jsp的前身就是Servlet。Servlet就是在服務(wù)器端運(yùn)行的一段小程序。一個(gè)Servlet就是一個(gè)Java類，并且可以通過(guò)“請(qǐng)求-響應(yīng)”編程模型來(lái)訪問(wèn)的這個(gè)駐留在服務(wù)器內(nèi)存的Servlet程序。
2.Tomcat容器等級(jí)Tomcat的容器分為4個(gè)等級(jí)，Servlet的容器管理Context容器，一個(gè)Context對(duì)應(yīng)一個(gè)Web工程。
編寫一個(gè)Servlet程序大體上需要3個(gè)步驟：繼承HttpServlet-->重寫doGet（）或者doPost（）方法-->在web.xml中注冊(cè)Servlet。
HttpServlet的繼承關(guān)系如圖：
重寫doGet還是doPost方法需要根據(jù)請(qǐng)求方式而定。
一、編寫一個(gè)類繼承自HttPRequest并重寫doGet（或者doPost方法）在項(xiàng)目的src目錄下新建一個(gè)servlet.MyServlet.java
1 package servlet; 2 3 import java.io.IOException; 4 import java.io.PrintWriter; 5 6 import javax.servlet.ServletException; 7 import javax.servlet.http.HttpServlet; 8 import javax.servlet.http.HttpServletRequest; 9 import javax.servlet.http.HttpServletResponse;10 11 /** 繼承自HttpServlet */12 public class HelloServlet extends HttpServlet {13 14 /** 重寫doGet方法 */15 @Override16 protected void doGet(HttpServletRequest request, HttpServletResponse response)17 throws ServletException, IOException {18 System.out.println("處理get請(qǐng)求。。。");19 PrintWriter out = response.getWriter();20 out.println("<b>HelloServlet</b>");21 }22 23 /** 重寫doPost方法 */24 @Override25 protected void doPost(HttpServletRequest request, HttpServletResponse response)26 throws ServletException, IOException {27 System.out.println("處理post請(qǐng)求。。。");28 PrintWriter out = response.getWriter();29 out.println("<b>HelloServlet</b>");30 }31 32 }二、在WEB-INF/web.xml中注冊(cè)剛剛新建的Servlet：
1 <?xml version="1.0" encoding="UTF-8"?> 2 <web-app version="2.5" 3 xmlns="http://java.sun.com/xml/ns/javaee" 4 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 5 xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 6 http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"> 7 <display-name></display-name> 8 <welcome-file-list> 9 <welcome-file>index.jsp</welcome-file>10 </welcome-file-list>11 12 <!-- 注冊(cè)Servlet開(kāi)始 -->13 <servlet>14 <servlet-name>HelloServlet</servlet-name>15 <servlet-class>servlet.HelloServlet</servlet-class>16 </servlet>17 <servlet-mapping>18 <servlet-name>HelloServlet</servlet-name>19 <url-pattern>/servlet/HelloServlet</url-pattern>20 </servlet-mapping>21 <!-- 注冊(cè)Servlet結(jié)束 -->22 23 </web-app>
其中servlet-name表示Servlet的名字，servlet-class要寫完成的類的定義（包名.類名），url-pattern表示Servlet的路徑。
在index.jsp中使用自定義的Servlet處理get和post請(qǐng)求。
1 <%@ page language="java" import="java.util.*" contentType="text/html; charset=utf-8"%> 2 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 3 <html> 4 <head> 5 <title>手工編寫的第一個(gè)Servlet</title> 6 </head> 7 8 <body> 9 <h1>第一個(gè)Servlet小例子</h1><hr>10 <a href="servlet/HelloServlet">get方式請(qǐng)求HelloServlet</a><br /><br />11 <form action="servlet/HelloServlet" method="post">12 <input type="submit" value="post方式請(qǐng)求HelloServlet" /> 13 </form>14 </body>15 </html>
發(fā)布項(xiàng)目，運(yùn)行結(jié)果：
一個(gè)Servlet可以在web.xml中配置多個(gè)映射，這樣就可以在URL中使用不同的名字訪問(wèn)相同的Servlet。如下所示：就可以使用給人以假象——好像使用的是asp或者php或者更多的語(yǔ)言。
1 <!-- 注冊(cè)Servlet開(kāi)始 --> 2 <servlet> 3 <servlet-name>HelloServlet</servlet-name> 4 <servlet-class>servlet.HelloServlet</servlet-class> 5 </servlet> 6 <!-- 一個(gè)Servlet可以配置多個(gè)映射，向下面這樣配置就可以有多種方式訪問(wèn)Servlet了 --> 7 <servlet-mapping> 8 <servlet-name>HelloServlet</servlet-name> 9 <url-pattern>/servlet/HelloServlet</url-pattern>10 </servlet-mapping>11 <servlet-mapping>12 <servlet-name>HelloServlet</servlet-name>13 <url-pattern>/servlet/HelloServlet.asp</url-pattern>14 </servlet-mapping>15 <servlet-mapping>16 <servlet-name>HelloServlet</servlet-name>17 <url-pattern>/servlet/HelloServlet.php</url-pattern>18 </servlet-mapping>19 <servlet-mapping>20 <servlet-name>HelloServlet</servlet-name>21 <!-- *表示任意名稱均可 -->22 <url-pattern>/servlet/hello/*</url-pattern>23 </servlet-mapping>24 <!-- 注冊(cè)Servlet結(jié)束 -->
1.src-->new Servlet。
2.重寫doGet（）或者doPost（）方法。
3.部署運(yùn)行。
通過(guò)MyEclipse創(chuàng)建Servlet的時(shí)候它默認(rèn)繼承自HttpServlet。默認(rèn)勾選覆寫init（）、destory（）、doGet（）和doPost（）方法，并且自動(dòng)向web.xml中注冊(cè)該Servlet。
可以發(fā)現(xiàn)使用MyEclipse創(chuàng)建的Servlet它已經(jīng)自動(dòng)為我們生成了輸出的html模板，我們只需要做很少的改動(dòng)即可。
5.Servlet的執(zhí)行流程和生命周期
用戶點(diǎn)擊超鏈接向Servlet發(fā)送請(qǐng)求-->服務(wù)器在web.xml中的servlet-mapping尋找與該Servlet相對(duì)應(yīng)的URL地址-->找到對(duì)應(yīng)的Servlet名字-->根據(jù)Servlet的名字找到和該Servlet相關(guān)的處理類-->根據(jù)請(qǐng)求的方式不同確定是調(diào)用doGet還是doPost方法。
一個(gè)Servlet的生命周期大致分為3個(gè)階段：
1.客戶端發(fā)送請(qǐng)求給服務(wù)器。
2.服務(wù)器開(kāi)始接受，先判斷該請(qǐng)求的servlet實(shí)例是否存在，如果不存在先裝載一個(gè)servlet類并創(chuàng)建實(shí)例。
如果存在則直接調(diào)用該servlet的service方法，之后進(jìn)行判斷是調(diào)用 doGet方法還是doPost方法。
3.servlet創(chuàng)建實(shí)例后，調(diào)用init方法進(jìn)行初始化。之后調(diào)用servce方法，判斷是調(diào)用doGet方法還是doPost方法。
4.最后判斷服務(wù)器是否關(guān)閉，如果關(guān)閉則調(diào)用destroy方法。
下面這個(gè)例子展示了Servlet的生命周期：
首先是一個(gè)Servlet：TestServlet1
1 package servlet; 2 3 import java.io.IOException; 4 import java.io.PrintWriter; 5 6 import javax.servlet.ServletException; 7 import javax.servlet.http.HttpServlet; 8 import javax.servlet.http.HttpServletRequest; 9 import javax.servlet.http.HttpServletResponse;10 11 public class TestServlet1 extends HttpServlet {12 13 public TestServlet1() {14 System.out.println("TestServlet1構(gòu)造方法被執(zhí)行！");15 }16 17 public void destroy() {18 System.out.println("TestServlet1銷毀方法被執(zhí)行！");19 }20 21 public void doGet(HttpServletRequest request, HttpServletResponse response)22 throws ServletException, IOException {23 24 System.out.println("TestServlet1的doGet方法被執(zhí)行！");25 response.setContentType("text/html;charset=utf-8");26 PrintWriter out = response.getWriter();27 out.println("<!DOCTYPE HTML PUBLIC /"-//W3C//DTD HTML 4.01 Transitional//EN/">");28 out.println("<HTML>");29 out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");30 out.println(" <BODY>");31 out.println("<h1>你好我是TestServlet1</h1>");32 out.println(" </BODY>");33 out.println("</HTML>");34 out.flush();35 out.close();36 }37 38 public void doPost(HttpServletRequest request, HttpServletResponse response)39 throws ServletException, IOException {40 System.out.println("TestServlet1的doPost方法被執(zhí)行！");41 doGet(request, response);// 讓doPost與doGet執(zhí)行相同的操作42 }43 44 public void init() throws ServletException {45 System.out.println("TestServlet1的初始化方法被執(zhí)行！");46 }47 48 }主頁(yè)index.jsp
1 <%@ page language="java" import="java.util.*" contentType="text/html; charset=utf-8"%> 2 <% 3 String path = request.getContextPath(); 4 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; 5 %> 6 7 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 8 <html> 9 <head>10 <base href="<%=basePath%>">11 <title>Servlet的生命周期</title>12 </head>13 14 <body>15 <h1>Servlet的生命周期</h1><hr />16 <a href = "servlet/TestServlet1">以get方式請(qǐng)求TestServlet1</a>17 </body>18 </html>
當(dāng)服務(wù)器啟動(dòng)之后我們第一次訪問(wèn)index.jsp的時(shí)候，構(gòu)造方法，初始化方法和doGet（）方法執(zhí)行
當(dāng)我們?cè)俅握?qǐng)求該頁(yè)面的時(shí)候，只有doGet()方法被執(zhí)行：
服務(wù)器關(guān)閉的時(shí)候銷毀方法執(zhí)行。
6.Tomcat裝載Servlet的3種情況在下列時(shí)刻Servlet容器會(huì)加載Servlet：
1.Servlet容器啟動(dòng)時(shí)自動(dòng)裝載某些Servlet，實(shí)現(xiàn)它只需要在web.xml文件中的<servlet></servlet>之間添加以下代碼：
<load-on-startup>1</load-on-startup>
其中，數(shù)字越小表示優(yōu)先級(jí)越高。
例如：我們?cè)趙eb.xml中設(shè)置TestServlet2的優(yōu)先級(jí)為1，而TestServlet1的優(yōu)先級(jí)為2，啟動(dòng)和關(guān)閉Tomcat：
優(yōu)先級(jí)高的先啟動(dòng)也先關(guān)閉。
2.客戶端首次向某個(gè)Servlet發(fā)送請(qǐng)求。【例子詳見(jiàn)Servlet生命周期的那個(gè)例子】
3.Servlet類被修改后，Tomcat容器會(huì)重新裝載Servlet。
Servlet被裝載后，Servlet容器會(huì)創(chuàng)建一個(gè)Servlet實(shí)例，并且調(diào)用Servlet的init()方法進(jìn)行初始化，在Servlet的真?zhèn)€生命周期內(nèi)init()方法只被調(diào)用一次。
7.Servlet與JSP內(nèi)置對(duì)象的對(duì)應(yīng)關(guān)系
用戶在reg.jsp中填寫注冊(cè)表單，使用post方式將數(shù)據(jù)發(fā)送到一個(gè)名稱為servlet.RegServlet的Servlet處理【Servlet的doPost()方法】，Servlet將用戶信息封裝成一個(gè)Users對(duì)象存儲(chǔ)在session中，講請(qǐng)求轉(zhuǎn)發(fā)到userinfo.jsp。在userinfo.jsp中通過(guò)<jsp:useBean>指令從session中取出保存的用戶對(duì)象，通過(guò)<jsp:getPerproty>指令顯示用戶對(duì)象的各個(gè)字段。
1 package entity; 2 3 import java.util.Date; 4 5 /** 用戶實(shí)體類 */ 6 public class Users { 7 private String username; 8 private String passWord; 9 private String email;10 private String sex;11 private Date birthday;12 private String[] favorites;13 private String introduce; // 自我介紹14 private boolean flag; // 是否接受協(xié)議15 16 public Users() {17 }18 19 public String getUsername() {20 return username;21 }22 23 public void setUsername(String username) {24 this.username = username;25 }26 27 public String getPassword() {28 return password;29 }30 31 public void setPassword(String password) {32 this.password = password;33 }34 35 public String getEmail() {36 return email;37 }38 39 public void setEmail(String email) {40 this.email = email;41 }42 43 public String getSex() {44 return sex;45 }46 47 public void setSex(String sex) {48 this.sex = sex;49 }50 51 public Date getBirthday() {52 return birthday;53 }54 55 public void setBirthday(Date birthday) {56 this.birthday = birthday;57 }58 59 public String[] getFavorites() {60 return favorites;61 }62 63 public void setFavorites(String[] favorites) {64 this.favorites = favorites;65 }66 67 public String getIntroduce() {68 return introduce;69 }70 71 public void setIntroduce(String introduce) {72 this.introduce = introduce;73 }74 75 public boolean isFlag() {76 return flag;77 }78 79 public void setFlag(boolean flag) {80 this.flag = flag;81 }82 83 }用戶實(shí)體entity.Users.java1 <%@ page language="java" import="java.util.*" contentType="text/html;charset=utf-8"%> 2 3 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 4 <html> 5 <head> 6 <title>用戶注冊(cè)</title> 7 <style type="text/CSS"> 8 .label{ 9 width: 20% 10 }11 .controler{12 width: 80% 13 }14 </style> 15 <script type="text/Javascript" src="js/Calendar3.js"></script>16 </head>17 18 <body>19 <h1>用戶注冊(cè)</h1>20 <hr>21 <form name="regForm" action="servlet/RegServlet" method="post" >22 <table border="0" width="800" cellspacing="0" cellpadding="0">23 <tr>24 <td class="lalel">用戶名：</td>25 <td class="controler"><input type="text" name="username" /></td>26 </tr>27 <tr>28 <td class="label">密碼：</td>29 <td class="controler"><input type="password" name="password" ></td>30 31 </tr>32 <tr>33 <td class="label">確認(rèn)密碼：</td>34 <td class="controler"><input type="password" name="confirmpass" ></td>35 36 </tr>37 <tr>38 <td class="label">電子郵箱：</td>39 <td class="controler"><input type="text" name="email" ></td>40 41 </tr>42 <tr>43 <td class="label">性別：</td>44 <td class="controler"><input type="radio" name="sex" checked="checked" value="Male">男<input type="radio" name="sex" value="Female">女</td>45 </tr>46 47 <tr>48 <td class="label">出生日期：</td>49 <td class="controler">50 <input name="birthday" type="text" id="control_date" size="10"51 maxlength="10" onclick="new Calendar().show(this);" readonly="readonly" />52 </td>53 </tr>54 <tr>55 <td class="label">愛(ài)好：</td>56 <td class="controler">57 <input type="checkbox" name="favorite" value="nba"> NBA 58 <input type="checkbox" name="favorite" value="music"> 音樂(lè) 59 <input type="checkbox" name="favorite" value="movie"> 電影 60 <input type="checkbox" name="favorite" value="internet"> 上網(wǎng) 61 </td>62 </tr>63 <tr>64 <td class="label">自我介紹：</td>65 <td class="controler">66 <textarea name="introduce" rows="10" cols="40"></textarea>67 </td>68 </tr>69 <tr>70 <td class="label">接受協(xié)議：</td>71 <td class="controler">72 <input type="checkbox" name="isAccept" value="true">是否接受霸王條款73 </td>74 </tr>75 <tr>76 <td colspan="2" align="center">77 <input type="submit" value="注冊(cè)"/> 78 <input type="reset" value="取消"/> 79 </td>80 </tr>81 </table>82 </form>83 </body>84 </html>注冊(cè)頁(yè)reg.jsp
1 <%@ page language="java" import="java.util.*,java.text.*" contentType="text/html; charset=utf-8"%> 2 <%@ page import="entity.Users" %> 3 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 4 <html> 5 <head> 6 <title>用戶信息顯示</title> 7 <style type="text/css"> 8 .title{ 9 width: 30%; 10 background-color: #CCC;11 font-weight: bold;12 }13 .content{14 width:70%;15 background-color: #CBCFE5;16 }17 18 </style> 19 </head>20 21 <body>22 <h1>用戶信息</h1>23 <hr>24 <center>25 <jsp:useBean id="regUser" class="entity.Users" scope="session"/> 26 <table width="600" cellpadding="0" cellspacing="0" border="1">27 <tr>28 <td class="title">用戶名：</td>29 <td class="content"> <jsp:getProperty name="regUser" property="username"/></td>30 </tr>31 <tr>32 <td class="title">密碼：</td>33 <td class="content"> <jsp:getProperty name="regUser" property="password"/></td>34 </tr>35 <tr>36 <td class="title">性別：</td>37 <td class="content"> <jsp:getProperty name="regUser" property="sex"/></td>38 </tr>39 <tr>40 <td class="title">E-mail：</td>41 <td class="content"> <jsp:getProperty name="regUser" property="email"/></td>42 </tr>43 <tr>44 <td class="title">出生日期：</td>45 <td class="content"> 46 <% 47 SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日");48 String date = sdf.format(regUser.getBirthday());49 %>50 <%=date%>51 </td>52 </tr>53 <tr>54 <td class="title">愛(ài)好：</td>55 <td class="content"> 56 <% 57 String[] favorites = regUser.getFavorites();58 if(favorites!=null){59 for(String f:favorites)60 {61 %>62 <%=f%> 63 <% 64 }65 }66 %>67 </td>68 </tr>69 <tr>70 <td class="title">自我介紹：</td>71 <td class="content"> <jsp:getProperty name="regUser" property="introduce"/></td>72 </tr>73 <tr>74 <td class="title">是否介紹協(xié)議：</td>75 <td class="content"> <jsp:getProperty name="regUser" property="flag"/></td>76 </tr>77 </table>78 </center>79 </body>80 </html>用戶信息顯示頁(yè)userinfo.jsp 1 package servlet; 2 3 import java.io.IOException; 4 import java.text.ParseException; 5 import java.text.SimpleDateFormat; 6 import java.util.Date; 7 8 import javax.servlet.ServletException; 9 import javax.servlet.http.HttpServlet;10 import javax.servlet.http.HttpServletRequest;11 import javax.servlet.http.HttpServletResponse;12 13 import entity.Users;14 15 public class RegServlet extends HttpServlet {16 17 public RegServlet() {18 super();19 }20 21 public void destroy() {22 super.destroy(); // Just puts "destroy" string in log23 }24 25 public void doGet(HttpServletRequest request, HttpServletResponse response)26 throws ServletException, IOException {27 28 doPost(request, response);//因?yàn)楸韱问莗ost方式提交的29 }30 31 public void doPost(HttpServletRequest request, HttpServletResponse response)32 throws ServletException, IOException {33 34 request.setCharacterEncoding("utf-8");35 36 Users u = new Users();37 String username,password,email,introduce,sex,isAccept;38 Date birthday;39 String[]favorites;40 41 SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");42 43 try {44 45 username = request.getParameter("username");46 password = request.getParameter("password");47 sex = request.getParameter("sex");48 email = request.getParameter("email");49 introduce = request.getParameter("introduce");50 51 if (request.getParameter("birthday")!=null&&request.getParameter("birthday").length()!=0) {52 birthday = sdf.parse(request.getParameter("birthday"));53 }else {54 birthday = new Date();55 }56 57 favorites = request.getParameterValues("favorite");//getParamterValues返回字符串?dāng)?shù)組58 isAccept = request.getParameter("isAccept");59 60 u.setUsername(username);61 u.setPassword(password);62 u.setEmail(email);63 u.setBirthday(new Date());64 u.setIntroduce(introduce);65 u.setFavorites(favorites);66 u.setSex(sex);67 u.setFlag(isAccept!=null&&isAccept.equals("true")?true:false);68 69 //把注冊(cè)成功的用戶對(duì)象保存在session中70 request.getSession().setAttribute("regUser", u);71 72 request.getRequestDispatcher("../userinfo.jsp").forward(request, response);73 } catch (ParseException e) {74 e.printStackTrace();75 }76 }77 78 public void init() throws ServletException {79 }80 81 }處理用戶注冊(cè)的Servlet：RegServlet
相對(duì)路徑就是相對(duì)于當(dāng)前頁(yè)面的路徑，絕對(duì)路徑就是相對(duì)于項(xiàng)目根目錄的路徑（絕對(duì)路徑需要使用到path變量）。
1 <%@ page language="java" import="java.util.*" contentType="text/html; charset=utf-8"%> 2 <% 3 String path = request.getContextPath(); 4 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; 5 %> 6 7 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 8 <html> 9 <head>10 <base href="<%=basePath%>">11 <title>Servlet路徑跳轉(zhuǎn)</title>12 </head>13 14 <body>15 <h1>Servlet路徑跳轉(zhuǎn)</h1>16 <!-- 使用相對(duì)路徑訪問(wèn)HelloServlet -->17 <a href="servlet/HelloServlet">使用相對(duì)路徑訪問(wèn)servlet</a><br />18 19 <!-- 使用絕對(duì)路徑訪問(wèn)HelloServlet，使用path變量 -->20 項(xiàng)目的根目錄：<%=path %><br />21 <a href="<%=path %>/servlet/HelloServlet">使用相對(duì)路徑訪問(wèn)servlet</a><br />22 </body>23 </html>
在web.xml中注冊(cè)的Servlet的路徑寫法是絕對(duì)路徑：
1 <?xml version="1.0" encoding="UTF-8"?> 2 <web-app version="2.5" 3 xmlns="http://java.sun.com/xml/ns/javaee" 4 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 5 xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 6 http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"> 7 <display-name></display-name> 8 9 <!-- Servlet注冊(cè)開(kāi)始 -->10 <servlet>11 <description>This is the description of my J2EE component</description>12 <display-name>This is the display name of my J2EE component</display-name>13 <servlet-name>HelloServlet</servlet-name>14 <servlet-class>servlet.HelloServlet</servlet-class>15 </servlet>16 <servlet-mapping>17 <servlet-name>HelloServlet</servlet-name>18 <url-pattern>/servlet/HelloServlet</url-pattern><!-- Servlet的路徑是絕對(duì)路徑 -->19 </servlet-mapping>20 <!-- Servlet注冊(cè)結(jié)束 -->21 22 <welcome-file-list>23 <welcome-file>index.jsp</welcome-file>24 </welcome-file-list>25 </web-app>在Servlet之中路徑的跳轉(zhuǎn)問(wèn)題：
index.jsp中有一個(gè)鏈接指向servlet.TestServlet
<a href="servlet/TestServlet">訪問(wèn)TestServlet，跳轉(zhuǎn)到Test.jsp</a>
servlet.TestServlet的doPost()和doGet()方法如下：
1 public void doGet(HttpServletRequest request, HttpServletResponse response) 2 throws ServletException, IOException { 3 4 doPost(request, response); 5 } 6 7 public void doPost(HttpServletRequest request, HttpServletResponse response) 8 throws ServletException, IOException { 9 // 1.使用請(qǐng)求重定向的方式跳轉(zhuǎn)到test.jsp10 // response.sendRedirect("../test.jsp");11 // 也可以使用絕對(duì)路徑的方式request.getContextPath12 // response.sendRedirect(request.getContextPath()+"/test.jsp");13 14 // 2.使用服務(wù)器內(nèi)部跳轉(zhuǎn)的方式15 // request.getRequestDispatcher("../test.jsp").forward(request, response);16 request.getRequestDispatcher("/test.jsp").forward(request, response);17 }在TestServlet中完成到網(wǎng)站根目錄下的跳轉(zhuǎn)有兩種方式重定向和服務(wù)器內(nèi)部轉(zhuǎn)發(fā)，其中URL的寫法也有2種方式：絕對(duì)路徑和相對(duì)路徑。相對(duì)路徑使用..即可，而絕對(duì)路徑重定向需要依賴request.getContextPath()方法取得上下文環(huán)境，而服務(wù)器內(nèi)部轉(zhuǎn)發(fā)中的斜線就表示項(xiàng)目的根目錄。
開(kāi)發(fā)中一般在web.xml中配置Servlet的路徑為表單所在路徑，這樣在表單中只需要書寫Servlet名字即可。在開(kāi)發(fā)中應(yīng)該盡量避免../的寫法。
10.階段案例——使用Servlet完成用戶登錄用戶名和密碼都是admin，登陸成功則使用服務(wù)器內(nèi)部轉(zhuǎn)發(fā)到login_success.jsp，顯示登錄成功的用戶名。登錄失敗則重定向到login_failure.jsp。
把login.jsp中表單的action屬性改為需要處理登錄的Servlet
1 <form action="servlet/LoginServlet" method="post" name="loginForm">2 <!-- 代碼省略 -->3 </form>
1 package org.po; 2 3 /** 4 * 用戶類-javabean 5 */ 6 public class Users { 7 private String username; 8 private String password; 9 10 public Users() {11 }12 13 public String getUsername() {14 return username;15 }16 17 public void setUsername(String username) {18 this.username = username;19 }20 21 public String getPassword() {22 return password;23 }24 25 public void setPassword(String password) {26 this.password = password;27 }28 29 }用戶實(shí)體類org.po.Users 1 public void doGet(HttpServletRequest request, HttpServletResponse response) 2 throws ServletException, IOException { 3 4 doPost(request, response); 5 } 6 7 public void doPost(HttpServletRequest request, HttpServletResponse response) 8 throws ServletException, IOException { 9 10 Users u = new Users();11 String username = request.getParameter("username");12 String password = request.getParameter("password");13 u.setUsername(username);14 u.setPassword(password);15 16 if (u.getUsername().equals("admin")&&u.getPassword().equals("admin")) {17 request.getSession().setAttribute("username", username);18 request.getRequestDispatcher("/login_success.jsp").forward(request, response);19 }else {20 response.sendRedirect("../login_failure.jsp");21 }22 }處理用戶登錄的LoginServletServlet高級(jí) 1.獲取初始化參數(shù)在web.xml中配置Servlet時(shí)，可以配置一些初始化參數(shù)。而在Servlet中可以通過(guò)ServletConfig接口提供的方法來(lái)取得這些參數(shù)。
1.首先在index.jsp中建立一條超鏈接指向servlet.GetInitParameterServlet。
<a href = "servlet/GetInitParameterServlet">獲取Servlet的初始化參數(shù)</a>
2.在web.xml中配置該Servlet的初始化參數(shù)：
1 <?xml version="1.0" encoding="UTF-8"?> 2 <web-app version="2.5" 3 xmlns="http://java.sun.com/xml/ns/javaee" 4 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 5 xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 6 http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"> 7 <display-name></display-name> 8 9 <!-- 注冊(cè)Servlet開(kāi)始 -->10 <servlet>11 <description>This is the description of my J2EE component</description>12 <display-name>This is the display name of my J2EE component</display-name>13 <servlet-name>GetInitParameterServlet</servlet-name>14 <servlet-class>servlet.GetInitParameterServlet</servlet-class>15 16 <!-- 配置用戶名初始化參數(shù) -->17 <init-param>18 <param-name>username</param-name>19 <param-value>admin</param-value>20 </init-param>21 <!-- 配置密碼初始化參數(shù) -->22 <init-param>23 <param-name>password</param-name>24 <param-value>123456</param-value>25 </init-param>26 27 </servlet>28 <!-- 注冊(cè)Servlet結(jié)束 -->29 30 <servlet-mapping>31 <servlet-name>GetInitParameterServlet</servlet-name>32 <url-pattern>/servlet/GetInitParameterServlet</url-pattern>33 </servlet-mapping> 34 <welcome-file-list>35 <welcome-file>index.jsp</welcome-file>36 </welcome-file-list>37 </web-app>web.xml
3.在GetInitParameterServlet的init方法中使用this.getgetInitParameter(String name)方法獲得初始化參數(shù)：
1 package servlet; 2 3 import java.io.IOException; 4 import java.io.PrintWriter; 5 6 import javax.servlet.ServletException; 7 import javax.servlet.http.HttpServlet; 8 import javax.servlet.http.HttpServletRequest; 9 import javax.servlet.http.HttpServletResponse;10 11 public class GetInitParameterServlet extends HttpServlet {12 /* 封裝屬性 */13 private String username ;14 private String password ;15 16 public String getUsername() {17 return username;18 }19 20 public void setUsername(String username) {21 this.username = username;22 }23 24 public String getPassword() {25 return password;26 }27 28 public void setPassword(String password) {29 this.password = password;30 }31 32 public GetInitParameterServlet() {33 super();34 }35 36 public void destroy() {37 super.destroy(); // Just puts "destroy" string in log38 }39 40 public void doGet(HttpServletRequest request, HttpServletResponse response)41 throws ServletException, IOException {42 43 doPost(request, response);44
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