📄 bidservlet.java

📁 Servlet与JSP核心编程第二版代码
💻 JAVA
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package coreservlets;

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

/** Example of simplified form processing. Shows two features:
 *  <OL>
 *    <LI>Automatically filling in a bean based on the
 *        incoming request parameters.
 *    <LI>Using the same servlet both to generate the input
 *        form and to process the results. That way, when
 *        fields are omitted, the servlet can redisplay the
 *        form without making the user reenter previously
 *        entered values.
 *  </UL>
 *  <P>
 *  Taken from Core Servlets and JavaServer Pages 2nd Edition
 *  from Prentice Hall and Sun Microsystems Press,
 *  http://www.coreservlets.com/.
 *  &copy; 2003 Marty Hall; may be freely used or adapted.
 */

public class BidServlet extends HttpServlet {

  /** Try to populate a bean that represents information
   *  in the form data sent by the user. If this data is
   *  complete, show the results. If the form data is
   *  missing or incomplete, display the HTML form
   *  that gathers the data.
   */
  
  public void doGet(HttpServletRequest request,
                    HttpServletResponse response)
      throws ServletException, IOException {
    BidInfo bid = new BidInfo();
    BeanUtilities.populateBean(bid, request);
    if (bid.isComplete()) {
      // All required form data was supplied: show result.
      showBid(request, response, bid);
    } else {
      // Form data was missing or incomplete: redisplay form.
      showEntryForm(request, response, bid);
    }
  }

  /** All required data is present: show the results page. */
  
  private void showBid(HttpServletRequest request,
                       HttpServletResponse response,
                       BidInfo bid)
      throws ServletException, IOException {
    submitBid(bid);
    response.setContentType("text/html");
    PrintWriter out = response.getWriter();
    String title = "Bid Submitted";
    out.println
      (DOCTYPE +
       "<HTML>\n" +
       "<HEAD><TITLE>" + title + "</TITLE></HEAD>\n" +
       "<BODY BGCOLOR=\"#FDF5E6\"><CENTER>\n" +
       "<H1>" + title + "</H1>\n" +
       "Your bid is now active. If your bid is successful,\n" +
       "you will be notified within 24 hours of the close\n" +
       "of bidding.\n" +
       "<P>\n" +
       "<TABLE BORDER=1>\n" +
       "  <TR><TH BGCOLOR=\"BLACK\"><FONT COLOR=\"WHITE\">" +
       bid.getItemName() + "</FONT>\n" +
       "  <TR><TH>Item ID: " +
       bid.getItemID() + "\n" +
       "  <TR><TH>Name: " +
       bid.getBidderName() + "\n" +
       "  <TR><TH>Email address: " +
       bid.getEmailAddress() + "\n" +
       "  <TR><TH>Bid price: $" +
       bid.getBidPrice() + "\n" +
       "  <TR><TH>Auto-increment price: " +
       bid.isAutoIncrement() + "\n" +
       "</TABLE></CENTER></BODY></HTML>");
  }

  /** If the required data is totally missing, show a blank
   *  form. If the required data is partially missing,
   *  warn the user, fill in form fields that already have
   *  values, and prompt user for missing fields.
   */

  private void showEntryForm(HttpServletRequest request,
                      HttpServletResponse response,
                      BidInfo bid)
      throws ServletException, IOException {
    boolean isPartlyComplete = bid.isPartlyComplete();
    response.setContentType("text/html");
    PrintWriter out = response.getWriter();
    String title =
      "Welcome to Auctions-R-Us. Please Enter Bid.";
    out.println
      (DOCTYPE +
       "<HTML>\n" +
       "<HEAD><TITLE>" + title + "</TITLE></HEAD>\n" +
       "<BODY BGCOLOR=\"#FDF5E6\"><CENTER>\n" +
       "<H1>" + title + "</H1>\n" +
       warning(isPartlyComplete) +
       "<FORM>\n" +
       inputElement("Item ID", "itemID",
                    bid.getItemID(), isPartlyComplete) +
       inputElement("Item Name", "itemName",
                    bid.getItemName(), isPartlyComplete) +
       inputElement("Your Name", "bidderName",
                    bid.getBidderName(), isPartlyComplete) +
       inputElement("Your Email Address", "emailAddress",
                    bid.getEmailAddress(), isPartlyComplete) +
       inputElement("Amount Bid", "bidPrice",
                    bid.getBidPrice(), isPartlyComplete) +
       checkbox("Auto-increment bid to match other bidders?",
                "autoIncrement", bid.isAutoIncrement()) +
       "<INPUT TYPE=\"SUBMIT\" VALUE=\"Submit Bid\">\n" +
       "</CENTER></BODY></HTML>");
  }

  private void submitBid(BidInfo bid) {
    // Some application-specific code to record the bid.
    // The point is that you pass in a real object with
    // properties populated, not a bunch of strings.
  }

  private String warning(boolean isFormPartlyComplete) {
    if(isFormPartlyComplete) {
      return("<H2>Required Data Missing! " +
             "Enter and Resubmit.</H2>\n");
    } else {
      return("");
    }
  }

  /** Create a textfield for input, prefaced by a prompt.
   *  If this particular textfield is missing a value but
   *  other fields have values (i.e., a partially filled form
   *  was submitted), then add a warning telling the user that
   *  this textfield is required.
   */
  
  private String inputElement(String prompt,
                              String name,
                              String value,
                              boolean shouldPrompt) {
    String message = "";
    if (shouldPrompt && ((value == null) || value.equals(""))) {
      message = "<B>Required field!</B> ";
    }
    return(message + prompt + ": " +
           "<INPUT TYPE=\"TEXT\" NAME=\"" + name + "\"" +
           " VALUE=\"" + value + "\"><BR>\n");
  }

  private String inputElement(String prompt,
                              String name,
                              double value,
                              boolean shouldPrompt) {
    String num;
    if (value == 0.0) {
      num = "";
    } else {
      num = String.valueOf(value);
    }
    return(inputElement(prompt, name, num, shouldPrompt));
  }

  private String checkbox(String prompt,
                          String name,
                          boolean isChecked) {
    String result =
      prompt + ": " +
      "<INPUT TYPE=\"CHECKBOX\" NAME=\"" + name + "\"";
    if (isChecked) {
      result = result + " CHECKED";
    }
    result = result + "><BR>\n";
    return(result);
  }

  private final String DOCTYPE =
    "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0 " +
    "Transitional//EN\">\n";
}
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