model1开发模式
- 工作流程：
①浏览器请求，JSP页面接收
②JSP根据请求和JavaBean进行交互
③JavaBean进行业务处理，JDBC操纵数据库
④JSP将请求结果返回浏览器页面
- JSP的理解
JSP是servlet的简化版本，jsp引擎会将jsp编译为servlet，再对servlet进行编译
- 利用model1，设计一个简单的登陆页面
新建Java web项目，项目结构如下：
建立基于Mysql的JDBC类
1 package com.ddpapa.test.jdbc; 2 3 import java.sql.Connection; 4 import java.sql.DriverManager; 5 import java.sql.ResultSet; 6 import java.sql.SQLException; 7 import java.sql.Statement; 8 9 public class MysqlDBConn { 10 private Statement stmt; 11 private Connection conn; 12 ResultSet rs; 13 public MysqlDBConn(){ 14 stmt = null; 15 try { 16 /*加载数据库驱动获取数据库连接*/ 17 Class.forName("com.mysql.jdbc.Driver"); 18 conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/datatest","root","123456"); 19 } catch (Exception e) { 20 // TODO: handle exception 21 e.printStackTrace(); 22 } 23 rs = null; 24 } 25 public Connection getConn() { 26 return this.conn; 27 } 28 public ResultSet executeQuery(String sql){ 29 /*取得结果集*/ 30 try { 31 stmt = conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_UPDATABLE); 32 rs = stmt.executeQuery(sql); 33 } catch (Exception e) { 34 // TODO: handle exception 35 System.err.println("Data.executeQuery: " + e.getMessage()); 36 } 37 return rs; 38 } 39 public void closeStmt() 40 { 41 /*关闭Stmt*/ 42 try 43 { 44 stmt.close(); 45 }catch(SQLException e){ 46 System.err.println("Data.executeQuery: " + e.getMessage()); 47 } 48 } 49 public void closeConn() 50 { 51 /*关闭数据库连接*/ 52 try 53 { 54 conn.close(); 55 }catch(SQLException e){ 56 System.err.println("Data.executeQuery: " + e.getMessage()); 57 } 58 } 59 60 }
建立JavaBean
1 package com.ddpapa.test.model.vo; 2 3 public class UserTable { 4 private Integer id; 5 private String username; 6 private String password; 7 public Integer getId() { 8 return id; 9 } 10 public void setId(Integer id) { 11 this.id = id; 12 } 13 public String getUsername() { 14 return username; 15 } 16 public void setUsername(String username) { 17 this.username = username; 18 } 19 public String getPassword() { 20 return password; 21 } 22 public void setPassword(String password) { 23 this.password = password; 24 } 25 26 }
新建login.jsp
1 <%@ page language="java" pageEncoding="gb2312" %> 2 <html> 3 <head> 4 <title>登陆界面title> 5 head> 6 <body> 7 <form action="validate.jsp" method="get"> 8 <table> 9 <tr> 10 <th colspan="2" align="center">登陆页面th> 11 tr> 12 <tr> 13 <td>用户名：td> 14 <td><input type="text" name="username" size="20">td> 15 tr> 16 <tr> 17 <td>密码：td> 18 <td><input type="password" name="password" size="20">td> 19 tr> 20 table> 21 <input type="submit" value="登陆"> 22 <input type="reset" value="重置"> 23 form> 24 body> 25 html>
新建validate.jsp
1 <%@page language="java" pageEncoding="gb2312" import="java.sql.*,com.ddpapa.test.model.vo.UserTable"%> 2 <jsp:useBean id="MysqlDB" scope="page" class="com.ddpapa.test.jdbc.MysqlDBConn">jsp:useBean> 3 <html> 4 <head> 5 <meta http-equiv="Content-Type" content="text/html;charset=gb2312"> 6 head> 7 <body> 8 <% 9 request.setCharacterEncoding("gb2312"); 10 String usr=request.getParameter("username"); 11 String pwd=request.getParameter("password"); 12 boolean validate = false; 13 UserTable user = null; 14 user = (UserTable)session.getAttribute("user"); 15 if(user==null){ 16 String sql = "select * from userTable"; 17 ResultSet rs = MysqlDB.executeQuery(sql); //取得结果集 18 while(rs.next()){ 19 if((rs.getString("username").trim().compareTo(usr)==0) && (rs.getString("password").compareTo(pwd)==0)){ 20 user = new UserTable(); 21 user.setId(rs.getInt(1)); 22 user.setUsername(rs.getString(2)); 23 user.setPassword(rs.getString(3)); 24 validate = true; 25 } 26 } 27 rs.close(); 28 MysqlDB.closeStmt(); 29 MysqlDB.closeConn(); 30 }else{ 31 validate = true; 32 } 33 if(validate){ 34 %> 35 <jsp:forward page="success.jsp"/> 36 <% 37 }else{ 38 %> 39 <jsp:forward page="error.jsp"/> 40 <% 41 } 42 %> 43 body> 44 html>
新建error.jsp
1 <%@ page language="java" pageEncoding="gb2312" %> 2 <html> 3 <head> 4 <title>登陆失败title> 5 head> 6 <body> 7 抱歉！登陆失败 8 body> 9 html>
新建success.jsp
1 <%@ page language="java" pageEncoding="gb2312" import="com.ddpapa.test.model.vo.UserTable"%> 2 <html> 3 <head> 4 <title>登陆成功title> 5 head> 6 <body> 7 <% 8 String usr = request.getParameter("username"); 9 %> 10 <%=usr%>,您好！欢迎登陆。 11 body> 12 html>
修改web.xml配置文件
1 xml version="1.0" encoding="UTF-8"?> 2 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" version="3.1"> 3 <display-name>jsp_model1display-name> 4 <welcome-file-list> 5 <welcome-file>login.jspwelcome-file> 6 welcome-file-list> 7 web-app>
- 错误集锦
500错误——lib目录下缺少数据库连接jar包
500错误——org.apache.jasper.JasperException:An exception occurred processing JSP page [/xxx.jsp] at line [x]
success代码如下时出现错误：
错误原因session对象getAttribute返回值为null（根本原因user不存在），导致空指针错误，改为request对象解决问题
model2开发模式
- 工作流程
①浏览器请求，servlet接收到请求和JavaBean进行交互
②JavaBean进行业务处理，通过JDBC完成与数据库交互
③servlet将将请求结果给JSP
④JSP以页面形式展示给浏览器
- 在model1的基础上利用model2设计登陆
项目结构如下：
新建MainServlet.java文件（选择新建servlet即可自动生成doGet和doPost方法），代码如下：
1 package com.ddpapa.test.model.servlet; 2 3 import java.io.IOException; 4 import java.sql.ResultSet; 5 import java.sql.SQLException; 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 import javax.servlet.http.HttpSession; 12 13 import com.ddpapa.test.jdbc.MysqlDBConn; 14 import com.ddpapa.test.model.vo.UserTable; 15 16 public class MainServlet extends HttpServlet { 17 public MainServlet() { 18 super(); 19 } 20 public void doGet(HttpServletRequest request, HttpServletResponse response) 21 throws ServletException, IOException { 22 request.setCharacterEncoding("gb2312"); 23 String usr=request.getParameter("username"); 24 String pwd=request.getParameter("password"); 25 boolean validate = false; 26 HttpSession session = request.getSession(); 27 UserTable user = null; 28 user = (UserTable)session.getAttribute("user"); 29 MysqlDBConn MysqlDB = new MysqlDBConn(); 30 if(user==null){ 31 String sql = "select * from userTable"; 32 ResultSet rs = MysqlDB.executeQuery(sql); //取得结果集 33 try { 34 while(rs.next()){ 35 if((rs.getString("username").trim().compareTo(usr)==0) && (rs.getString("password").compareTo(pwd)==0)){ 36 user = new UserTable(); 37 user.setId(rs.getInt(1)); 38 user.setUsername(rs.getString(2)); 39 user.setPassword(rs.getString(3)); 40 validate = true; 41 } 42 } 43 } catch (SQLException e) { 44 // TODO Auto-generated catch block 45 e.printStackTrace(); 46 } 47 try { 48 rs.close(); 49 } catch (SQLException e) { 50 // TODO Auto-generated catch block 51 e.printStackTrace(); 52 } 53 MysqlDB.closeStmt(); 54 MysqlDB.closeConn(); 55 }else{ 56 validate = true; 57 } 58 if(validate){ 59 response.sendRedirect("/jsp_model2/success.jsp"); 60 }else{ 61 response.sendRedirect("/jsp_model2/error.jsp"); 62 } 63 } 64 public void doPost(HttpServletRequest request, HttpServletResponse response) 65 throws ServletException, IOException { 66 doGet(request, response); 67 } 68 69 }
修改web.xml文件，代码如下：
1 xml version="1.0" encoding="UTF-8"?> 2 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1"> 3 <display-name>jsp_model2display-name> 4 <servlet> 5 <servlet-name>MainServletservlet-name> 6 <servlet-class>com.ddpapa.test.model.servlet.MainServletservlet-class> 7 servlet> 8 9 <servlet-mapping> 10 <servlet-name>MainServletservlet-name> 11 <url-pattern>/servlet/MainServleturl-pattern> 12 servlet-mapping> 13 <welcome-file-list> 14 <welcome-file>login.jspwelcome-file> 15 welcome-file-list> 16 web-app>
修改login.jsp并删除valitade.jsp文件，代码如下：
1 <%@ page language="java" pageEncoding="gb2312" %> 2 <html> 3 <head> 4 <title>登陆界面title> 5 head> 6 <body> 7 <form action="servlet/MainServlet" method="get"> 8 <table> 9 <tr> 10 <th colspan="2" align="center">登陆页面th> 11 tr> 12 <tr> 13 <td>用户名：td> 14 <td><input type="text" name="username" size="20">td> 15 tr> 16 <tr> 17 <td>密码：td> 18 <td><input type="password" name="password" size="20">td> 19 tr> 20 table> 21 <input type="submit" value="登陆"> 22 <input type="reset" value="重置"> 23 form> 24 body> 25 html>
错误集锦：
login.jsp中的action没有和servlet中的url-pattern匹配上
servlet中的url-pattern匹配问题参考：
https://www.cnblogs.com/canger/p/6084846.html
https://blog.csdn.net/jarniyy/article/details/74295802