Example 7.34 Dispatcher View Controller Servlet

public class Controller extends HttpServlet {

  /** Processes requests for both HTTP 
    * <code>GET</code> and <code>POST</code> methods.
    * @param request servlet request
    * @param response servlet response
    */
  protected void processRequest(HttpServletRequest 
    request, HttpServletResponse response)
    throws ServletException, java.io.IOException {
    String nextview;
    try {
      LogManager.recordStrategy(request, 
        "Dispatcher View", 
        " Servlet Front Strategy; " + 
    "JSP View Strategy; Custom tag helper Strategy");
      LogManager.logMessage(request, getSignature(), 
        "Process incoming request. ");

      // Use a helper object to gather parameter 
      // specific information.
      RequestHelper helper = new 
          RequestHelper(request, response);
      LogManager.logMessage(request, 
        getSignature(), " Authenticate user");

      Authenticator auth = new BasicAuthenticator();
      auth.authenticate(helper);

      //This is an oversimplification for the sake of 
      // simplicity. Typically, there will be a 
      // mapping from logical name to resource name at 
      // this point
      LogManager.logMessage(request, getSignature(), 
        "Getting nextview");
      nextview = request.getParameter("nextview");

      LogManager.logMessage(request, getSignature(), 
        "Dispatching to view: " + nextview);
    }
    catch (Exception e) {
      LogManager.logMessage(
        "Handle exception appropriately", 
        e.getMessage() );
      /** ApplicationResources provides a simple API 
        * for retrieving constants and other 
        * preconfigured values**/
      nextview = ApplicationResources.getInstance().
          getErrorPage(e);
    }
    dispatch(request, response, nextview);
  }

  /** Handles the HTTP <code>GET</code> method.
    * @param request servlet request
    * @param response servlet response
    */
  protected void doGet(HttpServletRequest request, 
    HttpServletResponse response)
  throws ServletException, java.io.IOException {
    processRequest(request, response);
 }

  /** Handles the HTTP <code>POST</code> method.
    * @param request servlet request
    * @param response servlet response
    */
  protected void doPost(HttpServletRequest request, 
    HttpServletResponse response)
  throws ServletException, java.io.IOException {
    processRequest(request, response);
  }

  /** Returns a short description of the servlet. */
  public String getServletInfo(){
      return getSignature();
  }

  public void init(ServletConfig config) throws 
    ServletException {
    super.init(config);
  }

  public void destroy() { }

  /**
    * dispatcher method
    */
  protected void dispatch(HttpServletRequest request,
    HttpServletResponse response, String page) 
    throws javax.servlet.ServletException, 
    java.io.IOException {
        RequestDispatcher dispatcher = 
          getServletContext(). 
            getRequestDispatcher(page);
        dispatcher.forward(request, response);
  }

  private String getSignature()  {
    return "DispatcherView-Controller"; 
  }
}