SERVLET如何从上一个页面取得参数

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
  <TITLE>A Sample FORM using POST</TITLE>
</HEAD>
<BODY BGCOLOR="#FDF5E6">
<H1 ALIGN="CENTER">A Sample FORM using POST</H1>

<FORM ACTION="servlet/ShowParameters" 
      METHOD="get">
  Item Number: <INPUT TYPE="TEXT" NAME="itemNum"><BR>
  Quantity: <INPUT TYPE="TEXT" NAME="quantity"><BR>
  Price Each: <INPUT TYPE="TEXT" NAME="price" VALUE="$"><BR>
  <HR>
  First Name: <INPUT TYPE="TEXT" NAME="firstName"><BR>
  Last Name: <INPUT TYPE="TEXT" NAME="lastName"><BR>
  Middle Initial: <INPUT TYPE="TEXT" NAME="initial"><BR>
  Shipping Address:
  <TEXTAREA NAME="address" ROWS=3 COLS=40></TEXTAREA><BR>
  Credit Card:<BR>
  &nbsp;&nbsp;<INPUT TYPE="RADIO" NAME="cardType"
                     VALUE="Visa">Visa<BR>
  &nbsp;&nbsp;<INPUT TYPE="RADIO" NAME="cardType"
                     VALUE="Master Card">Master Card<BR>
  &nbsp;&nbsp;<INPUT TYPE="RADIO" NAME="cardType"
                     VALUE="Amex">American Express<BR>
  &nbsp;&nbsp;<INPUT TYPE="RADIO" NAME="cardType"
                     VALUE="Discover">Discover<BR>
  &nbsp;&nbsp;<INPUT TYPE="RADIO" NAME="cardType"
                     VALUE="Java SmartCard">Java SmartCard<BR>
  Credit Card Number: 
  <INPUT TYPE="PASSWORD" NAME="cardNum"><BR>
  Repeat Credit Card Number:
  <INPUT TYPE="PASSWORD" NAME="cardNum"><BR><BR>
  <CENTER>
    <INPUT TYPE="SUBMIT" VALUE="Submit Order">
  </CENTER>
</FORM>

</BODY>
</HTML>

package com.bjsxt;

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

//获取所有的参数

public class ShowParameters extends HttpServlet {
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setContentType("text/html;charset=gb2312");
		PrintWriter out = response.getWriter();
		String title = "Reading All Request Parameters";
		out.println("<html><head><title>读取所有参数</title></head>"
				+ "<BODY BGCOLOR='#FDF5E6'>\n" + "<H1 ALIGN=CENTER>" + title
				+ "</H1>\n" + "<TABLE BORDER=1 ALIGN=CENTER>\n"
				+ "<TR BGCOLOR=\"#FFAD00\">\n"
				+ "<TH>Parameter Name<TH>Parameter Value(s)");
		Enumeration paramNames = request.getParameterNames();
		while (paramNames.hasMoreElements()) {
			String paramName = (String) paramNames.nextElement();
			out.print("<TR><TD>" + paramName + "\n<TD>");
			String[] paramValues = request.getParameterValues(paramName);
			if (paramValues.length == 1) {
				String paramValue = paramValues[0];
				if (paramValue.length() == 0)
					out.println("<I>No Value</I>");
				else
					out.println(paramValue);
			} else {
				out.println("<UL>");
				for (int i = 0; i < paramValues.length; i++) {
					out.println("<LI>" + paramValues[i]);
				}
				out.println("</UL>");
			}
		}
		out.println("</TABLE>\n</BODY></HTML>");
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		doGet(request, response);
	}
}

我们要注意
      Credit Card Number:
     <INPUT TYPE="PASSWORD" NAME="cardNum"><BR>
      Repeat Credit Card Number:
     <INPUT TYPE="PASSWORD" NAME="cardNum"><BR><BR>
这两句代码 name属性一样
那么我们就不能简单的用request.getParameter()了。
先用Enumeration paramNames = request.getParameterNames();获得所有的name,一个枚举
然后迭代此枚举,如果表单中的文本框什么都没填传过来的是""而不是null

SERVLET如何从上一个页面取得参数

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