将变量从jsp传递给servlet时获取null值

Question

I am trying to get a value from jsp to sevlet.First the variable value is taken by session setArribute(), getAttribute() then I need to pass that particular variable from jsp to servlet but I am getting null value for that variable. 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但我得到该变量的null值。

Here below I am sharing my code, can anyone findout how can I solve this issue? 我在下面分享我的代码，任何人都可以找到我如何解决这个问题？

 <%@ 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>&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp <td><input type="button" value="delete"></td>&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp <td><input type="button" value="print"></td>&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp <td><input type="button" value="send mail"></td>&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp </tr> </table> </form> </table> <% } %> </body> </html>

from the above code I have set the session variable as surveyid and I can get it from the below code.It is working properly 从上面的代码我已经将session变量设置为surveyid，我可以从下面的代码中获取它。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>

But I encounter the problem in below java 但是我遇到了java下面的问题

 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 { } }

code 码

Answer 1

If your problem is for surveyId being null is servlet, it is normal because you try to get it from request : 如果您的问题是surveyId为null是servlet，这是正常的，因为您尝试从请求中获取它：

String surveyId = (String) request.getAttribute("surveyid");

As you put it in session , you should read it from there : 当你把它放在会话中时 ，你应该从那里阅读它：

String surveyId = (String) request.getSession().getAttribute("surveyid");

Answer 2

You can try below code in your servlet as : 您可以在servlet中尝试以下代码：

HttpSession session = request.getSession(false); 
String surveyId = (String) session.getAttribute("surveyid");

this method request.getSession(false) will not create new session if session object is already exists. 如果会话对象已存在，则此方法request.getSession(false)将不会创建新会话。 it will simply return old session object if its there otherwise it will return null. 它只会返回旧的会话对象，否则它将返回null。

将变量从jsp传递给servlet时获取null值

问题描述

2 个解决方案

解决方案1
0 2015-02-18 07:22:25

解决方案2
0 2015-02-18 07:26:46

将变量从jsp传递给servlet时获取null值

问题描述

2 个解决方案

解决方案1 0 2015-02-18 07:22:25

解决方案2 0 2015-02-18 07:26:46

解决方案1
0 2015-02-18 07:22:25

解决方案2
0 2015-02-18 07:26:46