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Archive for the ‘web development’ Category

Not all Tomcat 6 classloaders must be equal

Posted by Venkatt Guhesan on July 1, 2011

Today, while doing some Grails development I came across a peculiar issue that perplexed me and I’m documenting it for all others to benefit. (Also see my other blog from today for the issue that started this journey).

Here are my specifications:

Development Machine

  • Windows-7, 64-bit
  • java version “1.6.0_24″
    Java(TM) SE Runtime Environment (build 1.6.0_24-b07)
    Java HotSpot(TM) 64-Bit Server VM (build 19.1-b02, mixed mode)
  • Grails 1.4.0.M1
  • Tomcat – apache-tomcat64-6.0.32

Local Deployment Server

  • Windows Vista, 32-bit
  • java version “1.6.0_26″
    Java(TM) SE Runtime Environment (build 1.6.0_26-b03)
    Java HotSpot(TM) Client VM (build 20.1-b02, mixed mode, sharing)
  • Grails (does not matter since I’ll be deploying a WAR)
  • Tomcat – apache-tomcat-6.0.32 (32-bit version of Tomcat)

Since the issue we are taking about deals with Grails, let’s get into he details of how I ended up with the WAR. In Grails, I issued the following command:

>grails war abcdefg.war

This creates a war file. When deployed under the 64-bit Tomcat, no issues. But when deployed under the 32-bit Tomcat. I was getting the

Jul 1, 2011 10:08:25 AM org.apache.catalina.core.StandardContext start
SEVERE: Error listenerStart

(See my previous article on how I enabled debugging to get to the root cause of the issue.)

But after some debugging, what it boiled down to was a “Class Cannot Be Found” error:

Jul 1, 2011 11:29:25 AM org.apache.catalina.core.StandardContext listenerStart
SEVERE: Error configuring application listener of class org.codehaus.groovy.grails.web.util.Log4jConfigListener
java.lang.ClassNotFoundException: org.codehaus.groovy.grails.web.util.Log4jConfigListener

In examining the war file, the JAR file named “grails-web-1.4.0.M1.jar” under the “/WEB-INF/lib” does not contain the needed “Log4jConfigListener” class under “grails-web-1.4.0.M1.jar\org\codehaus\groovy\grails\web\util\”

But clearly this class is inside this other JAR file named “grails-plugin-logging-1.4.0.M1.jar” under “\org\codehaus\groovy\grails\web\util\”.

And this identical war file works under the 64-bit Tomcat but not under the 32-bit Tomcat.

So how did I resolve the issue? I upgraded my 32-bit box to Tomcat 7.0 and this made it work. But clearly, there is an underlying issue with the class-loader under the 32-bit Tomcat 6.0.32.

Maybe someone reading this will have the answer to this issue.


Posted in Grails, Groovy, Java, Tomcat, web development | Tagged: , , , , | Leave a Comment »

Tomcat 6+: Infamous “SEVERE: Error listenerStart” message – How-To debug this error?

Posted by Venkatt Guhesan on July 1, 2011

I’m sure if you have been developing with Java and Tomcat for sometime, you are likely to run into the infamous debug error.

SEVERE: Error listenerStart

You will most likely start Googling it trying to find out what the heck is going on. And in trying to see the extended logging on what that “listenerStart” error means. After some lucky searches, you will see links asking you to drop a “” file under ‘/WEB-INF/classes’ directory inside your WAR to help debug which one of the listeners is throwing this crazy error.

Well, this advise will most likely work for you if you are developing under an earlier version of Tomcat. If you are using versions 6.0 or above then continue to read on…

In Tomcat 6 or above, the default logger is the”java.util.logging” logger and not Log4J. So if you are trying to add a “” file – this will NOT work. The Java utils logger looks for a file called “” as stated here:

So to get to the debugging details create a “” file under your”/WEB-INF/classes” folder of your WAR and you’re all set.

And now when you restart your Tomcat, you will see all of your debugging in it’s full glory!!!

Sample file:

org.apache.catalina.core.ContainerBase.[Catalina].level = INFO
org.apache.catalina.core.ContainerBase.[Catalina].handlers = java.util.logging.ConsoleHandler

and you will most likely see a “class-not-found” exception. ;-)

Look at the bright side, you’re now one step closer to the solution.

Happy coding!

Posted in Grails, Groovy, GWT, Java, Spring, Spring Framework, Tomcat, web development | Tagged: , , , , , | 13 Comments »

How-To: Turn off Firefox browser cache during development

Posted by Venkatt Guhesan on June 22, 2011

Sometimes (when your are developing) you may want to force fetching all content fresh all the time including images, resources such as style sheet etc. To facilitate this you can do the following:

  1. Open a new window or tab in Firefox.
  2. Type about:config in the address bar.
  3. Search for “cache” in the search bar and look for network.http.use-cache in the filtered results.
  4. Double-click it will toggle it from “true” to “false”. Default should be “true”.

And you’re all set.

Sometime you want to force the cache on one particular page\request. You can do that by holding the “Ctrl” key while clicking reload or F5.


Posted in web development | Tagged: , | 2 Comments »

Add custom jars under “\WEB-INF\lib” in a Maven project

Posted by Venkatt Guhesan on October 2, 2010

The answer is a lot simpler than you think. But before we explore the answer, I should warn you that this approach is not what is recommended by Maven. Maven builds upon consistency and structure and this process goes away from that methodology. In Maven, you can take each of your jars\libraries and add them to your local repository and then include them as needed in your projects. If you want to go the proper route here’s how you do it. This keeps a consistent version in all your projects and can allow you to gracefully update the library as new versions become available.

But if you still want to go ahead and add these custom jars in your project then follow these steps:

1. Create a “lib” folder under your project like this: “\src\main\webapp\WEB-INF\lib”
2. Copy needed “jars” etc that you want included inside your WAR bundle folder.
3. Invoke your maven build as you normally do. I use “mvn install”, which creates builds the war file.

If you examine the WAR file, your jars that you included in step-1 and step-2 will be there.

Posted in Java, Maven, web development | Tagged: , , , | 3 Comments »


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