运行方法取决于 JSP link 在 Servlet 上使用 switch 语句

Question

您好，我对使用 JSP 和 servlet 构建网页还很陌生，我正在尝试根据用户点击的 link/button 将 switch 语句用于运行函数但是我尝试过的每个代码都无法运行函数或重定向到新页面，任何帮助将不胜感激我尝试使用 html 标签和 request.getContextPath 但无济于事......它 returns 404 错误或 returns 空白页

这是我的 servlet 代码

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();
                } 
            default:
                try {
                    listAllStudents(request, response);
                } catch (ServletException | IOException | SQLException e) {
                    e.printStackTrace();
                } 
                break; 
            } 
    }

    // functions to fetch data from studentDao and display data on appropriate jsp
    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"); //home page week04/StudentServlet | list all objects from table
        dispatch.forward(request, response);
    }
    
    private void showNewForm(HttpServletRequest request, HttpServletResponse response) 
        throws ServletException, IOException {
        RequestDispatcher dispatch = request.getRequestDispatcher("student-form.jsp");
        dispatch.forward(request, response);
    }

    private void insertStudent(HttpServletRequest request, HttpServletResponse response) 
            throws SQLException, IOException{
        String name = request.getParameter("name");
        String email = request.getParameter("email");
        Student newStudent = new Student(name, email);
        studentDao.insertStudent(newStudent); //student object inserted to table 
        response.sendRedirect("listStudents"); //redirect to home page
    }
    
    private void deleteStudent(HttpServletRequest request, HttpServletResponse response) 
            throws SQLException, IOException {
        int id = Integer.parseInt(request.getParameter("id"));
        studentDao.deleteStudent(id); //student object deleted
        response.sendRedirect("listStudents");
    }
    
    private void updateStudent(HttpServletRequest request, HttpServletResponse response) 
            throws SQLException, IOException{
        int id = Integer.parseInt(request.getParameter("id"));
        String name = request.getParameter("name");
        String email = request.getParameter("email");
        Student updateStudent = new Student(id, name, email);
        studentDao.updateStudent(updateStudent); //student object updated
        response.sendRedirect("listStudents");
    }
    
    private void editStudent(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException {
        int id = Integer.parseInt(request.getParameter("id"));
        Student currentStudent = studentDao.selectStudent(id);
        RequestDispatcher dispatch = request.getRequestDispatcher("student-form.jsp");
        request.setAttribute("student", currentStudent); //student object updated
        dispatch.forward(request, response);
    }

}

这是我的 jsp 页面

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1" import="java.util.*" import="week04.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>
    <div class="container-fluid">
    <nav class="navbar navbar-dark bg-primary pd-8">
        <a class="navbar-brand">XYZ University</a>
    </nav>
    <div class="container">

            <div class="container-fluid p-4">
               <a href="/new" class="btn btn-success" action="/new">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>
                    <%
                     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()%>/update">Update</a>
                                &nbsp;&nbsp;&nbsp;&nbsp; <a href="<%=request.getContextPath()%>/delete">Delete</a></td>
                        </tr>
                    <% 
                            }
                     }
                    %>
                </tbody>
                
            </table>
            </div>
        </div>
         
    </body>
</html>

这是我的 xml 文件

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:web="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd http://java.sun.com/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee" id="WebApp_ID" version="2.4">
  
  <servlet>
    <description></description>
    <display-name>StudentServlet</display-name>
    <servlet-name>StudentServlet</servlet-name>
    <servlet-class>week04.web.StudentServlet</servlet-class>
  </servlet>
  
  <servlet-mapping>
    <servlet-name>StudentServlet</servlet-name>
    <url-pattern>/StudentServlet</url-pattern>
  </servlet-mapping>
</web-app>

任何对我做错的帮助将不胜感激。

Answer 1

您需要告诉 web.xml 中的 servlet 它处理指定的 URL。

  <servlet-mapping>
    <servlet-name>StudentServlet</servlet-name>
    <url-pattern>/StudentServlet</url-pattern>
    <url-pattern>/new</url-pattern>
  </servlet-mapping>

此外，必须正确指定 href。

<div class="container-fluid p-4">
    <a href="new" class="btn btn-success" action="/new">Add Student</a>
</div>

运行方法取决于 JSP link 在 Servlet 上使用 switch 语句

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运行 方法取决于 JSP link 在 Servlet 上使用 switch 语句

Running methods depending JSP link using switch statements on Servlets

web.xml

servlets

http-status-code-404

path-parameter

运行方法取决于 JSP link 在 Servlet 上使用 switch 语句