文章/答案/技术大牛

发布

社区首页 >问答首页 >使用servlet使用id打开jsp编辑页

问使用servlet使用id打开jsp编辑页
EN

Stack Overflow用户

提问于 2021-08-01 01:03:32

回答 1查看 764关注 0票数 1

我对使用Servlets和JSP相当陌生，我正在尝试获得一个JSP页面，该页面列出所有用户，并根据用户id重定向到编辑表单jsp，列出所有用户的JSP页面使用迭代器从我的JDBC表中显示数据，但我似乎不知道如何为每个用户的编辑链接分别分配一个值，这样它就可以用该用户的数据加载编辑表单，您的帮助将不胜感激。

这里我的jsp页面的当前代码列出了所有的学生。

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1" import="java.util.*" import="model.Student"%>

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, intial-scale=1 shink-to-fit=yes">

    <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/css/bootstrap.min.css" 
    integrity="sha384-..." crossorigin="anonymous">
</head>
<body>
    <nav class="navbar navbar-dark bg-primary pd-8">
         <a class="navbar-brand">&nbsp;&nbsp;&nbsp;&nbsp;...University</a>
    </nav>
    <div class="container-fluid">
    <div class="container">

            <div class="form container-fluid p-4">
               <a href="<%=request.getContextPath()%>/new" class="btn btn-success" >Add
                    Student</a>
            </div>
            <br>
            
            <!--Assigning ArrayList object containing student data to the local object -->
            <% ArrayList<Student> studentList = (ArrayList) request.getAttribute("listStudents"); %> 
            <table class="table table-bordered">
            
                <thead>
                    <tr>
                        <th>ID</th>
                        <th>Name</th>
                        <th>Email</th>
                        <th>Actions</th>
                    </tr>
                </thead>
                <tbody>
                    <!-- data from table displayed using iterator-->
                    <%
                     if(request.getAttribute("listStudents") != null)  {
                            Iterator<Student> iterator = studentList.iterator();
                            while(iterator.hasNext()) {
                                Student studentDetails = iterator.next();
                    %>
                        <tr><td><%=studentDetails.getId()%></td>
                            <td><%=studentDetails.getName()%></td>
                            <td><%=studentDetails.getEmail()%></td>
                            <td><a href="<%=request.getContextPath()%>/edit?id=<%=studentDetails.getId()%>">Update</a> <!-- id assigned to edit link-->
                                &nbsp;&nbsp;&nbsp;&nbsp; <a href="<%=request.getContextPath()%>/delete?id=<%=studentDetails.getId()%>">Delete</a></td>  <!-- id assigned to delete link-->
                        </tr>
                    <% 
                            }
                     }
                    %>
                </tbody>
                
            </table>
            </div>
        </div>
        
    </body>
</html>

然后将id值分配给servlet中的一个值，该值用于在调用编辑时从表中选择特定的学生。

以下是我的servlet代码的一部分：

import java.io.IOException;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.List;
import jakarta.servlet.RequestDispatcher;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServlet;
import dao.StudentDao;
import model.Student;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

public class StudentServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private StudentDao studentDao;

    public StudentServlet() {
        this.studentDao = new StudentDao();
    }

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

    
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String sPath = request.getServletPath();
        //switch statement to call appropriate method
        switch (sPath) {
            case "/new":
                try {
                    showNewForm(request, response);
                } catch (ServletException | IOException e) {
                    e.printStackTrace();
                }
                break;
            case "/insert":
                try {
                    insertStudent(request, response);
                } catch (SQLException | IOException e) {
                    e.printStackTrace();
                } 
                break;
            case "/delete":
                try {
                    deleteStudent(request, response);
                } catch (SQLException | IOException e) {
                    e.printStackTrace();
                }
                break;
            case "/update":
                try {
                    updateStudent(request, response);
                } catch (SQLException | IOException e) {
                    e.printStackTrace();
                }
                break;
            case "/edit":
                try {
                    editStudent(request, response);
                } catch (ServletException | IOException e) {
                    e.printStackTrace();
                }
                break;
            default:
                try {
                    listAllStudents(request, response); //home page = .../week04/StudentServlet
                } catch (ServletException | IOException | SQLException e) {
                    e.printStackTrace();
                } 
                break; 
            } 
    }

    private void editStudent(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException {
        int id = Integer.parseInt(request.getParameter("id"));
        Student currentStudent = studentDao.selectStudent(id);
        System.out.println(currentStudent);
        RequestDispatcher dispatch = request.getRequestDispatcher("student-form.jsp");
        request.setAttribute("student", currentStudent); 
        dispatch.forward(request, response);
    }

    private void listAllStudents(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException, SQLException {
        List<Student> allStudents = studentDao.selectAllStudents();
        request.setAttribute("listStudents", allStudents);
        RequestDispatcher dispatch = request.getRequestDispatcher("student-list.jsp");
        dispatch.forward(request, response);
    }
}

这是我的DAO，以防我没有正确配置它：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import model.Student;

public class StudentDao {
    private String jdbcURL = "jdbc:mysql://localhost:3308/xyzuniversity";
    private String jdbcUsername = "User";
    private String jdbcPassword = "password";
    
    
    private static final String SELECT_STUDENT_ID = "SELECT name, email FROM student WHERE id =?";

    protected Connection getConnection() {
    
            Connection connection = null;
            try {
                Class.forName("com.mysql.cj.jdbc.Driver");
                connection = DriverManager.getConnection(jdbcURL, jdbcUsername, jdbcPassword);
            }catch (SQLException | ClassNotFoundException e) {
                e.printStackTrace();
            } 
            return connection;
        }

    public Student selectStudent(int id) {
        Student student = null;
        try {
            Connection connection = getConnection();
            PreparedStatement prepStatement = connection.prepareStatement(SELECT_STUDENT_ID);
            prepStatement.setInt(1, id);
            ResultSet rSet = prepStatement.executeQuery();
            while(rSet.next()) {
                String name = rSet.getString("name");
                String email = rSet.getString("email");
                student = new Student(id, name, email);
            }
        } catch (SQLException e) {
            e.printStackTrace();
            }
        return student;
    }

最后，应该显示的jsp表单。

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, intial-scale=1 shink-to-fit=yes">

    <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/css/bootstrap.min.css"
     integrity="sha384..." crossorigin="anonymous">
</head>
<body>
    <nav class="navbar navbar-dark bg-primary pd-8">
         <a class="navbar-brand">&nbsp;&nbsp;&nbsp;&nbsp;XYZ University</a>
    </nav>
    <div class="container col-md-5 p-4">
        <div class="card">
            <div class="card-body">

                <% if (request.getAttribute("student") != null) { %>
               <!-- form display depends on whether there is data in the table -->
                    <form action="<%=request.getContextPath()%>/update" method="post">
                    <% } else { %>
                    <form action="<%=request.getContextPath()%>/insert" method="post">
                    <% } %>
    
                    <div>
                        <h2>
                        <% if (request.getAttribute("student") != null) { %>
                            Edit Student
                        <% } else { %>
                            Add New Student
                        <% } %>
                        </h2>
                    </div>

                <% if (request.getAttribute("student") != null) { %>
                    <input type="hidden" name="id" value="<%=request.getAttribute("student.id") %>" />
                <% } %>

                <fieldset class="form-group">
                <legend>Name</legend>
                <% if (request.getAttribute("student") != null) { %>
                   <input type="text" value="<%=request.getAttribute("student.name") %>" class="form-control" name="name" required="required">
                <% }  else { %>
                    <input type="text" value="" class="form-control" name="name" required="required">
                <% } %>
                </fieldset>

                <fieldset class="form-group">
                <legend>Email</legend>
                <% if (request.getAttribute("student") != null) { %>
                    <input type="text" value="<%=request.getAttribute("student.email") %>" class="form-control" name="email">
                <% }  else { %>
                    <input type="text" value="" class="form-control" name="email">
                <% } %>     
                </fieldset>
                <button type="submit" class="t-3 btn btn-success">Save</button>
                </form>
            </div>
        </div>
    </div>

</body>
</html>

我以为我是通过将编辑url设置为href="<%=request.getContextPath()%>/edit?id=<%=studentDetails.getId()%>“获得id值的，但是表单打开时使用的是一个空值，我不知道我哪里出错了，也不知道如何分配这个值。

真的不知道现在该做什么，我已经尝试寻找解决办法，但似乎没有人能帮助我的问题，任何帮助都会被感激。

java

jsp

servlets

回答 1

Stack Overflow用户

回答已采纳

发布于 2021-08-01 16:40:16

问题是您的request属性的名称是student

request.setAttribute("student", currentStudent);

但是您的属性查找代码正在查找student.id，然后返回null。

<input type="hidden" name="id" value="<%=request.getAttribute("student.id") %>" />

因此，您需要先获取该属性，然后再获取它的属性，以便将表单<input>填充为

<input type="hidden" name="id" value="<%= ((Student) request.getAttribute("student")).getId() %>" />
<input type="text" name="name" value="<%= ((Student) request.getAttribute("student")).getName() %>" ... />
<input type="text" name="email" value="<%= ((Student) request.getAttribute("student")).getEmail() %>" ... />

request.getAttribute()方法的返回类型是Object，因此，在使用getter访问属性之前，需要对Student进行强制转换。这意味着JSP页面也需要一个import指令。

<%@ page import="model.Student" %>

但是，我建议使用JSP表达式语言语法来缩短这些查找

<input type="hidden" name="id" value="${student.id}" />
<input type="text" name="name" value="${student.name}" class="form-control" required="required" />
<input type="text" name="email" value="${student.email}" class="form-control" />

这看起来更干净，更易读，不需要类型转换，并且优雅地处理null值。您甚至不需要所有这些null检查，因为如果value属性是null，则student将自动设置为""。

所以，你所有的form-group

<fieldset class="form-group">
    <legend>First Name</legend>
    <% if (request.getAttribute("student") != null) { %>
        <input type="text" value="${student.firstname}" class="form-control" 
               name="firstname" required="required">
    <% }  else { %>
        <input type="text" value="" class="form-control" name="firstname" required="required">
    <% } %>
</fieldset>

可以简化为几行使用EL。

<fieldset class="form-group">
    <legend>First Name</legend>
    <input type="text" value="${student.firstname}" class="form-control"
           name="fistname" required="required">
</fieldset>

票数 1

页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持

原文链接：

https://stackoverflow.com/questions/68606769

复制

相似问题

问使用servlet使用id打开jsp编辑页
EN

回答 1

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问使用servlet使用id打开jsp编辑页EN

回答 1

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问使用servlet使用id打开jsp编辑页
EN