n00b cannot get jar files to work.

How do I get jar files to work?

Learning Tomcat I have a simple "HelloServlet" class. When compiled and the
class file is inserted into the directory

/opt/tomcat/webapps/test/WEB-INF/classes/example

and the web.xml file given below is placed in

/opt/tomcat/webapps/test/WEB-INF/

and tomcat is restarted then the url

http://localhost:8080/test/hello

page reads:

Hello, world!

But if the same class is placed in a jar file and this jar file is inserted
into any of the following directories and given permissions tomcat:tomcat

/opt/tomcat/webapps/test/WEB-INF/lib
/opt/tomcat/common/lib
/opt/tomcat/shared/lib

when tomcat is restarted and the same url is addressed first there is

< Blank page >

the second time the page is refreshed there is

Status 500:
javax.servlet.ServletException: Wrapper cannot find servlet class

example.HelloServlet or a class it depends on

and the third and all subsequent times the page is refreshed there is

Status 400:
Servlet hello is not available

How do I get jar files to work? Thank you.

-- Michael

Appendix:

web.xml file:

<?xml version="1.0" encoding="ISO-8859-1"?>

<web-app xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"
version="2.4">
<servlet>
<servlet-name>hello</servlet-name>
<servlet-class>example.HelloServlet</servlet-class>
</servlet>

<servlet-mapping>
<url-pattern>/hello</url-pattern>
<servlet-name>hello</servlet-name>
</servlet-mapping>
</web-app>

HelloServlet.java:

package example;

import java.io.*;
import java.util.*;

import javax.servlet.http.*;
import javax.servlet.*;

public class HelloServlet extends HttpServlet {
public void doGet (
HttpServletRequest req,
HttpServletResponse res
) throws ServletException, IOException
{
res.setContentType("text/html");
PrintWriter pw = res.getWriter();

pw.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0
Transitional//EN\">");
pw.println();
pw.println("<head>");
pw.println("<meta http-equiv=\"Content-Type\" content=\"text/html;
charset=ISO-8859-1\">");
pw.println();
pw.println("");
pw.println();
pw.println("<title>Hello, world!</title>");
pw.println("</head>");
pw.println();
pw.println("<body bgcolor=white>");
pw.println();
pw.println("<h1>Hello, world!</h1>");
pw.println();
pw.println("</body>");
pw.close();
}

public HelloServlet() {}
}

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n00b cannot get jar files to work.

Michael Labhard

2004-05-27