Google app engine hello world program doesn't work

Question

I installed eclipse GAE plugin, followed this simple tutorial, and when I run my program I get the error message

    Initializing App Engine server
אוג 23, 2013 12:54:04 PM com.google.apphosting.utils.config.AppEngineWebXmlReader readAppEngineWebXml
INFO: Successfully processed C:\Users\Owner\workspace\GoogleTest2\war\WEB-INF/appengine-web.xml
אוג 23, 2013 12:54:04 PM com.google.apphosting.utils.config.AppEngineWebXmlReader readAppEngineWebXml
SEVERE: Received exception processing C:\Users\Owner\workspace\GoogleTest2\war\WEB-INF/appengine-web.xml
com.google.apphosting.utils.config.AppEngineConfigException: appengine-web.xml does not contain a <threadsafe> 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:85)
        at com.google.apphosting.utils.config.EarHelper.readWebModule(EarHelper.java:166)
        at com.google.appengine.tools.development.ApplicationConfigurationManager$WarModuleConfigurationHandle.readConfiguration(ApplicationConfigurationManager.java:399)
        at com.google.appengine.tools.development.ApplicationConfigurationManager.<init>(ApplicationConfigurationManager.java:146)
        at com.google.appengine.tools.development.ApplicationConfigurationManager.newWarConfigurationManager(ApplicationConfigurationManager.java:88)
        at com.google.appengine.tools.development.DevAppServerImpl.<init>(DevAppServerImpl.java:137)
        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:233)
        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:509)
        at com.google.gwt.dev.DevModeBase.startUp(DevModeBase.java:1093)
        at com.google.gwt.dev.DevModeBase.run(DevModeBase.java:836)
        at com.google.gwt.dev.DevMode.main(DevMode.java:311)

   [ERROR] Unable to start App Engine server
com.google.apphosting.utils.config.AppEngineConfigException: Invalid configuration
        at com.google.appengine.tools.development.DevAppServerImpl.reportDeferredConfigurationException(DevAppServerImpl.java:414)
        at com.google.appengine.tools.development.DevAppServerImpl.start(DevAppServerImpl.java:211)
        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:1093)
        at com.google.gwt.dev.DevModeBase.run(DevModeBase.java:836)
        at com.google.gwt.dev.DevMode.main(DevMode.java:311)
Caused by: com.google.apphosting.utils.config.AppEngineConfigException: Invalid appengine-web.xml(C:\Users\Owner\workspace\GoogleTest2\war\WEB-INF/appengine-web.xml) - appengine-web.xml does not contain a <threadsafe> 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.EarHelper.readWebModule(EarHelper.java:168)
        at com.google.appengine.tools.development.ApplicationConfigurationManager$WarModuleConfigurationHandle.readConfiguration(ApplicationConfigurationManager.java:399)
        at com.google.appengine.tools.development.ApplicationConfigurationManager.<init>(ApplicationConfigurationManager.java:146)
        at com.google.appengine.tools.development.ApplicationConfigurationManager.newWarConfigurationManager(ApplicationConfigurationManager.java:88)
        at com.google.appengine.tools.development.DevAppServerImpl.<init>(DevAppServerImpl.java:137)
        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:233)
        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)
        ... 4 more
Unable to start embedded HTTP server
com.google.gwt.core.ext.UnableToCompleteException: (see previous log entries)
        at com.google.appengine.tools.development.gwt.AppEngineLauncher.start(AppEngineLauncher.java:102)
        at com.google.gwt.dev.DevMode.doStartUpServer(DevMode.java:509)
        at com.google.gwt.dev.DevModeBase.startUp(DevModeBase.java:1093)
        at com.google.gwt.dev.DevModeBase.run(DevModeBase.java:836)
        at com.google.gwt.dev.DevMode.main(DevMode.java:311)
[ERROR] shell failed in doStartupServer method

Any ideas why? Thanks!

Answer 1

Your appengine-web.xml file is missing an entry. For hello-world you do not want to deal with concurrency (yet) so add :

<threadsafe>false</threadsafe>

to this file. You'll find it in war/META-INF/.

Once you create a concurrent application(comes much later), you can set it to true.