/**
    * Logback: the reliable, generic, fast and flexible logging framework.
    * Copyright (C) 1999-2015, QOS.ch. All rights reserved.
    *
    * This program and the accompanying materials are dual-licensed under
    * either the terms of the Eclipse Public License v1.0 as published by
    * the Eclipse Foundation
    *
    *   or (per the licensee's choosing)
   *
   * under the terms of the GNU Lesser General Public License version 2.1
   * as published by the Free Software Foundation.
   */
  package chapters.mdc;
  
  import java.io.IOException;
  import java.security.Principal;
  
  import jakarta.servlet.Filter;
  import jakarta.servlet.FilterChain;
  import jakarta.servlet.FilterConfig;
  import jakarta.servlet.ServletException;
  import jakarta.servlet.ServletRequest;
  import jakarta.servlet.ServletResponse;
  import jakarta.servlet.http.HttpServletRequest;
  
  import org.slf4j.MDC;
  
  /**
   * A simple servlet filter that puts the username
   * found either in the Principal.
   * 
   * <p> The value is removed from the MDC once the request has been
   * fully processed.
   *
   * @author S&eacute;bastien Pennec
   */
  public class UserServletFilter implements Filter {
  
      private final String USER_KEY = "username";
  
      public void destroy() {
      }
  
      public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
  
          boolean successfulRegistration = false;
          HttpServletRequest req = (HttpServletRequest) request;
          Principal principal = req.getUserPrincipal();
          // Please note that we also could have used a cookie to
          // retrieve the user name
  
          if (principal != null) {
              String username = principal.getName();
              successfulRegistration = registerUsername(username);
          }
  
          try {
              chain.doFilter(request, response);
          } finally {
              if (successfulRegistration) {
                  MDC.remove(USER_KEY);
              }
          }
      }
  
      public void init(FilterConfig arg0) throws ServletException {
      }
  
      /**
       * Register the user in the MDC under USER_KEY.
       * 
       * @param username
       * @return true id the user can be successfully registered
       */
      private boolean registerUsername(String username) {
          if (username != null && username.trim().length() > 0) {
              MDC.put(USER_KEY, username);
              return true;
          }
          return false;
      }
  
  }