applicationservlet.java

来自「100多M的J2EE培训内容」· Java 代码 · 共 83 行

package bible.servlets;

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

public class ApplicationServlet extends HttpServlet {

  private static final int FIRST_PAGE = 1;
  private static final int LAST_PAGE = 5;

  public void service(HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException {

    ServletContext ctx = this.getServletContext();
    HttpSession session = request.getSession();
    String userName = request.getRemoteUser();
    Hashtable sessionInfo = null;

    if (session.getAttribute("sessionInfo") == null) {
      // New user. Create a Hashtable to track their
      // session state.
      sessionInfo = new Hashtable();
      sessionInfo.put("userName", userName);
      sessionInfo.put("pageNumber", new Integer(FIRST_PAGE));
      session.setAttribute("sessionInfo", sessionInfo);
      // See if the new user is already logged in by checking
      // for their sessionInfo in the servlet context.
      if (ctx.getAttribute("session_" + userName) == null) {
        // Not already logged in. Save their sessionInfo to
        // the servletContext and continue.
        ctx.setAttribute("session_" + userName, sessionInfo);
      } else {
        // Already logged in elsewhere. Invalidate this session
        // and kick this user out.
        session.invalidate();
        response.sendRedirect(response.encodeURL("/BibleServlets/Home.html"));
        return;
      }
    } else {
      // Returning user. Retrieve their state from the session.
      sessionInfo = (Hashtable) session.getAttribute("sessionInfo");
      Integer pageNumber = (Integer)sessionInfo.get("pageNumber");
      int nextPage = pageNumber.intValue();
      pageNumber = null;
      // Read the query string to determine the user's desired
      // action. Update their state in the session accordingly.
      if (request.getParameter("action").equals("next")) {
        // Go to the next page. Wrap around to the
        // first page after passing the last page.
        nextPage++;
        if (nextPage > LAST_PAGE) {
          nextPage = FIRST_PAGE;
        }
        sessionInfo.put("pageNumber", new Integer(nextPage));
        session.setAttribute("sessionInfo", sessionInfo);
        ctx.setAttribute("session_" + userName, sessionInfo);
      } else if (request.getParameter("action").equals("previous")) {
        // Go to the previous page. Wrap around to the last page
        // after passing the first page.
        nextPage--;
        if (nextPage < FIRST_PAGE) {
          nextPage = LAST_PAGE;
        }
        sessionInfo.put("pageNumber", new Integer(nextPage));
        session.setAttribute("sessionInfo", sessionInfo);
        ctx.setAttribute("session_" + userName, sessionInfo);
      } else if (request.getParameter("action").equals("logoff")) {
        // User wants to log off. Invalidate their session,
        // remove their session info from the servlet context,
        // redirect them to the home page, and then quit.
        session.invalidate();
        ctx.removeAttribute("session_" + userName);
        response.sendRedirect(response.encodeURL("/BibleServlets/Home.html"));
        return;
      }
    }
    // Forward all non-logoff requests to the PageServlet.
    request.getRequestDispatcher("PageServlet").forward(request, response);
  }

}