com.google.apphosting.utils.config.AppEngineConfigException: appengine-web.xml does not contain a element

Appengine thread troubleshoot:
com.google.apphosting.utils.config.AppEngineConfigException: appengine-web.xml does not contain a element.
See http://code.google.com/appengine/docs/java/config/appconfig.html#Using_Concurrent_Requests for more information.
You probably want to enable concurrent requests.
at com.google.apphosting.utils.config.AppEngineWebXmlReader.readAppEngineWebXml(AppEngineWebXmlReader.java:87)
at com.google.apphosting.utils.config.EarHelper.readWebModule(EarHelper.java:166)
at com.google.appengine.tools.development.ApplicationConfigurationManager$WarServerConfigurationHandle.readConfiguration(ApplicationConfigurationManager.java:399)
at com.google.appengine.tools.development.ApplicationConfigurationManager.(ApplicationConfigurationManager.java:146)
at com.google.appengine.tools.development.ApplicationConfigurationManager.newWarConfigurationManager(ApplicationConfigurationManager.java:88)
at com.google.appengine.tools.development.DevAppServerImpl.(DevAppServerImpl.java:138)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.google.appengine.tools.development.DevAppServerFactory.createDevAppServer(DevAppServerFactory.java:165)
at com.google.appengine.tools.development.DevAppServerFactory.createDevAppServer(DevAppServerFactory.java:69)
at com.google.appengine.tools.development.DevAppServerFactory.createDevAppServer(DevAppServerFactory.java:53)
at com.google.appengine.tools.development.gwt.AppEngineLauncher.start(AppEngineLauncher.java:84)
at com.google.gwt.dev.DevMode.doStartUpServer(DevMode.java:500)
at com.google.gwt.dev.DevModeBase.startUp(DevModeBase.java:1055)
at com.google.gwt.dev.DevModeBase.run(DevModeBase.java:804)
at com.google.gwt.dev.DevMode.main(DevMode.java:309)
   [ERROR] Unable to start App Engine server
Resolution:
Add threadsafe tag value as true to the appengine-web.xml in war\WEB-INF folder.

Eclipse GWT Junit Error: java.lang.NoSuchMethodError: org.mortbay.thread.Timeout

If you see below errors while running GWT unit test, then change the sequence of libraries. Right click on the project in Eclipse. Navigate to Build path --> Configure Build path --> Order and Export. Change the sequence to GWT then Appengine.
Error is below: java.lang.NoSuchMethodError: org.mortbay.thread.Timeout.(Ljava/lang/Object;)V at org.mortbay.io.nio.SelectorManager$SelectSet.(SelectorManager.java:306) at org.mortbay.io.nio.SelectorManager.doStart(SelectorManager.java:223) at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:39) at org.mortbay.jetty.nio.SelectChannelConnector.doStart(SelectChannelConnector.java:303) at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:39) at org.mortbay.jetty.Server.doStart(Server.java:233) at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:39) at com.google.gwt.dev.shell.jetty.JettyLauncher.start(JettyLauncher.java:542) at com.google.gwt.dev.DevMode.doStartUpServer(DevMode.java:431) at com.google.gwt.dev.DevModeBase.startUp(DevModeBase.java:1053) at com.google.gwt.junit.JUnitShell.getUnitTestShell(JUnitShell.java:680) at com.google.gwt.junit.JUnitShell.runTest(JUnitShell.java:625) at com.google.gwt.junit.client.GWTTestCase.runTest(GWTTestCase.java:456) at junit.framework.TestCase.runBare(TestCase.java:134) at junit.framework.TestResult$1.protect(TestResult.java:110) at junit.framework.TestResult.runProtected(TestResult.java:128) at junit.framework.TestResult.run(TestResult.java:113) at junit.framework.TestCase.run(TestCase.java:124) at com.google.gwt.junit.client.GWTTestCase.run(GWTTestCase.java:311) at junit.framework.TestSuite.runTest(TestSuite.java:232) at junit.framework.TestSuite.run(TestSuite.java:227) at org.junit.internal.runners.JUnit38ClassRunner.run(JUnit38ClassRunner.java:83) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:49) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390) at 

[ERROR] Unable to start AppEngine server java.lang.RuntimeException: Unable to restore the previous TimeZone

 [ERROR] Unable to start AppEngine server
java.lang.RuntimeException: Unable to restore the previous TimeZone
at com.google.appengine.tools.development.DevAppServerImpl.restoreLocalTimeZone(DevAppServerImpl.java:290)
at com.google.appengine.tools.development.DevAppServerImpl.start(DevAppServerImpl.java:228)
at com.google.appengine.tools.development.gwt.AppEngineLauncher.start(AppEngineLauncher.java:119)
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)
Caused by: java.lang.NoSuchFieldException: defaultZoneTL
at java.lang.Class.getDeclaredField(Class.java:1882)
at com.google.appengine.tools.development.DevAppServerImpl.restoreLocalTimeZone(DevAppServerImpl.java:284)

To resolve the above issue set the following JVM argument.

-Dappengine.user.timezone.impl=UTC

javax.xml.parsers.FactoryConfigurationError: Provider org.apache.xerces.jaxp.SAXParserFactoryImpl not found

This happens when gwt-gadget.jar is added to the build path. Remove any SAXParserFactoryImpl class from your build path (Remove the $JAVA_HOME/jre/lib/jaxp.properties fixed the issue.)

[WARN] failed JettyContainerService$ApiProxyHandler@4478de9f: javax.xml.parsers.FactoryConfigurationError: Provider org.apache.xerces.jaxp.SAXParserFactoryImpl not found
[WARN] Error starting handlers
javax.xml.parsers.FactoryConfigurationError: Provider org.apache.xerces.jaxp.SAXParserFactoryImpl not found
at javax.xml.parsers.SAXParserFactory.newInstance(SAXParserFactory.java:134)
at org.mortbay.xml.XmlParser.setValidating(XmlParser.java:91)
at org.mortbay.xml.XmlParser.(XmlParser.java:83)
at org.mortbay.jetty.webapp.TagLibConfiguration.configureWebApp(TagLibConfiguration.java:210)
at org.mortbay.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1247)
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:186)
at com.google.appengine.tools.development.AbstractContainerService.startup(AbstractContainerService.java:162)
at com.google.appengine.tools.development.DevAppServerImpl.start(DevAppServerImpl.java:172)
at com.google.appengine.tools.development.gwt.AppEngineLauncher.start(AppEngineLauncher.java:119)
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)
[WARN] Nested in javax.xml.parsers.FactoryConfigurationError: Provider org.apache.xerces.jaxp.SAXParserFactoryImpl not found:
java.lang.ClassNotFoundException: org.apache.xerces.jaxp.SAXParserFactoryImpl
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at com.google.appengine.tools.development.IsolatedAppClassLoader.loadClass(IsolatedAppClassLoader.java:176)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
at javax.xml.parsers.FactoryFinder.getProviderClass(FactoryFinder.java:111)
at javax.xml.parsers.FactoryFinder.newInstance(FactoryFinder.java:146)
at javax.xml.parsers.FactoryFinder.findJarServiceProvider(FactoryFinder.java:298)
at javax.xml.parsers.FactoryFinder.find(FactoryFinder.java:223)
at javax.xml.parsers.SAXParserFactory.newInstance(SAXParserFactory.java:128)
at org.mortbay.xml.XmlParser.setValidating(XmlParser.java:91)
at org.mortbay.xml.XmlParser.(XmlParser.java:83)
at org.mortbay.jetty.webapp.TagLibConfiguration.configureWebApp(TagLibConfiguration.java:210)
at org.mortbay.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1247)
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:186)
at com.google.appengine.tools.development.AbstractContainerService.startup(AbstractContainerService.java:162)
at com.google.appengine.tools.development.DevAppServerImpl.start(DevAppServerImpl.java:172)
at com.google.appengine.tools.development.gwt.AppEngineLauncher.start(AppEngineLauncher.java:119)
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)