（1）在有些时候我们的表单需要用户填写，但是没有填写就提交了，我们需要保留已经填写的数据然后再让用户填写没有填写的数据
（2）以一个处理拍卖竞标的servlet来实现功能：
BidInfo.java
package com.lc.ch04jingbiao;
import com.lc.ch04Biaodanshuju.ServletUtilities;
public class BidInfo {
private String itemID = "";
private String itemName = "";
private String bidderName = "";
private String emailAddress = "";
private double bidPrice = 0;
private boolean autoIncrement = false;
public String getItemName() {
return(itemName);
}
public void setItemName(String itemName) {
this.itemName = ServletUtilities.filter(itemName);
}
public String getItemID() {
return(itemID);
}
public void setItemID(String itemID) {
this.itemID = ServletUtilities.filter(itemID);
}
public String getBidderName() {
return(bidderName);
}
public void setBidderName(String bidderName) {
this.bidderName = ServletUtilities.filter(bidderName);
}
public String getEmailAddress() {
return(emailAddress);
}
public void setEmailAddress(String emailAddress) {
this.emailAddress = ServletUtilities.filter(emailAddress);
}
public double getBidPrice() {
return(bidPrice);
}
public void setBidPrice(double bidPrice) {
this.bidPrice = bidPrice;
}
public boolean isAutoIncrement() {
return(autoIncrement);
}
public void setAutoIncrement(boolean autoIncrement) {
this.autoIncrement = autoIncrement;
}
/**判断是否完成
*/
public boolean isComplete() {
return(hasValue(getItemID()) &&
hasValue(getItemName()) &&
hasValue(getBidderName()) &&
hasValue(getEmailAddress()) &&
(getBidPrice() > 0));
}
//判断是否有 没有填写的项
public boolean isPartlyComplete() {
boolean flag =
(hasValue(getItemID()) ||
hasValue(getItemName()) ||
hasValue(getBidderName()) ||
hasValue(getEmailAddress()) ||
(getBidPrice() > 0) ||
isAutoIncrement());
return(flag);
}
private boolean hasValue(String val) {
return((val != null) && (!val.equals("")));
}
}
BidServlet代码如下：
package com.lc.ch04jingbiao;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.lc.ch04Biaodanshuju.BeanUtilities;
public class BidServlet extends HttpServlet {
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>");
}
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("");
}
}
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";
}
（3）配置好servlet后，演示效果：
完全填写好表单：
如果没有完全填写表单：
提交后的结果：（提示让填写missing的Data）
ok！
时间： 2024-07-31 00:56:15