Debug Your App - java.lang.NoClassDefFoundError

This page shows errors where an java.lang.NoClassDefFoundError exception is thrown and how to fix them.

Table of Contents

java.lang.NoClassDefFoundError: Could not initialize class (some class name)

java.lang.NoClassDefFoundError: Could not initialize class (some class, such as gwtserver.upload.UploadAction)
        at org.apache.jsp.a_jsp._jspService(a_jsp.java:72)
        at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
        at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
        at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
        at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
        at sun.reflect.GeneratedMethodAccessor593.invoke(Unknown Source)

This exception is thrown when initialization of a class fails, unfortunately it can be quite time consuming to find the cause.

An example is that an exception is being thrown and silently ignored by the initializer or static initialization area of code in the class or a class which it relies on, preventing this class to be properly initialized.

A common cause is that log4j is being used, but not being correctly initialized. log4j is known to silently hide the error, rather than outputing it to the System.log. For example, the gwtupload serlet fails (up to version 1.0.1 anyway) with the message "INFO: Marking servlet uploadServlet as unavailable". By attempting to instantiate the class using a simple JSP test file, you can see the NoClassDefFoundError, and then looking into it further, it is caused by log4j not being initialized, due to an invalid path for the log file.

• You may see a java.security.AccessControlException or a log4j error of some type, even higher up, complaining that the log file could not be written.
• Ensure the log4j.properties file has an absolute path specified for the log file, such as /cust/myaccount/home/sample.log instead of simply sample.log
• Try instantiating the parent class of the class, and see if it can be initialized. Also check other classes that are used until you find the problem class.

java.lang.NoClassDefFoundError: Could not initialize class org.apache.struts.taglib.html.HtmlTag

java.lang.NoClassDefFoundError: Could not initialize class org.apache.struts.taglib.html.HtmlTag
	sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
	sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
	...

This exception occurs due to an inability to initialize the Struts HtmlTag tag. Depending on which tag library is used first, different struts tags may also report they cannot initialize. The first one referenced is the one that throws the exception.

The real error is that while trying to initialize, Struts tried to attach to a Logger and the Logger was not initialized, usually this is a log4j properties file error.

• You should see another java.lang.NoClassDefFoundError error higher in the log saying the class org.apache.log4j.LogManager could not be initialized.
• You should also see a java.security.AccessControlException or a log4j error of some type, even higher up, complaining that the log file could not be written.
• Fix the log error first, then restart the application. This error should no longer appear.

java.lang.NoClassDefFoundError: Could not initialize class org.apache.log4j.LogManager

SEVERE: Servlet.service() for servlet jsp threw exception
java.lang.NoClassDefFoundError: Could not initialize class org.apache.log4j.LogManager
 at org.apache.log4j.Logger.getLogger(Logger.java:85)
 at org.apache.commons.logging.impl.Log4JLogger.getLogger(Log4JLogger.java:229)
 at org.apache.commons.logging.impl.Log4JLogger.<init>(Log4JLogger.java:65)
 at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
 at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
 at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
 at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
 at org.apache.commons.logging.impl.LogFactoryImpl.newInstance(LogFactoryImpl.java:529)
 at org.apache.commons.logging.impl.LogFactoryImpl.getInstance(LogFactoryImpl.java:235)
 at org.apache.commons.logging.LogFactory.getLog(LogFactory.java:351)
 at org.apache.struts.util.MessageResources.<clinit>(MessageResources.java:57)
 at org.apache.struts.taglib.html.HtmlTag.<clinit>(HtmlTag.java:48)
 at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
 ...

This is caused by log4j not being correctly initialized.

• You should also see a java.security.AccessControlException or a log4j error of some type, even higher up, complaining that the log file could not be written.
• Fix the log error first, then restart the application. This error should no longer appear.