Why is Tomcat unable to show the actual stack trace?

Question

Using GWT, I have deployed my server into Tomcat. This works fine, but when GWT throws an exception, a Popup shows the client the stack trace of the exception.

In dev mode, this works fine. In Tomcat, I get the below stack trace.

Why and how do you fix this?

Unknown.Le(StackTraceCreator.java:168)
Unknown.Jd(StackTraceCreator.java:421)
Unknown.NT(Exception_FieldSerializer.java:16)
Unknown.g1(SerializerBase.java:55)
Unknown.b1(SerializerBase.java:112)
Unknown.D$(AbstractSerializationStreamReader.java:119)
Unknown.uAc(CustomException_FieldSerializer.java:39)
Unknown.uBc(ServerSideException_FieldSerializer.java:12)
Unknown.f1(SerializerBase.java:46)
Unknown._0(SerializerBase.java:92)
Unknown.D$(AbstractSerializationStreamReader.java:119)
Unknown.B_(RequestCallbackAdapter.java:216)
Unknown._o(Request.java:287)

After using @Christian Kuetbach's answer, here is what I get now:

Unknown.com_google_gwt_core_client_impl_StackTraceCreator$CollectorEmulated_$fillInStackTrace__Lcom_google_gwt_core_client_impl_StackTraceCreator$CollectorEmulated_2Ljava_lang_Throwable_2V(StackTraceCreator.java:168) Unknown.java_lang_Throwable_Throwable__Ljava_lang_String_2Ljava_lang_Throwable_2V(StackTraceCreator.java:421) Unknown.com_google_gwt_user_client_rpc_StatusCodeException_StatusCodeException__ILjava_lang_String_2V(StatusCodeException.java:35) Unknown.com_google_gwt_user_client_rpc_impl_RequestCallbackAdapter_$onResponseReceived__Lcom_google_gwt_user_client_rpc_impl_RequestCallbackAdapter_2Lcom_google_gwt_http_client_Request_2Lcom_google_gwt_http_client_Response_2V(RequestCallbackAdapter.java:209) Unknown.com_google_gwt_http_client_Request_$fireOnResponseReceived__Lcom_google_gwt_http_client_Request_2Lcom_google_gwt_http_client_RequestCallback_2V(Request.java:287) Unknown.com_google_gwt_http_client_RequestBuilder$1_onReadyStateChange__Lcom_google_gwt_xhr_client_XMLHttpRequest_2V(RequestBuilder.java:395) Unknown.anonymous(XMLHttpRequest.java:287)

Please Help!

Answer 1

It's a bit difficult to find all the information in the GWT docs, which you need to setup de-obfuscated logging, so here's the short version:

In your module file (.gwt.xml), add:

<inherits name="com.google.gwt.logging.Logging"/>
<set-property name="gwt.logging.simpleRemoteHandler" value="ENABLED" />
<set-property name="compiler.stackMode" value="emulated" />
<set-configuration-property name="compiler.emulatedStack.recordLineNumbers" 
     value="true" />

On the client side, use something like

import java.util.logging.Logger;

private static Logger rootLogger = Logger.getLogger("");
...
rootLogger.log(Level.SEVERE, "My message", e);

You don't have to create a RemoteLoggingServiceAsync instance on the client side - it's used automatically by the logger, because we specified <set-property name="gwt.logging.simpleRemoteHandler" value="ENABLED" />.

On the server side, configure the RemoteLoggingServiceImpl. You will have to tell it, where it finds the symbolMaps, which will be generated when compiling with the GWT compiler argument -extra /path/to/myExtraDir. I personally use the approach to override RemoteLoggingServiceImpl, to allow specifying the directory from web.xml's <init-param>s ^[*]

package mypackage.server;

public class ConfigurableRemoteLoggingServiceImpl extends RemoteLoggingServiceImpl {

  @Override
  public void init(final ServletConfig config) throws ServletException {
    super.init(config);

    final String symbolMapsDirectory = 
        config.getInitParameter("symbolMapsDirectory");
    setSymbolMapsDirectory(symbolMapsDirectory);
  }
}

In web.xml, register it like

<servlet>
    <servlet-name>remoteLogging</servlet-name>
    <servlet-class>mypackage.server.ConfigurableRemoteLoggingServiceImpl</servlet-class>

  <init-param>
    <param-name>symbolMapsDirectory</param-name>
    <param-value>/path/to/myExtraDir/mymodulename/symbolMaps</param-value>
  </init-param>
</servlet>
<servlet-mapping>
    <servlet-name>remoteLogging</servlet-name>
    <url-pattern>/mymodulename/remote_logging</url-pattern>
</servlet-mapping>

Replace /path/to/myExtraDir, mymodulename and mypackage with your own values, and don't forget to call the GWT compiler with the -extra argument (Note that you you don't have to use -style PRETTY or DETAILED, it also works with OBF). Keep all generated symbolMaps: Without them, deobfuscation will not work. As every new version gets a unique name automatically, you can collect them all in a safe central place when building.

^{[*] And I really, really wonder, why RemoteLoggingServiceImpl doesn't implement that itself!}