package com.atlassian.plugin.refimpl.servlet;
   
   import org.slf4j.Logger;
   import org.slf4j.LoggerFactory;
   
   import javax.servlet.ServletException;
   import javax.servlet.ServletRequest;
   import javax.servlet.ServletResponse;
   import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  import java.io.IOException;
  import java.util.Enumeration;
  
  /**
   * NoOpServlet is a dummy servlet used only to provide a servlet mapping for url patterns that don't have any. This is
   * necessary as some application servers like WebSphere 6.1.0.5 returns a 404 if there are no mapped servlet before
   * applying filters to the request which could potentially change the URL mapped to a valid servlet. For example, the
   * {@code URLRewriter} filter does this. Hence this dummy servlet should never handle any requests.
   * <p>
   * If this servlet receives a request, it will simply log all relevant information from the request that may be of help
   * in determining why the request was received, as this would not be the desired result.
   * </p>
   *
   * @since 2.3.6
   */
  public class NoOpServlet extends HttpServlet {
      private static final Logger log = LoggerFactory.getLogger(NoOpServlet.class);
      private static final String RECEIVED_UNEXPECTED_REQUEST = "NoOpServlet received an unexpected request.";
      private static final String UNABLE_TO_HANDLE_REQUEST =
              "Unable to handle request. Request is not a HttpServletRequest";
  
      public void service(ServletRequest servletRequest, ServletResponse servletResponse)
              throws ServletException, IOException {
          log.warn(RECEIVED_UNEXPECTED_REQUEST);
  
          if (!(servletRequest instanceof HttpServletRequest && servletResponse instanceof HttpServletResponse)) {
              log.error(UNABLE_TO_HANDLE_REQUEST);
              return;
          }
          HttpServletRequest request = (HttpServletRequest) servletRequest;
          HttpServletResponse response = (HttpServletResponse) servletResponse;
  
          //log information that may help in finding out why the request came here
          logRequestInformation(request);
  
          //Let the user know that there is some error
          response.sendError(404, RECEIVED_UNEXPECTED_REQUEST + " More information is available in the log file.");
      }
  
      /**
       * Logs relevant information about the request such as the request URL and the query string
       *
       * @param request request to log information about
       */
      private void logRequestInformation(HttpServletRequest request) {
          try {
              log.warn("Request Information");
              log.warn("- Request URL: " + request.getRequestURL());
              log.warn("- Query String: " + (request.getQueryString() == null ? "" : request.getQueryString()));
  
              log.warn("Request Attributes");
              Enumeration attributeNames = request.getAttributeNames();
              while (attributeNames.hasMoreElements()) {
                  String name = (String) attributeNames.nextElement();
                  Object attribute = request.getAttribute(name);
                  log.warn("- " + name + ": " + (attribute == null ? "null" : attribute.toString()));
              }
          } catch (Throwable t) {
              log.error("Error rendering logging information" + t);
          }
      }
  }