前面兩節已經學習了什么是Servlet,Servlet接口函數是哪些、怎么運行、Servlet生命周期是什么? 以及Servlet中的模式匹配URL，web.xml配置和HttpServlet。怎么在Eclipse中新建一個Servlet工程項目。 今天這里主要是創建一個Servlet+JSP的例子。
一、學習之前補充一下web.xml中配置問題
web.xml中<welcome-file-list>配置（（web歡迎頁、首頁））
用於當用戶在url中輸入工程名稱或者輸入web容器url（如http://localhost:8080/）時直接跳轉的頁面.
welcome-file-list的工作原理是，按照welcome-file的.list一個一個去檢查是否web目錄下面存在這個文件，如果存在，繼續下面的工作（或者跳轉到index.html頁面，或者配置有struts的，會直接struts的過濾工作）.如上例，先去webcontent(這里是Eclipse的工程目錄根目錄)下是否真的存在index.html這個文件，如果不存在去找是否存在index.jsp這個文件，以此類推。
還要說的是welcome-file不一定是html或者jsp等文件，也可以是直接訪問一個action。就像我上面配置的一樣，但要注意的是，一定要在webcontent下面建立一個index.action的空文件，然后使用struts配置去跳轉，不然web找不到index.action這個文件，會報404錯誤，
如果配置了servlet的url-pattern是/*，那么訪問localhost:8080/會匹配到該servlet上，而不是匹配welcome-file-list；如果url-pattern是/（該servlet即為默認servlet），如果其他匹配模式都沒有匹配到，則會匹配welcome-file-list。
例如：
FirstServlet.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.annotation.WebServlet; 8 import javax.servlet.http.HttpServlet; 9 import javax.servlet.http.HttpServletRequest; 10 import javax.servlet.http.HttpServletResponse; 11 //@WebServlet("/Firstservlet") 12 public class FirstServlet extends HttpServlet { 13 14 /* (non-Javadoc) 15 * @see javax.servlet.http.HttpServlet#doGet(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse) 16 */ 17 @Override 18 protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 19 System.out.println("處理get()的請求。。。"); 20 PrintWriter pw = resp.getWriter(); 21 pw.write("hello!"); 22 } 23 24 /* (non-Javadoc) 25 * @see javax.servlet.http.HttpServlet#doPost(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse) 26 */ 27 @Override 28 protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 29 30 } 31 }
web.xml 配置
1 <?xml version="1.0" encoding="UTF-8"?> 2 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0"> 3 <display-name>ServletTest</display-name> 4 <welcome-file-list> 5 <welcome-file>index.html</welcome-file> 6 <welcome-file>index.htm</welcome-file> 7 <welcome-file>index.jsp</welcome-file> 8 <welcome-file>default.html</welcome-file> 9 <welcome-file>default.htm</welcome-file> 10 <welcome-file>default.jsp</welcome-file> 11 </welcome-file-list> 12 <servlet><servlet-name>ServletTest</servlet-name> 13 <servlet-class>servlet.FirstServlet</servlet-class> 14 </servlet> 15 <servlet-mapping> 16 <servlet-name>ServletTest</servlet-name> 17 <url-pattern>/*</url-pattern> 18 </servlet-mapping> 19 </web-app>
index.jsp
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 = "/ServletTest/FirstServlet">get this first servlet</a> 11 </body> 12 </html>
如果在上面web.xml里面配置<url-pattern>/*</url-pattern>， 在瀏覽器輸入：直接匹配到Servlet
如果在上面web.xml里面配置<url-pattern>/</url-pattern>， 在瀏覽器輸入：可以看出匹配到index.jsp
正常在web.xml里面配置<url-pattern>/FirstServlet</url-pattern>，會先匹配到index.jsp
二、Servlet+JSP
直接加例子：
1 package com.ht.servlet; 2 3 public class AccountBean { 4 private String username; 5 private String password; 6 /** 7 * @return the username 8 */ 9 public String getUsername() { 10 return username; 11 } 12 /** 13 * @param username the username to set 14 */ 15 public void setUsername(String username) { 16 this.username = username; 17 } 18 /** 19 * @return the password 20 */ 21 public String getPassword() { 22 return password; 23 } 24 /** 25 * @param password the password to set 26 */ 27 public void setPassword(String password) { 28 this.password = password; 29 } 30 } 31 32 package com.ht.servlet; 33 34 import java.io.IOException; 35 36 import javax.servlet.ServletException; 37 import javax.servlet.annotation.WebServlet; 38 import javax.servlet.http.HttpServlet; 39 import javax.servlet.http.HttpServletRequest; 40 import javax.servlet.http.HttpServletResponse; 41 import javax.servlet.http.HttpSession; 42 43 /** 44 * Servlet implementation class AccountBean 45 */ 46 @WebServlet("/CheckAccount") 47 public class CheckAccount extends HttpServlet { 48 private static final long serialVersionUID = 1L; 49 50 /** 51 * @see HttpServlet#HttpServlet() 52 */ 53 public CheckAccount() { 54 super(); 55 // TODO Auto-generated constructor stub 56 } 57 58 /** 59 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) 60 */ 61 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 62 HttpSession sessionzxl = request.getSession(); 63 AccountBean account = new AccountBean(); 64 String username = request.getParameter("username"); 65 String pwd = request.getParameter("pwd"); 66 account.setPassword(pwd); 67 account.setUsername(username); 68 System.out.println("username :"+ username + " password :" + pwd); 69 if((username != null)&&(username.trim().equals("jspp"))) { 70 System.out.println("username is right!"); 71 if((pwd != null)&&(pwd.trim().equals("1"))) { 72 System.out.println("success"); 73 sessionzxl.setAttribute("account", account); 74 String login_suc = "success.jsp"; 75 response.sendRedirect(login_suc); 76 return; 77 } 78 } 79 System.out.println("fail!"); 80 String login_fail = "fail.jsp"; 81 response.sendRedirect(login_fail); 82 return; 83 } 84 85 /** 86 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) 87 */ 88 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 89 90 doGet(request, response); 91 } 92 93 }
登錄的jsp頁面如下Login.jsp
1 <%@ page language="java" contentType="text/html; charset=ISO-8859-1" 2 pageEncoding="UTF-8"%> 3 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 4 <% 5 String path = request.getContextPath(); 6 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; 7 %> 8 9 <html> 10 <head> 11 <base href="<%=basePath%>"> 12 <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> 13 <title>My JSP 'login.jsp' starting page</title> 14 </head> 15 <body> 16 This is my JSP page. <br> 17 <form action="login"> 18 username:<input type="text" name="username"><br> 19 password:<input type="password" name="pwd"><br> 20 <input type="submit" value="Submit"> 21 </form> 22 </body> 23 </html>
登錄成功界面如下success.jsp：
1 <%@ page language="java" contentType="text/html; charset=ISO-8859-1" 2 pageEncoding="UTF-8"%> 3 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 4 <%@ page import="com.ht.servlet.AccountBean"%> 5 6 <% 7 String path = request.getContextPath(); 8 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; 9 %> 10 11 <html> 12 <head> 13 <base href="<%=basePath%>"> 14 <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> 15 <title>My JSP 'success.jsp' starting page</title> 16 </head> 17 <body> 18 <%AccountBean account = (AccountBean)session.getAttribute("account");%> 19 username:<%= account.getUsername()%> <br> 20 password:<%= account.getPassword() %> <br> 21 basePath: <%=basePath%><br> 22 path:<%=path%><br> 23 </body> 24 </html>
登錄失敗的jsp頁面如下：fail.jsp
1 <%@ page language="java" contentType="text/html; charset=ISO-8859-1" 2 pageEncoding="UTF-8"%> 3 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 4 <% 5 String path = request.getContextPath(); 6 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; 7 %> 8 9 <html> 10 <head> 11 <base href="<%=basePath%>"> 12 <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> 13 <title>My JSP 'fail.jsp' starting page</title> 14 </head> 15 <body> 16 Login Failed! <br> 17 basePath: <%=basePath%><br> 18 path:<%=path%><br> 19 </body> 20 </html>
web.xml配置如下：
1 <?xml version="1.0" encoding="UTF-8"?> 2 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0"> 3 <display-name>ServletTest</display-name> 4 <welcome-file-list> 5 <welcome-file>Login.jsp</welcome-file> 6 </welcome-file-list> 7 8 <servlet> 9 <description>This is the description of my J2EE component</description> 10 <display-name>This is the display name of my J2EE component</display-name> 11 <servlet-name>CheckAccount</servlet-name> 12 <servlet-class>com.ht.servlet.CheckAccount</servlet-class> 13 </servlet> 14 <servlet-mapping> 15 <servlet-name>CheckAccount</servlet-name> 16 <url-pattern>/login</url-pattern> 17 </servlet-mapping> 18 </web-app>
描述一下上面運行過程：
在瀏覽器輸入：http://localhost:8080/ServletTest/ 會通過歡迎頁面welcome-file-list找到登錄頁面Login.jsp, 界面顯示如下：
在登錄頁面輸入用戶名和密碼，點擊登錄，找到對應的action, 會去運行/login其對應的servlet, 找到doGet()方法，判斷用戶名和密碼
如果用戶名密碼不是jspp和1，就會跳轉到失敗頁面fail.jsp
如果用戶名等於jspp和1，則跳轉到成功頁面success.jsp
Session
上面就是一個最簡單的JSP和servlet例子。在運行上面例子中，有一個概念session.
在checkAccount.java中，直接通過request獲取session
HttpSession sessionzxl = request.getSession();
后面將定義的變量存儲到session中：sessionzxl.setAttribute("account", account);
在jsp中怎么獲取session？
在success.jsp中，有這么一行<%AccountBean account = (AccountBean)session.getAttribute("account");%>，那么session來至於哪兒？
查看資料后得知，session是jsp隱式對象。
JSP隱式對象是JSP容器為每個頁面提供的Java對象，開發者可以直接使用它們而不用顯式聲明。JSP隱式對象也被稱為預定義變量。
JSP所支持的九大隱式對象：
| 對象 | 描述 |
|---|---|
| request | HttpServletRequest 接口的實例 |
| response | HttpServletResponse 接口的實例 |
| out | JspWriter類的實例，用於把結果輸出至網頁上 |
| session | HttpSession類的實例 |
| application | ServletContext類的實例，與應用上下文有關 |
| config | ServletConfig類的實例 |
| pageContext | PageContext類的實例，提供對JSP頁面所有對象以及命名空間的訪問 |
| page | 類似於Java類中的this關鍵字 |
| Exception | Exception類的對象，代表發生錯誤的JSP頁面中對應的異常對象 |
session是jsp的內置對象，所以你可以直接寫在jsp的 <% session.setAttribute("a", b); //把b放到session里，命名為a， String M = session.getAttribute(“a”).toString(); //從session里把a拿出來，並賦值給M %>
下節添加一個Servlet+jsp+SQL例子。
https://blog.csdn.net/superit401/article/details/51974409