votecounter2.java

对于初学者来说..是应该理解下了..我说的是JSP哦

// VoteCounter2.java
// This servlet processes the ballot form, returning a 
//  page asking for a new vote if no vote was made on the
//  ballot. For legitimate ballots, the vote is added to
//  the current totals, and those totals are presented to
//  the user in a return page.
// This servlet uses session tracking rather than cookies.
// The voting data file, votesdat.dat, is stored on the Web server.

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

public class VoteCounter2 extends HttpServlet {
    PrintWriter servletOut;
    int index;
    public void doPost(HttpServletRequest request,
                       HttpServletResponse response)
throws ServletException, IOException {
        HttpSession mySession = null;
        int votes[] = null;
        String vote;
        File votesdat = new File("votesdat.dat");
        String candidates[] = {"Daren Dogman", "Timmy Taildragger",
                               "Don Dogpile"};

// Check to see if there was a vote on the form

        vote = request.getParameter("vote");
        if (vote == null) {  // There was no vote

// Create the return page

            makeHeader(response);
            servletOut.println(
                "You submitted a ballot with no vote marked");
            servletOut.println(
                "Please mark the ballot and resubmit");
        }  // end of if vote == null) ...
        else {  // There was a vote
                  
// Check to see if this client voted before

            if (!votedBefore(mySession, request)) {

// No previous vote, so read the file (if it exists)

// Synchronize a block for the file access

                synchronized(this) {

                    if (votesdat.exists()) {
                        ObjectInputStream indat = 
                            new ObjectInputStream(
                            new FileInputStream(votesdat));

// We need try/catch here because readObject may throw the
//  ClassNotFoundException

                        try {
                            votes = (int []) indat.readObject();
                        }  
                        catch(ClassNotFoundException problem) {
problem.printStackTrace();
                        }
                        indat.close(); 
                    }  // end of if (votesdat...

// If the file does not exist (this is the first vote), create the 
//  votes array

                    else
                        votes = new int[3];

// Add the new vote of the response to the votes array

                    if (vote.equals("Dogman")) 
                        votes[0]++;
                    else if (vote.equals("Taildragger"))
                        votes[1]++;
                    else votes[2]++;

// Write updated votes array to disk

                    ObjectOutputStream outdat = 
                        new ObjectOutputStream(
                        new FileOutputStream(votesdat));
                    outdat.writeObject(votes);
                    outdat.flush();
                    outdat.close();

                }  //** end of the synchronized block

// Create a session object and set a value to indicate a vote

                mySession = request.getSession(true);
                mySession.putValue("iVoted", "true");
                
// Write a response message

                makeHeader(response);
                servletOut.println("Your vote has been received");
                servletOut.println(
                    "<br/> <br/> Current Voting Totals:<br/>");

// Create the total votes return information 
      
                for (index = 0; index < 3; index++) {
                    servletOut.println("<br/>");
servletOut.print(candidates[index]);
                    servletOut.print(": ");
                    servletOut.println(votes[index]);
                }
            }  // end of if (!votedBefore( ...
            else {  // The client voted before

 // Write a response message

                makeHeader(response);
                servletOut.println(
                    "Your vote is illegal - you already voted!");
            }  // end of else
        }  // end of else (there was a vote)
      
        servletOut.println("</body> </html>");
        servletOut.close();  
        
    }  // end of doPost
//----------------------------------------------------------------
// Method votedBefore - return true if the client voted before;
//  false otherwise

    boolean votedBefore(
                HttpSession mySession, HttpServletRequest request) {
  
// Get the session object, if there is one

        mySession = request.getSession(false);

// If there was no session, the vote must be okay

        if (mySession == null) 
            return false;
        else { // there was a session
            String names [] = mySession.getValueNames();
            for (index = 0; index < names.length; index++) {
                if (names[index].equals("iVoted") && 
                 mySession.getValue(names[index]).equals("true"))
                    return true;
            
            }  // end of for (index = 0; ...  
     
            return false;
        }  // end of else      
}  // end of votedBefore
//----------------------------------------------------------------
// Method makeHeader -
// get the writer and produce the response header
    void makeHeader(HttpServletResponse response) 
             throws IOException {

// Set content type for response and get a writer

        response.setContentType("text/html"); 
        servletOut = response.getWriter();
    
// Write the response document head and the message

        servletOut.println("<html><head>");
        servletOut.println(
            "<title> Return message - </title></head><body>");
    }  // end of makeHeader
   }  // end of VoteCounter2