Servlet服务连接器。
Servlet（Server Applet）是Java Servlet的简称，称为小服务程序或服务连接器，用Java编写的服务器端程序，具有独立于平台和协议的特性，主要功能在于交互式地浏览和生成数据，生成动态Web内容。
在Java Web工程中找到WebRoot，会发现里面有一个index.jsp网页。
（可以自己创建一个页面）注：常用 pageEncoding="UTF-8"
- jsp 指令<%%> 脚本 表达式<%=%>
实现过程：
Servlet类：
package com.servlet;
import java.util.List;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.Impl.UserImpl;
import com.bao.UserInterface;
import com.pojo.User;
public class UserServlet extends HttpServlet {
public UserServlet() {
super();
}
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}
public void doGet(HttpServletRequest request, HttpServletResponse response){
}
//接口：接收数据和跳转页面
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
System.out.println("dopost");
//确定编码
request.setCharacterEncoding("utf-8");
//接值,参数必须和login中(用户名和密码)input标签中的name值一样
String username = request.getParameter("username");
String password = request.getParameter("password");
System.out.println("用户名:"+username+",密码:"+password);
User u = new User();
u.setUsername(username);
u.setPassword(password);
//调用接口-多态 指向实现类
UserInterface uif = new UserImpl();
boolean bool = uif.loginSelect(u);
//跳转页面
//转发 转向 ： 服务器一次请求 最终浏览器地址停留在请求名上(刷新一次就向数据库添加一次数据)
//重定向 ： 服务器两次请求 最终浏览器地址停留在jsp页面上 容易丢值
if(bool){
List<User> list = uif.selectUserAll();
//利用session 作用域向页面传值HttpSession
request.getSession().setAttribute("userlist", list);
//重定向
response.sendRedirect(request.getContextPath()+"/userlist.jsp");
}else{
//转发
request.getRequestDispatcher("/loginfail.jsp").forward(request, response);
}
}
public void init() throws ServletException {
// Put your code here
}
}实现类：
public boolean loginSelect(User u) {
try {
Connection conn = DBUtil.getConnetion();
String sql = "select * from users where username=? and password=?";
PreparedStatement ps = conn.prepareStatement(sql);
ps.setString(1, u.getUsername());
ps.setString(2, u.getPassword());
ResultSet rs = ps.executeQuery();
if(rs.next()){
return true;
}else{
return false;
}
} catch (Exception e) {
e.printStackTrace();
return false;
}
}jsp页面：login.jsp（登录页面）
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>login</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<div align="center">
<!-- url-pattern中的路径 -->
<form action="servlet/UserServlet" method="post">
用户名：<input type = "text" name = "username"/><br>
密码：<input type = "password" name = "password"/>
<input type = "submit" name = "登录"/>
</form>
</div>
</body>
</html>userlist.jsp：（点击登录以后跳转到这个页面，这个页面上显示出所有数据）
注意要写：<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix = "c" %>这一句
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix = "c" %>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'userlist.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<div align = "center">
<table border = "1" >
<tr>
<td>Id</td>
<td>用户名</td>
<td>密码</td>
<td>年龄</td>
</tr>
<!-- EL表达式 前台页面接值 ：作用域 session(一次会话) 只要不关闭浏览器，信息就保存在session里
request response page (jsp内置对象)-->
<c:forEach items="${userlist}" var="list">
<tr>
<td>${list.id}</td>
<td>${list.username}</td>
<td>${list.password}</td>
<td>${list.age}</td>
</tr>
</c:forEach>
</table>
</div>
</body>
</html>web.xml：（在WebRoot->WEB-INF中）主要是来查找url-pattern写进login的action中
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<display-name></display-name>
<servlet>
<servlet-name>UserServlet</servlet-name>
<servlet-class>com.servlet.UserServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>UserServlet</servlet-name>
<url-pattern>/servlet/UserServlet</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>流程：
- 前台用户填写信息
- 后台接收登录信息 servlet
- 利用接取到的数据进行数据库查询 (用户点登陆->通过action路径到web.xml->找到servlet-mapping标签，在里面找到servlet-name
- 在servlet中找到和刚才那个servlet-name一样的->根据class路径找到Servlet类，进行数据接收)
一系列完整页面：
1.web.xml
（主要是可以找到其中各种Servlet类的地址，应用于form action中）
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<display-name></display-name>
<servlet>
<servlet-name>UserServlet</servlet-name>
<servlet-class>com.servlet.UserServlet</servlet-class>
</servlet>
<servlet>
<description>This is the description of my J2EE component</description>
<display-name>This is the display name of my J2EE component</display-name>
<servlet-name>UserAddServlet</servlet-name>
<servlet-class>com.servlet.UserAddServlet</servlet-class>
</servlet>
<servlet>
<description>This is the description of my J2EE component</description>
<display-name>This is the display name of my J2EE component</display-name>
<servlet-name>UserUpdateServlet</servlet-name>
<servlet-class>com.servlet.UserUpdateServlet</servlet-class>
</servlet>
<servlet>
<description>This is the description of my J2EE component</description>
<display-name>This is the display name of my J2EE component</display-name>
<servlet-name>UserUpdate2Servlet</servlet-name>
<servlet-class>com.servlet.UserUpdate2Servlet</servlet-class>
</servlet>
<servlet>
<description>This is the description of my J2EE component</description>
<display-name>This is the display name of my J2EE component</display-name>
<servlet-name>UserDeleteServlet</servlet-name>
<servlet-class>com.servlet.UserDeleteServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>UserServlet</servlet-name>
<url-pattern>/servlet/UserServlet</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>UserAddServlet</servlet-name>
<url-pattern>/servlet/UserAddServlet</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>UserUpdateServlet</servlet-name>
<url-pattern>/servlet/UserUpdateServlet</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>UserUpdate2Servlet</servlet-name>
<url-pattern>/servlet/UserUpdate2Servlet</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>UserDeleteServlet</servlet-name>
<url-pattern>/servlet/UserDeleteServlet</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>2.主要页面
【login.jsp】
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>login</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
</head>
<body>
<div align="center">
<!-- url-pattern中的路径 -->
<form action="servlet/UserServlet" method="post">
用户名：<input type = "text" name = "username"/><br>
密码：<input type = "password" name = "password"/>
<input type = "submit" name = "登录"/>
</form>
</div>
</body>
</html>【userlist.jsp】
(这个页面主要是用来显示数据信息，然后可以进行编辑和删除)
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix = "c" %>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'userlist.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<div align = "center">
<table border = "1" >
<tr>
<td>Id</td>
<td>用户名</td>
<td>密码</td>
<td>年龄</td>
<td>编辑</td>
<td>删除</td>
</tr>
<!-- EL表达式 前台页面接值 ：作用域 session(一次会话) 只要不关闭浏览器，信息就保存在session里
request response page (jsp内置对象)-->
<c:forEach items="${userlist}" var="list">
<tr>
<td>${list.id}</td>
<td>${list.username}</td>
<td>${list.password}</td>
<td>${list.age}</td>
<!-- get方法提交 -->
<td><a href="servlet/UserUpdateServlet?id=${list.id}">编辑</a></td>
<td><a href="servlet/UserDeleteServlet?id=${list.id}">删除</a></td>
</tr>
</c:forEach>
</table>
<a href="useradd.jsp">增加</a>
</div>
</body>
</html>【update.jsp】
（这个页面是修改页面，需要把数据都显示出来，然后修改后进行提交。）
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'update.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<div align="center">
<!-- url-pattern中的路径 -->
<form action="servlet/UserUpdate2Servlet" method="post">
<input type="hidden" name = "id" value="${user.id}"/>
用户名：<input type = "text" name = "username" value="${user.username}"/><br>
密码：<input type = "text" name = "password" value="${user.password}"/><br>
年龄：<input type = "text" name="age" value="${user.age}"/>
<input type = "submit" name = "提交"/>
</form>
</div>
</body>
</html>【useradd.jsp】
（这个是增加一条数据的页面）
（其实和login几乎一模一样，除了对应的Servlet位置不同）
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'useradd.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<div align="center">
<!-- url-pattern中的路径 -->
<form action="servlet/UserAddServlet" method="post">
用户名：<input type = "text" name = "username"/><br>
密码：<input type = "password" name = "password"/><br>
年龄：<input type = "text" name="age"/>
<input type = "submit" name = "提交"/>
</form>
</div>
</body>
</html>3.Servlet类
仅贴出主要部分代码，有关于User类和UserInterface和UserImpl在之前的JDBC中有写，这里不再给出代码。
【UserServlet】
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
System.out.println("dopost");
//确定编码
request.setCharacterEncoding("utf-8");
//接值,参数必须和login中(用户名和密码)input标签中的name值一样
String username = request.getParameter("username");
String password = request.getParameter("password");
System.out.println("用户名:"+username+",密码:"+password);
User u = new User();
u.setUsername(username);
u.setPassword(password);
//调用接口-多态 指向实现类
UserInterface uif = new UserImpl();
boolean bool = uif.loginSelect(u);
if(bool){
List<User> list = uif.selectUserAll();
//利用session 作用域向页面传值HttpSession
request.getSession().setAttribute("userlist", list);
//重定向
response.sendRedirect(request.getContextPath()+"/userlist.jsp");
}else{
//转发
request.getRequestDispatcher("/loginfail.jsp").forward(request, response);
}
}【UserAddServlet】
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//字符编码
request.setCharacterEncoding("utf-8");
String username = request.getParameter("username");
String password = request.getParameter("password");
int age = Integer.parseInt(request.getParameter("age"));
User user = new User();
user.setAge(age);
user.setPassword(password);
user.setUsername(username);
UserInterface uif = new UserImpl();
uif.addUser(user);
List<User> list = uif.selectUserAll();
//利用session 作用域向页面传值HttpSession
request.getSession().setAttribute("userlist", list);
//重定向
response.sendRedirect(request.getContextPath()+"/userlist.jsp");
}【UserUpdateServlet】
注：这里是用的doGet方法，至于doGet和doPost有什么不同：（直接参考：https://www.cnblogs.com/alsf/p/9133951.html)
1.当form框里面的method为get时，执行doGet方法
当form框里面的method为post时，执行doPost方法
2.数据传送方式：
get方式：表单数据存放在URL地址后面。所有get方式提交时HTTP中没有消息体。
post方式：表单数据存放在HTTP协议的消息体中以实体的方式传送到服务器。
3.get是把参数数据队列加到提交表单的ACTION属性所指的URL中，值和表单内各个字段一一对应，在URL中可以看到。
post是通过HTTP post机制，将表单内各个字段与其内容放置在HTML HEADER内一起传送到ACTION属性所指的URL地址。用户看不到这个过程。
4.GET方式：数据量长度有限制，一般不超过2kb。因为是参数传递，且在地址栏中，故数据量有限制。
POST方式：适合大规模的数据传送。因为是以实体的方式传送的。
5.GET方式：安全性差。因为是直接将数据显示在地址栏中，浏览器有缓冲，可记录用户信息。所以安全性低。
POST方式：安全性高。因为post方式提交数据时是采用的HTTP post机制，是将表单中的字段与值放置在HTTP HEADER内一起传送到ACTION所指的URL中，用户是看不见的。
6.在做数据查询时，建议用Get方式；而在做数据添加、修改或删除时，建议用Post方式。
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setCharacterEncoding("utf-8");
int id = Integer.parseInt(request.getParameter("id"));
UserInterface uif = new UserImpl();
User user = uif.selectUserById(id);
request.getSession().setAttribute("user", user);
response.sendRedirect(request.getContextPath()+"/update.jsp");
}【UserUpdate2Servlet】
为什么有两个update呢？第一个是userlist超链接“编辑”所使用到的Servlet，第二个是表单提交以后所使用的到的Servlet。
两个超链接“编辑”和“删除”对应的Servlet是doGet方法，其余为doPost。
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setCharacterEncoding("utf-8");
int id = Integer.parseInt(request.getParameter("id"));
String username = request.getParameter("username");
String password = request.getParameter("password");
int age = Integer.parseInt(request.getParameter("age"));
User user = new User();
user.setAge(age);
user.setId(id);
user.setUsername(username);
user.setPassword(password);
UserInterface uif = new UserImpl();
uif.updateUser(user);
List<User> list = uif.selectUserAll();
//利用session 作用域向页面传值HttpSession
request.getSession().setAttribute("userlist", list);
//重定向
response.sendRedirect(request.getContextPath()+"/userlist.jsp");
}【UserDeleteServlet】
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
System.out.println("doGet");
request.setCharacterEncoding("utf-8");
int id = Integer.parseInt(request.getParameter("id"));
UserInterface uif = new UserImpl();
uif.deleteUser(id);
List<User> list = uif.selectUserAll();
//利用session 作用域向页面传值HttpSession
request.getSession().setAttribute("userlist", list);
//重定向
response.sendRedirect(request.getContextPath()+"/userlist.jsp");
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