package com.example;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class JWhichServlet extends HttpServlet {
    public void service(HttpServletRequest req,
                        HttpServletResponse resp)
                throws ServletException, IOException {
        PrintWriter pw = new PrintWriter(resp.getOutputStream());
        int idx = req.getRequestURI().lastIndexOf("/");
        if (idx < 0) {
            pw.printf("Nothing to do for: %s", req.getRequestURI());
        }
        else {
            java.net.URL classUrl = null;
            String className = req.getRequestURI().substring(idx + 1);
            if (className != null) {
                // try to find a normal file, such as log4j.properties
                String clsName = "/" + className;
                classUrl = this.getClass().getResource(clsName);

                if (classUrl == null) {
                    // try to find a class
                    clsName = clsName.replace('.', '/') + ".class";
                    classUrl = this.getClass().getResource(clsName);
                }
            }

            if (classUrl == null) {
                pw.printf("'%s' not found", className);
            }
            else {
                pw.printf("'%s' found in: %s",
                          className,
                          classUrl.getFile());
            }
        }
        pw.close();
    }
}

<servlet>
    <servlet-name>jwhich</servlet-name>
    <servlet-class>com.example.JWhich</servlet-class>
</servlet>

<servlet-mapping>
    <servlet-name>jwhich</servlet-name>
    <url-pattern>/jwhich/*</url-pattern>
</servlet-mapping>

http://mydomain.com/jwhich/com.example.SomeClass
http://mydomain.com/jwhich/log4j.properties