JavaWeb常见错误

1.<a href="customerServlet?method=add">Add</a>  这里method=add不能有空格,否则报错(空指针异常)

 1 <%@ page language="java" contentType="text/html; charset=ISO-8859-1"

 2     pageEncoding="ISO-8859-1"%>

 3 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

 4 <html>

 5 <head>

 6 <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">

 7 <title>Insert title here</title>

 8 </head>

 9 <body>

10     <a href="customerServlet?method=add">Add</a>

11     <br>

12     <br>

13 

14     <a href="customerServlet?method=query">Query</a>

15     <br>

16     <br>

17 

18     <a href="customerServlet?method=delete">Delete</a>

19     <br>

20     <br>

21 

22 </body>

23 </html>
View Code
 1 package com.ouyang.dao;

 2 

 3 import java.io.IOException;

 4 

 5 import javax.servlet.ServletException;

 6 import javax.servlet.annotation.WebServlet;

 7 import javax.servlet.http.HttpServlet;

 8 import javax.servlet.http.HttpServletRequest;

 9 import javax.servlet.http.HttpServletResponse;

10 

11 @WebServlet("/customerServlet")

12 public class CustomerServlet extends HttpServlet {

13     private static final long serialVersionUID = 1L;

14 

15     protected void doGet(HttpServletRequest request,

16             HttpServletResponse response) throws ServletException, IOException {

17         doPost(request, response);

18     }

19 

20     protected void doPost(HttpServletRequest request,

21             HttpServletResponse response) throws ServletException, IOException {

22         String method = request.getParameter("method");

23 

24         switch (method) {

25         case "add":

26             add(request, response);

27             break;

28         case "query":

29             query(request, response);

30             break;

31         case "delete":

32             delete(request, response);

33             break;

34 

35         }

36 

37     }

38 

39     private void delete(HttpServletRequest request, HttpServletResponse response)

40             throws ServletException, IOException {

41         System.out.println("delete");

42     }

43 

44     private void query(HttpServletRequest request, HttpServletResponse response)

45             throws ServletException, IOException {

46         System.out.println("query");

47     }

48 

49     private void add(HttpServletRequest request, HttpServletResponse response)

50             throws ServletException, IOException {

51         System.out.println("add");

52 

53     }

54 

55 }
View Code

 2.url-pattern 中在建立Servlet时前面不应该加"/".否则会报错

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