我试图从jsp获取一个值到sevlet.First变量值由session setArribute（），getAttribute（）获取然后我需要将该特定变量从jsp传递给servlet但是我得到的值为null变量
下面我将分享我的代码，任何人都可以知道如何解决这个问题？
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@page import="java.sql.*"%>
<html>
<head>
<title>Welcome to survey</title>
</head>
<body>
<%
ResultSet rset;
String sur_id = request.getParameter("surveyid");
session.setAttribute( "surveyid", sur_id );
int new_survey_id = Integer.parseInt(sur_id);
if (request.getParameter("surveyid") == null) {
out.println("Please enter your name.");
} else {
out.println("Hello <b>"+request.getParameter("surveyid")+"</b>!");
}
Class.forName("com.mysql.jdbc.Driver").newInstance();
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/surveysample", "root", "root");
String query = "select * from surveydetail where surveyid ="+ new_survey_id ;
Statement stmt = con.createStatement();
rset = stmt.executeQuery(query);
while(rset.next()){
// out.println(rset.getString(1));
// out.println(rset.getString(2));
// out.println(rset.getString(3));
// out.println(rset.getString(4));
%>
<table border="3">
<tr><td>Survey_Id</td><td><%=rset.getString(1)%></td></tr>
<tr><td>Family name</td><td><%=rset.getString(2)%></td></tr>
<tr><td>First name</td><td><%=rset.getString(3)%></td></tr>
<tr><td>Middle name</td><td><%=rset.getString(4)%></td></tr>
<tr><td>gender</td><td><%=rset.getString(5)%></td></tr>
<tr><td>dat of birth</td><td><%=rset.getString(6)%></td></tr>
<tr><td>income</td><td><%=rset.getString(7)%></td></tr>
<tr><td>complete address</td><td><%=rset.getString(8)%></td></tr>
<tr><td>coordinates</td><td><%=rset.getString(9)%></td></tr>
<tr><td>mobile number</td><td><%=rset.getString(10)%></td></tr>
<tr><td>email address</td><td><%=rset.getString(11)%></td></tr>
<tr><td>present Internet provider</td><td><%=rset.getString(12)%></td></tr>
<tr><td>comments</td><td><%=rset.getString(13)%></td></tr>
<tr><td>remarks</td><td><%=rset.getString(14)%></td></tr>
<br>
<form>
<table>
<tr><td><input type="button" value="edit" onclick="javascript:document.forms[0].action = 'EditSurvey.jsp'; document.forms[0].submit();"></td>            
<td><input type="button" value="delete"></td>            
<td><input type="button" value="print"></td>            
<td><input type="button" value="send mail"></td>            
</tr>
</table>
</form>
</table>
<%
}
%>
</body>
</html>
从上面的代码中我将会话变量设置为surveyid 我可以从下面的代码中得到它。它正常工作
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Edit survey</title>
</head>
<body>
<%
ResultSet resultSet;
String surveyId = (String) session.getAttribute("surveyid");
out.println("check"+surveyId);
request.setAttribute("surveyid", surveyId);
Class.forName("com.mysql.jdbc.Driver").newInstance();
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/surveysample", "root", "root");
String query = "select * from surveydetail where surveyid ="+ surveyId ;
Statement stmt = con.createStatement();
ResultSet rset = stmt.executeQuery(query);
while(rset.next()){
%>
<form name="Editsurveyform" method="post" action="EditSurvey">
<table>
<tr><td>Family name:</td><td><input type="text" name="familyName" value='<%=rset.getString(2)%>'></td></tr>
<tr><td>First name:</td><td><input type="text" name="firstName" value='<%=rset.getString(3)%>'></td></tr>
<tr><td>Middle name:</td><td><input type="text" name="middleName" value='<%=rset.getString(4)%>'></td></tr>
<tr><td>Gender:</td>
<td>
<%
if(rset.getString(5).equals("male")){
%>
<input type="radio" name="sex" value="male" checked>Male
<input type="radio" name="sex" value="female">Female
<%}
else{
%>
<input type="radio" name="sex" value="male">Male
<input type="radio" name="sex" value="female" checked>Female
<%
}
%>
</td>
</tr>
<tr><td>Birthday:</td><td><input type="date" name="dob" value='<%=rset.getString(6)%>'></td></tr>
<tr><td>Income : A?B?C?D?</td><td><input type="text" name="income" value='<%=rset.getString(7)%>'></td></tr>
<tr><td>Complete Address:</td><td><input type="text" name="address" value='<%=rset.getString(8)%>'></td></tr>
<tr><td>Coordinates:</td><td><input type="text" name="coordinates" value='<%=rset.getString(9)%>'></td></tr>
<tr><td>Mobile number:</td><td><input type="tel" name="mobileno" value='<%=rset.getString(10)%>'></td></tr>
<tr><td>Email Address:</td><td><input type="email" name="email" value='<%=rset.getString(11)%>'></td></tr>
<tr><td>Present internet provider:</td><td><input type="text" name="iprovider" value='<%=rset.getString(12)%>'></td></tr>
<tr><td>Positive comments with present provider:</td><td><textarea name="comments" cols="40" rows="5"><%=rset.getString(13)%></textarea></td></tr>
<tr><td>Negative remarks with present provider:</td><td><textarea name="remarks" cols="40" rows="5"><%=rset.getString(14)%></textarea></td></tr>
<tr><td><input type="submit" name="editsurvey" value="update survey details"></td><td><input type="reset" name="cancel" value="cancel"></td></tr>
</table>
</form>
<%}
//response.sendRedirect("EditSurvey?surveyId="+surveyId);
%>
</body>
</html>
但我在下面的java中遇到了问题
package com.survey;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
/**
* Created by rajee on 2/18/15.
*/
public class EditSurvey extends HttpServlet {
public String familyName;
public String firstName;
public String middlename;
public String gender;
public String dateOfBirth;
public String income;
public String completeAddress;
public String coordinates;
public String mobileno;
public String emailAddress;
public String presentIP;
public String comment;
public String remark;
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String surveyId = (String) request.getAttribute("surveyid");
System.out.println(surveyId);
familyName = request.getParameter("familyName");
firstName = request.getParameter("firstName");
middlename = request.getParameter("middleName");
gender = request.getParameter("sex");
dateOfBirth = request.getParameter("dob");
income = request.getParameter("income");
completeAddress = request.getParameter("address");
coordinates = request.getParameter("coordinates");
mobileno = request.getParameter("mobileno");
emailAddress = request.getParameter("email");
presentIP = request.getParameter("iprovider");
comment = request.getParameter("comments");
remark = request.getParameter("remarks");
System.out.println(familyName);
System.out.println(firstName);
System.out.println(middlename);
System.out.println(gender);
System.out.println(dateOfBirth);
System.out.println(income);
System.out.println(completeAddress);
System.out.println(coordinates);
System.out.println(mobileno);
System.out.println(emailAddress);
System.out.println(presentIP);
System.out.println(comment);
System.out.println(remark);
response.setContentType("text/html");
PrintWriter pw = response.getWriter();
Connection conn=null;
String url="jdbc:mysql://localhost:3306/";
String dbName="surveysample";
String driver="com.mysql.jdbc.Driver";
//String dbUserName="root";
//String dbPassword="root";
// try{
//
//
// Class.forName(driver).newInstance();
// conn = DriverManager.getConnection(url + dbName, "root", "root");
// PreparedStatement pst =(PreparedStatement) conn.prepareStatement("insert into surveysample.surveydetail(familyname,firstname,middlename,gender,dateofbirth,income,complete_address,coordinates,mobilenumber,emailaddress,presentiprovider,comments,remarks) values (?,?,?,?,?,?,?,?,?,?,?,?,?)");//try2 is the name of the table
//
// pst.setString(1,familyName);
// pst.setString(2,firstName);
// pst.setString(3,middlename);
// pst.setString(4,gender);
// pst.setString(5,dateOfBirth);
// pst.setString(6,income);
// pst.setString(7,completeAddress);
// pst.setString(8,coordinates);
// pst.setString(9,mobileno);
// pst.setString(10,emailAddress);
// pst.setString(11,presentIP);
// pst.setString(12,comment);
// pst.setString(13,remark);
//
//
// int i = pst.executeUpdate();
// //conn.commit();
// String msg=" ";
// if(i!=0){
// msg="Record has been inserted";
// pw.println("<font size='6' color=blue>" + msg + "</font>");
//
//
// }
// else{
// msg="failed to insert the data";
// pw.println("<font size='6' color=blue>" + msg + "</font>");
// }
// pst.close();
// }
// catch (Exception e){
// pw.println(e);
// }
//
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
}
代码
答案 0 :(得分：0)
如果你的问题是surveyId为空是servlet，这是正常的，因为你试图从请求中获取它：
String surveyId = (String) request.getAttribute("surveyid");
当你把它放在会话中时，你应该从那里阅读：
String surveyId = (String) request.getSession().getAttribute("surveyid");
答案 1 :(得分：0)
您可以在servlet中尝试以下代码：
HttpSession session = request.getSession(false);
String surveyId = (String) session.getAttribute("surveyid");
如果会话对象已存在，则此方法request.getSession(false)将不会创建新会话。它只会返回旧的会话对象，否则它将返回null。