java.lang.ClassNotFoundException: HelloServlet at org.apache.catalina.loader.WebappClassLoader.loadClass

Question

I have a Hello World servlet in webapps/hello/WEB-INF/class/HelloServlet.class and I registered it as below in web.xml:

<servlet>
    <servlet-name>helloServlet</servlet-name>
    <servlet-class>HelloServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>helloServlet</servlet-name>
    <url-pattern>/HelloServlet</url-pattern>
</servlet-mapping>

However, Tomcat failed to start with the below exception:

Apr 30, 2012 1:50:10 PM org.apache.catalina.core.ApplicationContext log
INFO: Marking servlet HelloServlet as unavailable
Apr 30, 2012 1:50:10 PM org.apache.catalina.core.ApplicationContext log
java.lang.ClassNotFoundException: HelloServlet
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1680)
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1526)
    at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1128)
    at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:827)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:129)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
    at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:877)
    at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process
(Http11AprProtocol.java:594)
    at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1675)
    at java.lang.Thread.run(Unknown Source)

Apr 30, 2012 1:50:10 PM org.apache.catalina.core.StandardWrapperValve invoke

How is this caused and how can I solve it?

Answer 1

The main problem is that your servlet class doesn't have a package. Declare one.

package com.example;

public class HelloServlet extends HttpServlet {

And when registering in web.xml, make sure you include the package:

<servlet-class>com.example.HelloServlet</servlet-class>

Also, your class file should be inside the /WEB-INF/classes directory, not /WEB-INF/class.

webapps/hello/WEB-INF/classes/com/example/HelloServlet.class

Answer 2

Try to keep HelloServlet class in some package(not in default package).

Answer 3

Now you can just use annotations and it will be easier:

package com.yourpackage;

import java.io.IOException;
import java.util.ResourceBundle;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Servlet implementation class HelloWorldServlet
 */
@WebServlet("/HelloWorldServlet")
public class HelloWorldServlet extends HttpServlet {

See WebServlet

Cheers!!

Answer 4

I had the same problem (I'm using old fashion servlets for "learning"), and i solved by rebuilding the maven project (in eclipse maven-->Update Project) and cleaning the project both in eclipse and tomcat. I assume the error was thrown as the class was not compiled by maven and consequently not included in the compiled packages of tomcat.