使用Servlet上的switch语句运行取决于JSP链接的方法[重复]

Posted 2023-03-25

【中文标题】使用Servlet上的switch语句运行取决于JSP链接的方法[重复]

【英文标题】：Running methods depending JSP link using switch statements on Servlets [duplicate]

【发布时间】：2021-10-05 02:30:29

【问题描述】：

您好，我对使用 JSP 和 servlet 构建网页还很陌生，我正在尝试使用 switch 语句来根据用户单击的链接/按钮运行函数，但是我尝试过的每个代码都无法运行该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 标记和 request.getContextPath 但无济于事......它返回 404 错误或返回空白页

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>

对我做错的任何帮助将不胜感激。

【参考方案1】：

您需要在 web.xml 中告诉 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>

另外，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>

【讨论】：

谢谢@Stanislav Omelianenko 解决了我的问题不知道谁将我的问题标记为重复但其他来源没有帮助