/**
    * Logback: the reliable, generic, fast and flexible logging framework.
    * Copyright (C) 1999-2011, 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 javax.servlet.Filter;
  import javax.servlet.FilterChain;
  import javax.servlet.FilterConfig;
  import javax.servlet.ServletException;
  import javax.servlet.ServletRequest;
  import javax.servlet.ServletResponse;
  import javax.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;
    }
  
  }