Question

我打算致电getParameter。一切都很好，但当我点击编辑链接时，它会给出NullPointerException。为什么它没有得到价值？

JSP代码：

  <%@page import="teacher.TeacherBAL"%>
  <%@page import="teacher.TeacherBean" %>
  <%@page import="java.util.*" %>
  <%@ page language="java" contentType="text/html; charset=ISO-8859-1"
     pageEncoding="ISO-8859-1"%>
  <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"  "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
    <title>Display Data</title>
</head>
<body>
    <table border=1>
        <th>Name</th>
        <th>Degree</th>
        <th>Delete</th>
        <th>Edit</th>
            <%
                ArrayList teachers = (ArrayList) request.getAttribute("allRecord");
                if (teachers != null) {
                    int a = 0;
                    for (; a < teachers.size(); a++) {
                        TeacherBean teacherBea = (TeacherBean) teachers.get(a);
            %>  
        <tr>
            <td><%=teacherBea.getName()%></td>
            <td><%=teacherBea.getDegree()%></td>
            <td>
                <a href="FetchData?delete=<%=a%>">Delete</a>        
            </td>
            <td>
                <a href="FetchData?click=<%=a%>">Edit</a>   
            </td>
        </tr>
        <%}
            }
        %>
       </table>
    <a href="index.jsp" ><img src="images/back.jpg" height="60"></a>
</body>

Servlet代码：

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {   
    response.setContentType("text/html;charset=UTF-8");
    String edit= request.getParameter("click");
    String del = request.getParameter("delete");
    String req= request.getParameter("show");
    if(del!=null){
        int dele = Integer.parseInt(del);
        TeacherBAL.getTeacher().remove(dele);
        request.setAttribute("allRecord", TeacherBAL.getTeacher());
        RequestDispatcher rd= request.getRequestDispatcher("display.jsp");
        rd.forward(request, response);
    }
    else if(req.equals("ok")){
        request.setAttribute("allRecord", TeacherBAL.getTeacher());
        RequestDispatcher rd= request.getRequestDispatcher("display.jsp");
        rd.forward(request, response);
    }
    else if(edit!=null){
        int num = Integer.parseInt(edit);
        PrintWriter out = response.getWriter();
        out.print(num);
    }
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    String name= request.getParameter("names");
    String degre= request.getParameter("degre");
    if(name!=null && degre!=null){
        TeacherBAL.setTeacher(new TeacherBean(name,degre));
        RequestDispatcher rd= request.getRequestDispatcher("index.jsp");
        rd.forward(request, response);
    }
}

Answer 1

您收到空指针异常，因为单击编辑按钮时未传递delete和show的值。因此，del和req为空，您在req.equals("ok")上收到例外。

servlet中的getParameter

1 个答案: