[原创]java WEB学习笔记19：初识MVC 设计模式：查询，删除练习(理解思想)，小结，问题

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1.在上一学习笔记中，了解了MVC设计的思想，这一学习笔记，主要手动写一个MVC的查询程序，比较糙，重理解思想。

2.需求：通过index.jsp 页面发过请求，查询学生的信息，将学生的信息输出到des.jsp页面上；可以删除学生的信息。

3.代码结构

　　1）index.jsp : 一个查询的超链接页面；

　　2）des.jps : 显示查询的页面；

　　3）success.jsp :删除成功后跳转的页面

　　4）ListAllStudentsServlet.java　：　负责处理index 页面请求的servlet，同时与dao交互；

　　5）DeletStudentServlet.java ：通过传入的flowId 进行删除；

　　6）StudentDao.java : 定义方法getA() 用于与数据库交互，查询数据，返回结果；deleteByFlowId(int flowId)方法，按照flowId删除相应的学生信息；

　　7）Student.java ：bean 同数据库表的字段一致，get set方法，带参，不带餐构造器，用于检查的 toString 方法；

4.具体代码

　　1）index.jsp

 <%@ page language="java" contentType="text/html; charset=UTF-8"

     pageEncoding="UTF-8"%>

 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

 <html>

 <head>

 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

 <title>index</title>

 </head>

 <body>

     <a href="listAllStudents">List All Students</a>

 </body>

 </html>

　　2）des.jsp

 <%@ page language="java" contentType="text/html; charset=UTF-8"

     pageEncoding="UTF-8"%>

 <%@ page import="java.util.List"%>

 <%@ page import="com.jason.testMVC.Student"%>

 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

 <html>

 <head>

 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

 <title>des</title>

 </head>

 <body>

     <%

         List<Student> stus = (List<Student>) request

                 .getAttribute("students");

         if (stus == null) {

             System.out.println("stus is null");

         } else {

     %>

     <table border="1" cellpadding="10" cellspacing="0">

         <tr>

             <th>FlowId</th>

             <th>Type</th>

             <th>IdCard</th>

             <th>ExamCard</th>

             <th>StudentName</th>

             <th>Location</th>

             <th>Grade</th>

             <th>Delete</th>

         </tr>

         <%

             for (Student stu : stus) {

         %>

         <tr>

             <td><%=stu.getExamCard()%></td>

             <td><%=stu.getType()%></td>

             <td><%=stu.getIdCard()%></td>

             <td><%=stu.getExamCard()%></td>

             <td><%=stu.getStudentName()%></td>

             <td><%=stu.getLocation()%></td>

             <td><%=stu.getGrade()%></td>

             <td><a href="deletStudent?flowId=<%=stu.getFlowId() %>"/>Delete</td>   //通过这个种方式，向servlet传入flowId参数

         </tr>

         <%

                 }

             }

         %>

     </table>

 </body>

 </html>

　　3）success.jsp

 <%@ page language="java" contentType="text/html; charset=UTF-8"

     pageEncoding="UTF-8"%>

 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

 <html>

 <head>

 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

 <title>Insert title here</title>

 </head>

 <body>

     <h1>删除成功</h1>

     <a href="listAllStudents">List All Students</a>

 </body>

 </html>

　　4）ListAllStudentsServlet.java

 package com.jason.testMVC;

 import java.io.IOException;

 import java.util.List;

 import javax.servlet.ServletException;

 import javax.servlet.annotation.WebServlet;

 import javax.servlet.http.HttpServlet;

 import javax.servlet.http.HttpServletRequest;

 import javax.servlet.http.HttpServletResponse;

 /**

  * Servlet implementation class ListAllStudentsServlet

  */

 @WebServlet("/listAllStudents")

 public class ListAllStudentsServlet extends HttpServlet {

     private static final long serialVersionUID = 1L;

     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

             StudentDao studentDao = new StudentDao();

             List<Student>  students = studentDao.getAll();

             request.setAttribute("students", students);

             request.getRequestDispatcher("/students.jsp").forward(request, response);

     }

 }

　　5）DeletStudentServlet.java

 package com.jason.testMVC;

 import java.io.IOException;

 import javax.servlet.ServletException;

 import javax.servlet.annotation.WebServlet;

 import javax.servlet.http.HttpServlet;

 import javax.servlet.http.HttpServletRequest;

 import javax.servlet.http.HttpServletResponse;

 import com.sun.org.apache.xalan.internal.xsltc.compiler.sym;

 /**

  * Servlet implementation class DeletStudentServlet

  */

 @WebServlet("/deletStudent")

 public class DeletStudentServlet extends HttpServlet {

     private static final long serialVersionUID = 1L;

     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

         String flowIdStr =   request.getParameter("flowId");

 //    int flowId = Integer.parseInt(flowIdStr);

 //        System.out.println(flowIdStr);

         StudentDao  studentDao = new StudentDao();

         boolean flage = studentDao.deleteByFlowId(Integer.parseInt(flowIdStr));

         if(flage){

             request.getRequestDispatcher("/success.jsp").forward(request, response);

         }else{

             System.out.println("删除失败");

         }

     }

 }

　　6）StudentDao.java

 package com.jason.testMVC;

 import java.sql.Connection;

 import java.sql.DriverManager;

 import java.sql.PreparedStatement;

 import java.sql.ResultSet;

 import java.sql.SQLException;

 import java.util.ArrayList;

 import java.util.List;

 public class StudentDao {

     public List<Student> getAll() {

         List<Student> students = new ArrayList<Student>();

         Connection connection = null;

         PreparedStatement preparedStatement = null;

         ResultSet resultSet = null;

         try {

             String driverClass = "com.mysql.jdbc.Driver";

             String url = "jdbc:mysql://127.0.0.1:3306/atguigu";

             String user = "root";

             String password = "zhangzhen";

             // 加载驱动类

             Class.forName(driverClass);

             connection = DriverManager.getConnection(url, user, password);

             String sql = "SELECT *  FROM student";

             preparedStatement = connection.prepareStatement(sql);

             resultSet = preparedStatement.executeQuery();

             while (resultSet.next()) {

                 int FlowId = resultSet.getInt(1);

                 int type = resultSet.getInt(2);

                 String idCard = resultSet.getString(3);

                 String examCard = resultSet.getString(4);

                 String studentName = resultSet.getString(5);

                 String locatoin = resultSet.getString(6);

                 int grade = resultSet.getInt(7);

                 Student student = new Student(FlowId, type, idCard, examCard,

                         studentName, locatoin, grade);

                 students.add(student);

             }

         } catch (Exception e) {

             e.printStackTrace();

         } finally {

             // 关闭资源

             try {

                 if (resultSet != null) {

                     resultSet.close();

                 }

             } catch (SQLException e) {

                 e.printStackTrace();

             }

             try {

                 if (preparedStatement != null) {

                     preparedStatement.close();

                 }

             } catch (SQLException e) {

                 e.printStackTrace();

             }

             try {

                 if (connection != null) {

                     connection.close();

                 }

             } catch (SQLException e) {

                 e.printStackTrace();

             }

         }

         return students;

     }

     public boolean deleteByFlowId(int flowId){

         Connection connection = null;

         PreparedStatement preparedStatement = null;

         boolean  flage = false;

         try {

             String driverClass = "com.mysql.jdbc.Driver";

             String url = "jdbc:mysql://127.0.0.1:3306/atguigu";

             String user = "root";

             String password = "zhangzhen";

             // 加载驱动类

             Class.forName(driverClass);

             connection = DriverManager.getConnection(url, user, password);

             String sql = "DELETE  FROM student WHERE FlowID = ?";

             preparedStatement = connection.prepareStatement(sql);

             preparedStatement.setInt(1, flowId);

             int result = preparedStatement.executeUpdate();

             if(result >= 0){

                 flage = true;

             }

         } catch (Exception e) {

             e.printStackTrace();

         } finally {

             // 关闭资源

             try {

                 if (preparedStatement != null) {

                     preparedStatement.close();

                 }

             } catch (SQLException e) {

                 e.printStackTrace();

             }

             try {

                 if (connection != null) {

                     connection.close();

                 }

             } catch (SQLException e) {

                 e.printStackTrace();

             }

         }

         return flage;

     }

 }

　　6）Student.java

 package com.jason.testMVC;

 /**

  *

  * @author: jason

  * @time:2016年5月24日下午11:31:08

  * @description:

  */

 public class Student {

     private int flowId;

     private int type;

     private String idCard;

     private String examCard;

     private String studentName;

     private String location;

     private int grade;

     public Integer getFlowId() {

         return flowId;

     }

     public void setFlowId(Integer flowId) {

         this.flowId = flowId;

     }

     public int getType() {

         return type;

     }

     public void setType(int type) {

         this.type = type;

     }

     public String getIdCard() {

         return idCard;

     }

     public void setIdCard(String idCard) {

         this.idCard = idCard;

     }

     public String getExamCard() {

         return examCard;

     }

     public void setExamCard(String examCard) {

         this.examCard = examCard;

     }

     public String getStudentName() {

         return studentName;

     }

     public void setStudentName(String studentName) {

         this.studentName = studentName;

     }

     public String getLocation() {

         return location;

     }

     public void setLocation(String location) {

         this.location = location;

     }

     public int getGrade() {

         return grade;

     }

     public void setGrade(int grade) {

         this.grade = grade;

     }

     public Student(Integer flowId, int type, String idCard, String examCard,

             String studentName, String location, int grade) {

         super();

         this.flowId = flowId;

         this.type = type;

         this.idCard = idCard;

         this.examCard = examCard;

         this.studentName = studentName;

         this.location = location;

         this.grade = grade;

     }

     //用于反射

     public Student() {

     }

     @Override

     public String toString() {

         return "Student [flowId=" + flowId + ", type=" + type + ", idCard="

                 + idCard + ", examCard=" + examCard + ", studentName="

                 + studentName + ", location=" + location + ", grade=" + grade

                 + "]";

     }

 }

5.简单总结

　1）对于MVC设计模式的认识

　　① M: Model. Dao

　　② V: View. JSP, 在页面上填写 Java 代码实现显示

　　③ C: Controller. Serlvet:

　　　　　 I. 受理请求

　　　　 II. 获取请求参数

III. 调用 DAO 方法

　　　　 IV. 可能会把 DAO 方法的返回值放入request 中

　　　　　 V. 转发（或重定向）页面

　　2)问题和足

　　问题：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： I. 代码臃肿，结构不清楚。　　　　　　解决方案：使用数据库连接池，DBUtils，JDBCUtils 工具类，DAO 基类；

　　　　 II. 一个请求一个 Serlvet 不好。　　　　解决方案：一个模块使用一个 Serlvet，即多个请求可以使用一个 Servlet；

　　　　　III. 使用不友好。　　　　　　　　　　　解决方案：在页面上加入 jQuery 操作提示，如删除，保存等。