JavaWeb--MVC设计模式
MVC是Model-View-Controller的简称，即模型-视图-控制器。
MVC是一种设计模式，它把应用程序分成三个核心模块：模型、视图、控制器，它们各自处理自己的任务。
关于 MVC：
M: Model. Dao
V: View. JSP, 在页面上填写 Java 代码实现显示
C: Controller. Serlvet:
受理请求
获取请求参数
调用 DAO 方法
可能会把 DAO 方法的返回值放入 request 中
转发（或重定向）页面
什么时候转发，什么时候重定向 ？ 若目标的响应页面不需要从 request 中读取任何值，则可以使用重定向。（还可以防止表单的重复提交）
不足：
使用数据库连接池，DBUtils，JDBCUtils 工具类，DAO 基类
一个请求一个 Serlvet 不好！一个模块使用一个 Serlvet，即多个请求可以使用一个 Servlet
在页面上加入 jQuery 提示
1.配置web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
version="3.1">
<servlet>
<!--<description></description>
<display-name>ListAllStudentsServlet</display-name>-->
<servlet-name>ListAllStudentsServlet</servlet-name>
<servlet-class>Javaweb_MVCTest.ListAllStudentsServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ListAllStudentsServlet</servlet-name>
<url-pattern>/listAllStudents</url-pattern>
</servlet-mapping>
</web-app>
2.写test.jsp
1 <%-- 2 Created by IntelliJ IDEA. 3 User: Skye 4 Date: 2017/12/7 5 Time: 15:26 6 To change this template use File | Settings | File Templates. 7 --%> 8 <%@ page contentType="text/html;charset=UTF-8" language="java" %> 9 <html> 10 <head> 11 <title>Title</title> 12 </head> 13 <body> 14 <a href="listAllStudents">List All Students</a> //超链接，里面的listAllStudents指向web.xml中
15 的listAllStudents，即ListAllStudentsServlet的Java文件
16 </body>
17 </html>
3.编写Student类
1 package Javaweb_MVCTest; 2 3 public class Student { 4 5 private int flowId; 6 private int type; 7 private String idCard; 8 private String examCard; 9 private String studentName; 10 private String location; 11 private int grade; 12 13 public int getFlowId() { 14 return flowId; 15 } 16 17 public void setFlowId(int flowId) { 18 this.flowId = flowId; 19 } 20 21 public int getType() { 22 return type; 23 } 24 25 public void setType(int type) { 26 this.type = type; 27 } 28 29 public String getIdCard() { 30 return idCard; 31 } 32 33 public void setIdCard(String idCard) { 34 this.idCard = idCard; 35 } 36 37 public String getExamCard() { 38 return examCard; 39 } 40 41 public void setExamCard(String examCard) { 42 this.examCard = examCard; 43 } 44 45 public String getStudentName() { 46 return studentName; 47 } 48 49 public void setStudentName(String studentName) { 50 this.studentName = studentName; 51 } 52 53 public String getLocation() { 54 return location; 55 } 56 57 public void setLocation(String location) { 58 this.location = location; 59 } 60 61 public int getGrade() { 62 return grade; 63 } 64 65 public void setGrade(int grade) { 66 this.grade = grade; 67 } 68 69 public Student(int flowId, int type, String idCard, String examCard, String studentName, String location, int grade) { 70 this.flowId = flowId; 71 this.type = type; 72 this.idCard = idCard; 73 this.examCard = examCard; 74 this.studentName = studentName; 75 this.location = location; 76 this.grade = grade; 77 } 78 79 public Student() { //为了使用反射 80 } 81 }
4.建立数据库连接，读取数据（编写StudentDAO）
1 package Javaweb_MVCTest; 2 3 import java.sql.*; 4 import java.util.ArrayList; 5 import java.util.List; 6 7 public class StudentDAO { 8 9 public List<Student> getAll(){ 10 11 List<Student> students = new ArrayList<>(); 12 13 Connection connection = null; 14 PreparedStatement preparedStatement = null; 15 ResultSet resultSet = null; 16 17 try{ 18 String driverClass = "com.mysql.jdbc.Driver"; 19 String url = "jdbc:mysql://localhost:3306/db_person"; 20 String user = "root"; 21 String password = "1234"; 22 23 Class.forName(driverClass); 24 connection = DriverManager.getConnection(url, user, password); 25 26 String sql = "SELECT flow_id, type, id_card, exam_card, student_name, location, grade FROM examstudent"; 27 28 preparedStatement = connection.prepareStatement(sql); 29 30 // preparedStatement.executeUpdate(); 31 resultSet = preparedStatement.executeQuery(); 32 33 while(resultSet.next()){ 34 int flowId = resultSet.getInt(1); 35 int type = resultSet.getInt(2); 36 String idCard = resultSet.getString(3); 37 String examCard = resultSet.getString(4); 38 String studentName = resultSet.getString(5); 39 String location = resultSet.getString(6); 40 int grade = resultSet.getInt(7); 41 42 Student student = new Student(flowId, type, idCard, examCard, studentName, location, grade); 43 44 students.add(student); 45 46 } 47 48 } catch (Exception e) { 49 e.printStackTrace(); 50 }finally{ 51 if(resultSet != null){ 52 try { 53 resultSet.close(); 54 } catch (SQLException e1) { 55 e1.printStackTrace(); 56 } 57 } 58 if(preparedStatement != null){ 59 try { 60 preparedStatement.close(); 61 } catch (SQLException e1) { 62 e1.printStackTrace(); 63 } 64 } 65 if(connection != null){ 66 try { 67 connection.close(); 68 } catch (SQLException e1) { 69 e1.printStackTrace(); 70 } 71 } 72 } 73 return students; 74 } 75 76 }
5.调用4的结果（ListAllStudentsServlet）
1 package Javaweb_MVCTest; 2 3 import javax.servlet.ServletException; 4 import javax.servlet.http.HttpServlet; 5 import javax.servlet.http.HttpServletRequest; 6 import javax.servlet.http.HttpServletResponse; 7 import java.io.IOException; 8 import java.util.Arrays; 9 import java.util.List; 10 11 public class ListAllStudentsServlet extends HttpServlet { 12 13 private static final long serialVersionUID = 1L; 14 @Override 15 protected void doGet(HttpServletRequest req, HttpServletResponse resp) 16 throws ServletException, IOException { 17 //super.doGet(req, resp); 18 19 StudentDAO studentDAO = new StudentDAO(); 20 List<Student> students = studentDAO.getAll(); 21 22 req.setAttribute("students", students);//把students这个对象保存在req作用域中，在转发进入的页面就能直接获取 23 24 req.getRequestDispatcher("/students.jsp").forward(req, resp);//请求转发 25 } 26 }
）
