServletHandler.java:685)
at org.mortbay.jetty.servlet.Context.startContext(Context.java:140)
at org.mortbay.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1250)
at org.mortbay.jetty.handler.ContextHandler.doStart(ContextHandler.java:517)
at org.mortbay.jetty.webapp.WebAppContext.doStart(WebAppContext.java:467)
at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
at org.mortbay.jetty.handler.HandlerWrapper.doStart(HandlerWrapper.java:130)
at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
at org.mortbay.jetty.handler.HandlerWrapper.doStart(HandlerWrapper.java:130)
at org.mortbay.jetty.Server.doStart(Server.java:224)
at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
at com.google.appengine.tools.development.JettyContainerService.startContainer(JettyContainerService.java:191)
at com.google.appengine.tools.development.AbstractContainerService.startup(AbstractContainerService.java:239)
at com.google.appengine.tools.development.DevAppServerImpl.start(DevAppServerImpl.java:146)
at com.google.appengine.tools.development.gwt.AppEngineLauncher.start(AppEngineLauncher.java:97)
at com.google.gwt.dev.DevMode.doStartUpServer(DevMode.java:509)
at com.google.gwt.dev.DevModeBase.startUp(DevModeBase.java:1068)
at com.google.gwt.dev.DevModeBase.run(DevModeBase.java:811)
at com.google.gwt.dev.DevMode.main(DevMode.java:311)
Jan 10, 2012 5:13:55 PM com.google.appengine.tools.development.DevAppServerImpl start
INFO: The server is running at http://localhost:8888/
Jan 10, 2012 5:13:55 PM com.google.appengine.tools.development.DevAppServerImpl start
INFO: The admin console is running at http://localhost:8888/_ah/admin

Eclipse still gives me an url, but when i open it, i get an http

503 error, service unavailable

because my start html could not be accessed.

Answer 1

I had a similar problem. Turns out that when I created a Web Application Project template with some sample code, a servlet entry was being added to web.xml without any corresponding servlet code.

Simply removed the redundant entries, rolled my own servlets, and it worked fine

Answer 2

Make sure the value in your web.xml document points to the correct class. See the example below:

 ...
  <servlet>
    <servlet-name>greetServlet</servlet-name>
    <servlet-class>package.GreetServiceImpl</servlet-class>
  </servlet>
...

package.GreetServiceImpl should exist in your project.

Note: this might have been caused by renaming your classes.