Servlet

  1. servlet简介
    • servlet+applet :服务器端小程序，
    • 一个特殊的Java类
    • 通过“请求-响应”来访问这个程序
    • 与HTTP紧密联系，通过servler几乎可以处理HTTP所有问题
  2. Tomcat容器等级
    Tomcat容器分为四个等级
    Container
    　　Engine
    　　     Host
                     Servlet

    一个Context对于一个web工程
  3. 实现一个Servlet
    1. 继承HttpServlet类
    2. 重写doGet()或doPost()   取决于用户提交请求的方式
    3. 在web.xml中注册Servlet
      1        <servlet>
2         <servlet-name>ServletName</servlet-name>
3         <servlet-class>Servlet完全限定名</servlet-class>
4     </servlet>
5     <servlet-mapping>
6         <servlet-name>ServletName</servlet-name>
7         <url-pattern>/.../...</url-pattern>
8     </servlet-mapping>
      View Code
  4. Servlet处理流程
  5. Servlet生命周期
    1. 初始化，init()，整个生命周期中，init()方法只会执行一次
    2. 响应客户端请求，调用service(),由service（）根据请求方式选择执行doGet()还是doPost()
    3. 终止阶段，调用destory()
  6. Tomcat装载Servlet的三种情况
    1. web.xml的<servlet>中加入<load-on-startup>1</load-on-startup>标签，数值越小 优先级越高
    2. 客户端首次请求Servlet
      Servlet的构造函数——>init()——>service()——>doGet()或doPost()，关闭服务器才会执行destory()
    3. Servlet类被修改以后，重新装载Servlet
  7. Servlet与JSP九大内置对象对应关系
  8. 一个注册页面，Servlet获取表单信息

    1. 注册页面register.jsp
       1 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
 2 <%
 3     String path = request.getContextPath();
 4     String basePath = request.getScheme() + "://"
 5             + request.getServerName() + ":" + request.getServerPort()
 6             + path + "/";
 7 %>
 8 
 9 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
10 <html>
11 <head>
12 <base href="<%=basePath%>">
13 
14 <title>My JSP 'index.jsp' starting page</title>
15 <meta http-equiv="pragma" content="no-cache">
16 <meta http-equiv="cache-control" content="no-cache">
17 <meta http-equiv="expires" content="0">
18 <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
19 <meta http-equiv="description" content="This is my page">
20 <!--
21     <link rel="stylesheet" type="text/css" href="styles.css">
22     -->
23 <style type="text/css">
24 .label {
25     width: 20%
26 }
27 
28 .controler {
29     width: 80%
30 }
31 </style>
32 <script type="text/javascript" src="js/Calendar3.js"></script>
33 </head>
34 
35 <body>
36     <form name="regform" action="servlet/LoginServlet" method="post">
37         <table border="1" width="800">
38             <tr>
39                 <td class="lable">用户名</td>
40                 <td class="controler"><input type="text" name="username"></td>
41             </tr>
42 
43             <tr>
44                 <td class="lable">密码</td>
45                 <td class="controler"><input type="password" name="mypassword"></td>
46             </tr>
47 
48             <tr>
49                 <td class="lable">确认密码</td>
50                 <td class="controler"><input type="password"name="confirmpassward"></td>
51             </tr>
52             
53             <tr>
54                 <td class="lable">性别</td>
55                 <td class="controler">
56                     <input type="radio" name="gender"value="Male" checked="checked">男 
57                     <input type="radio"name="gender" value="Female">女
58                 </td>
59             </tr>
60             
61             <tr>
62                 <td class="label">出生日期：</td>
63                 <td class="controler"><input name="birthday" type="text"
64                     id="control_date" size="10" maxlength="10"
65                     onclick="new Calendar().show(this);" readonly="readonly" /></td>
66             </tr>
67 
68             <tr>
69                 <td class="lable">电子邮箱</td>
70                 <td class="controler"><input type="text" name="email"></td>
71             </tr>
72 
73             <tr>
74                 <td class="lable">爱好</td>
75                 <td class="controler">
76                     <input type="checkbox" name="favorite"value="nba">NBA 
77                     <input type="checkbox" name="favorite"value="music">音乐 
78                     <input type="checkbox" name="favorite"value="movie">电影
79                 </td>
80             </tr>
81             
82         </table>
83         <input type="submit" value="注册" />&nbsp;&nbsp; <input type="reset"
84             value="取消">
85     </form>
86 
87 </body>
88 </html>
      View Code

      action指定提交给哪个Servlet处理
    2. 用户信息类UserInfo和LoginServlet
      UserInfo类中封装用户的属性，并生成set get方法
      1 private String username;//用户名
2     private String password;//密码
3     private String gender;//性别
4     private Date birthdar;//出生日期
5     private String email;//邮箱
6     private String[] favorates;//爱好
      UserInfo类
        1 package servlet;
  2 
  3 import java.io.IOException;
  4 import java.text.ParseException;
  5 import java.text.SimpleDateFormat;
  6 
  7 import javax.servlet.ServletException;
  8 import javax.servlet.http.HttpServlet;
  9 import javax.servlet.http.HttpServletRequest;
 10 import javax.servlet.http.HttpServletResponse;
 11 
 12 import entity.UserInfo;
 13 
 14 public class LoginServlet extends HttpServlet {
 15 
 16     /**
 17      * 
 18      */
 19     private static final long serialVersionUID = 1L;
 20 
 21     /**
 22      * Constructor of the object.
 23      */
 24     public LoginServlet() {
 25         super();
 26     }
 27 
 28     /**
 29      * Destruction of the servlet. <br>
 30      */
 31     public void destroy() {
 32         super.destroy(); // Just puts "destroy" string in log
 33         // Put your code here
 34     }
 35 
 36     /**
 37      * The doGet method of the servlet. <br>
 38      * 
 39      * This method is called when a form has its tag value method equals to get.
 40      * 
 41      * @param request
 42      *            the request send by the client to the server
 43      * @param response
 44      *            the response send by the server to the client
 45      * @throws ServletException
 46      *             if an error occurred
 47      * @throws IOException
 48      *             if an error occurred
 49      */
 50     public void doGet(HttpServletRequest request, HttpServletResponse response)
 51             throws ServletException, IOException {
 52 
 53         doPost(request, response);
 54     }
 55 
 56     /**
 57      * The doPost method of the servlet. <br>
 58      * 
 59      * This method is called when a form has its tag value method equals to
 60      * post.
 61      * 
 62      * @param request
 63      *            the request send by the client to the server
 64      * @param response
 65      *            the response send by the server to the client
 66      * @throws ServletException
 67      *             if an error occurred
 68      * @throws IOException
 69      *             if an error occurred
 70      */
 71     public void doPost(HttpServletRequest request, HttpServletResponse response)
 72             throws ServletException, IOException {
 73         UserInfo user = new UserInfo();
 74         
 75         SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
 76         user.setUsername(request.getParameter("username"));
 77         user.setPassword(request.getParameter("mypassword"));
 78         try {
 79             user.setBirthdar(sdf.parse(request.getParameter("birthday")));
 80         } catch (ParseException e) {
 81             e.printStackTrace();
 82         }
 83         user.setGender(request.getParameter("gender"));
 84         user.setEmail(request.getParameter("email"));
 85         
 86         //获取多个复选按钮的值getParameterValues（）
 87         user.setFavorates(request.getParameterValues("favorite"));
 88         
 89         ///把注册成功的用户对象保存在session中session名为userinfo
 90         request.getSession().setAttribute("userinfo", user);
 91         
 92         //跳转到注册成功页面
 93         request.getRequestDispatcher("../success.jsp").forward(request,
 94                 response);
 95 
 96     }
 97 
 98     /**
 99      * Initialization of the servlet. <br>
100      * 
101      * @throws ServletException
102      *             if an error occurs
103      */
104     public void init() throws ServletException {
105         // Put your code here
106         System.out.println("init执行了");
107     }
108 
109 }
      LoginServlet类
      <servlet>
        <servlet-name>LoginServlet</servlet-name>
        <display-name>This is the display name of my J2EE component</display-name>
        <description>This is the description of my J2EE component</description>
        <servlet-class>servlet.LoginServlet</servlet-class>
    </servlet>


    <servlet-mapping>
        <servlet-name>LoginServlet</servlet-name>
        <url-pattern>/servlet/LoginServlet</url-pattern>
    </servlet-mapping>
      web.xml中配置LoginServlet
    3. 注册成功页面
       1 <%@page import="java.text.SimpleDateFormat"%>
 2 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
 3 <%
 4     String path = request.getContextPath();
 5     String basePath = request.getScheme() + "://"
 6             + request.getServerName() + ":" + request.getServerPort()
 7             + path + "/";
 8 %>
 9 
10 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
11 <html>
12 <head>
13 <base href="<%=basePath%>">
14 
15 <title>My JSP 'success.jsp' starting page</title>
16 
17 <meta http-equiv="pragma" content="no-cache">
18 <meta http-equiv="cache-control" content="no-cache">
19 <meta http-equiv="expires" content="0">
20 <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
21 <meta http-equiv="description" content="This is my page">
22 <!--
23     <link rel="stylesheet" type="text/css" href="styles.css">
24     -->
25 
26 </head>
27 
28 <body>
29     <h1>用户信息</h1>
30     <hr>
31     <center>
32         <jsp:useBean id="userinfo" class="entity.UserInfo" scope="session" />
33         <table width="600" cellpadding="0" cellspacing="0" border="1">
34             <tr>
35                 <td class="title">用户名：</td>
36                 <td class="content">&nbsp;
37                     <jsp:getProperty name="userinfo"property="username" />
38                 </td>
39             </tr>
40 
41             <tr>
42                 <td class="title">密码：</td>
43                 <td class="content">&nbsp;
44                     <jsp:getProperty name="userinfo"property="password" />
45                 </td>
46             </tr>
47             
48             <tr>
49                 <td class="title">性别：</td>
50                 <td class="content">&nbsp;
51                     <jsp:getProperty name="userinfo"property="gender" />
52                 </td>
53             </tr>
54             
55             <tr>
56                 <td class="title">出生日期：</td>
57                 <td class="content">&nbsp; 
58                 
59      <%SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日");
60      String date = sdf.format(userinfo.getBirthdar()); %> 
61      <%=date%>
62                 </td>
63             </tr>
64             
65             <tr>
66                 <td class="title">E-mail：</td>
67                 <td class="content">&nbsp;
68                     <jsp:getProperty name="userinfo"property="email" />
69                 </td>
70             </tr>
71 
72             <tr>
73                 <td class="title">爱好：</td>
74                 <td class="content">&nbsp; 
75                 <%
76      String[] favorites = userinfo.getFavorates();
77      for (String f : favorites) {
78  %> 
79  <%=f%> &nbsp;&nbsp; 
80  <%
81      }
82  %>
83                 </td>
84             </tr>
85             
86         </table>
87     </center>
88 </body>
89 </html>
      success.jsp
  9. Servlet路径跳转问题
    绝对路径：放之四海而皆准的路径
    相对路径：相对于当前资源的路径
      “../”来表示上一级目录
     “../../”表示上上级的目录，以此类推。
    下级目录用“/..”表示
    "./"代表目前所在的目录
    以"/"开头：代表根目录。在web.xml的<url-pattern>/servlet/LoginServlet</url-pattern>必须以/开头，这里的/表示项目的更目录
    根目录：最上一级目录，如双击D盘 就进入了D盘的根目录

    内部跳转（请求转发） 和外部跳转（请求重定向）
    • 内部跳转：服务器收到客户端请求后，将请求转发到另一个页面或servlet，这个时候跳转到的目标页面或者servlet可以获取到请求对象,也可以获取到请求中的属性和参数；浏览器的url地址栏不会改变；无法跳转到工程以外的jsp或servlet
      实现方式： 1 request.getRequestDispatcher("XXX.jsp或者servlet").forward(request, response),  

    • 外部跳转：第一次请求后，服务器端向客户端发送了一个指令，让客户端再次请求了一次服务器端，这个时候服务器第二次拿到的request对象已经不是第一次请求的request对象了,所以无法获取到第一次请求里的参数和属性；浏览器url地址栏会发生变化；可以跳转到工程以外的页面或servlet
      实现方式： 1 response.sendRedirect("XXX.jsp或者servlet") 

  1. http请求的get方式和post方式区别

     

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原文地址：https://www.cnblogs.com/gucl/p/8109178.html