image showing login page not getting contents of the included servlet Classnamesimage showing login page before form processing我试图将请求从servlet转发到jsp页面，该jsp页面在页面中包含一个或多个包含的servlet，实际上将请求从servlet转发到页面不是我的问题，但是当我将它带到那时页面，缺少该页面中包含的servlet的内容...这是源代码...该类包含在页面中
package Classes;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet(name = "Classnames", urlPatterns = {"/Classnames"})
public class Classnames extends HttpServlet {
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
try{
Connection conn= ConnectionPackage.MyConnection.getConnection();
PrintWriter out = response.getWriter();
PreparedStatement ps;
ResultSet rs;
String class_name;
int class_id;
ps = conn.prepareStatement("SELECT class.class_name,class.id FROM class WHERE 1");
rs = ps.executeQuery();
while(rs.next()){
class_name = rs.getString("class_name");
class_id = rs.getInt("id");
out.println("<option value="+class_id+">"+class_name+"</option>");
}
ps.close();
rs.close();
conn.close();
}catch(Exception ex){}
}
}
然后包含所包含的servlet的页面在下面
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<meta name="author" content="David Tega">
<meta name="description" content="Cbt Training Platform">
<link rel="stylesheet" type="text/css" href="css/w3.css">
<link rel="stylesheet" type="text/css" href="css/style.css">
<link rel="stylesheet" type="text/css" href="css/responsiveness.css">
<meta name="copyright" content="copyright 2005-2020 Tech Giants"/>
<meta name="robots" content="noindex,nofollow,noarchive"/>
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Brainfield School Platform</title>
</head>
<body id="login" style="background-image: url('images/headway-5QgIuuBxKwM-unsplash.jpg'); background-size: cover;" >
<div class="w3-padding-large w3-white">
<div class="w3-container">
<p class="w3-wide w3-text-brown w3-large">Login...</p>
<p class="w3-text-red w3-small">${loginErrorMessage}</p>
</div>
<form action="StudentLogin" method="POST">
<div class="w3-row-padding">
<div class="w3-half container">
<select class="w3-select w3-border" name="class_name">
<option disabled selected>Class</option>
<jsp:include page="Classnames" flush="true"></jsp:include>
</select>
</div>
<div class="w3-half container">
<input class="w3-input w3-border" name="student_rollno" type="text" placeholder="(XXX)" maxlength="3">
</div>
<button class="w3-button w3-col w3-margin-top w3-gray w3-border w3-padding-small w3-text-white">Submit</button>
</div>
</form>
</div>
</body>
</html>
最后是在StudentLogin页面上处理表单的servlet，下面
package LoginPackage;
import java.io.IOException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
@WebServlet(name = "StudentLogin", urlPatterns = {"/StudentLogin"})
public class StudentLogin extends HttpServlet {
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
try{
Connection conn= ConnectionPackage.MyConnection.getConnection();
int roleId =6,state=1;
PreparedStatement ps;
ResultSet rs;
HttpSession ss = request.getSession(true);
String classId = request.getParameter("class_name");
String rollno = request.getParameter("student_rollno"),role,name,picture;
String id;
ps = conn.prepareStatement("SELECT students.userId,user.full_name,user.picture,roleinfo.name FROM students INNER JOIN user ON (students.userId = user.id) INNER JOIN roleinfo ON (user.roleId = roleinfo.id) WHERE students.rollno = '"+rollno+"' AND students.classId ='"+classId+"' AND user.roleId ="+roleId+" AND user.state = "+state+" ");
rs = ps.executeQuery();
if(rs.next()){
role = rs.getString("name");
name = rs.getString("full_name");
picture = rs.getString("picture");
id = rs.getString("userId");
ss.setAttribute("full_name", name);
ss.setAttribute("user_role", role);
ss.setAttribute("user_picture", picture);
ss.setAttribute("userId", id);
response.sendRedirect(request.getContextPath()+ "/StudentProfile.jsp" );
}else{
request.setAttribute("loginErrorMessage", "Incorrect Details, Try Again");
RequestDispatcher rd =request.getRequestDispatcher("StudentLogin.jsp");
rd.forward(request, response);
}
}catch(Exception ex){}
}
}
提前感谢
<jsp:include />，调用Classnames servlet的doGet方法。[使用POST方法提交表单时，您在StudentLogin servlet上使用的是RequestDispatcher.forward，因此登录JSP页面处理POST请求，<jsp:include />调用Classnames servlet的doPost方法。 >
您应该重构您的Classnames servlet，以使用doGet或doPost输出相同的结果，或者您可以使用POST-redirect-GET（并将loginErrorMessage request属性转换为请求参数）