Servlet+JSP例子

前面两节已经学习了什么是Servlet,Servlet接口函数是哪些、怎么运行、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中新建一个Servlet工程项目。 今天这里主要是创建一个Servlet+JSP的例子。

一、学习之前补充一下web.xml中配置问题

web.xml中<welcome-file-list>配置（（web欢迎页、首页））

用于当用户在url中输入工程名称或者输入web容器url（如http://localhost:8080/）时直接跳转的页面.

welcome-file-list的工作原理是，按照welcome-file的.list一个一个去检查是否web目录下面存在这个文件，如果存在，继续下面的工作（或者跳转到index.html页面，或者配置有struts的，会直接struts的过滤工作）.如上例，先去webcontent(这里是Eclipse的工程目录根目录)下是否真的存在index.html这个文件，如果不存在去找是否存在index.jsp这个文件，以此类推。

还要说的是welcome-file不一定是html或者jsp等文件，也可以是直接访问一个action。就像我上面配置的一样，但要注意的是，一定要在webcontent下面建立一个index.action的空文件，然后使用struts配置去跳转，不然web找不到index.action这个文件，会报404错误，

如果配置了servlet的url-pattern是/*，那么访问localhost:8080/会匹配到该servlet上，而不是匹配welcome-file-list；如果url-pattern是/（该servlet即为默认servlet），如果其他匹配模式都没有匹配到，则会匹配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("处理get()的请求。。。");
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>， 在浏览器输入：直接匹配到Servlet

如果在上面web.xml里面配置<url-pattern>/</url-pattern>， 在浏览器输入：可以看出匹配到index.jsp

正常在web.xml里面配置<url-pattern>/FirstServlet</url-pattern>，会先匹配到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 }

登录的jsp页面如下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>

登录成功界面如下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>

 登录失败的jsp页面如下：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>

描述一下上面运行过程：

在浏览器输入：http://localhost:8080/ServletTest/     会通过欢迎页面welcome-file-list找到登录页面Login.jsp, 界面显示如下：

在登录页面输入用户名和密码，点击登录，找到对应的action, 会去运行/login其对应的servlet, 找到doGet()方法，判断用户名和密码

如果用户名密码不是jspp和1，就会跳转到失败页面fail.jsp

如果用户名等于jspp和1，则跳转到成功页面success.jsp

Session

上面就是一个最简单的JSP和servlet例子。在运行上面例子中，有一个概念session.

在checkAccount.java中，直接通过request获取session

HttpSession sessionzxl = request.getSession();

后面将定义的变量存储到session中：sessionzxl.setAttribute("account", account);

在jsp中怎么获取session？

在success.jsp中，有这么一行<%AccountBean account = (AccountBean)session.getAttribute("account");%>，那么session来至于哪儿？

查看资料后得知，session是jsp隐式对象。

JSP隐式对象是JSP容器为每个页面提供的Java对象，开发者可以直接使用它们而不用显式声明。JSP隐式对象也被称为预定义变量。

JSP所支持的九大隐式对象：

对象描述
request HttpServletRequest 接口的实例
response HttpServletResponse 接口的实例
out JspWriter类的实例，用于把结果输出至网页上
session HttpSession类的实例
application ServletContext类的实例，与应用上下文有关
config ServletConfig类的实例
pageContext PageContext类的实例，提供对JSP页面所有对象以及命名空间的访问
page 类似于Java类中的this关键字
Exception Exception类的对象，代表发生错误的JSP页面中对应的异常对象 
    session是jsp的内置对象，所以你可以直接写在jsp的  
    <%  
    session.setAttribute("a",  b);  //把b放到session里，命名为a，  
    String M = session.getAttribute(“a”).toString(); //从session里把a拿出来，并赋值给M  
    %>


下节添加一个Servlet+jsp+SQL例子。

https://blog.csdn.net/superit401/article/details/51974409

【推广】 免费学中医，健康全家人
原文地址：https://www.cnblogs.com/beilou310/p/10471836.html