MVC设计模式-练习一

MVC 模式:

• Model（模型） - 模型就是数据,模型代表了web应用中的核心功能,包括业务逻辑层和数据库访问层
• View（视图） -  视图就是网页, JSP，用来展示模型中的数据.主要是用户看到并与之交互的界面,即Java web应用程序的外观
• Controller（控制器） - 控制器用来把不同的数据，显示在不同的视图上。控制器主要负责交互和将用户输入的数据导入模型.

一.操作

1. 新建数据库和表
2. 导入以下文件到eclipse中的lib里
3. 导入servlet-api.jar到项目中
4. 新建实体类Hero

   package bean;
    
   public class Hero {
    
       public int id;
       public String name;
       public float hp;
       public int damage;
   	public int getId() {
   		return id;
   	}
   	public void setId(int id) {
   		this.id = id;
   	}
   	public String getName() {
   		return name;
   	}
   	public void setName(String name) {
   		this.name = name;
   	}
   	public float getHp() {
   		return hp;
   	}
   	public void setHp(float hp) {
   		this.hp = hp;
   	}
   	public int getDamage() {
   		return damage;
   	}
   	public void setDamage(int damage) {
   		this.damage = damage;
   	}
        
   }
   

5. 创建HeroDAO.java,用于从数据库查询数据

   package dao;
     
   import java.sql.Connection;
   import java.sql.DriverManager;
   import java.sql.PreparedStatement;
   import java.sql.ResultSet;
   import java.sql.SQLException;
   import java.sql.Statement;
   import java.util.ArrayList;
   import java.util.List;
    
   import bean.Hero;
     
   public class HeroDAO {
     
       public HeroDAO() {
           try {
               Class.forName("com.mysql.jdbc.Driver");
           } catch (ClassNotFoundException e) {
               e.printStackTrace();
           }
       }
     
       public Connection getConnection() throws SQLException {
           return DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8", "root",
                   "admin");
       }
     
       public int getTotal() {
           int total = 0;
           try (Connection c = getConnection(); Statement s = c.createStatement();) {
     
               String sql = "select count(*) from hero";
     
               ResultSet rs = s.executeQuery(sql);
               while (rs.next()) {
                   total = rs.getInt(1);
               }
     
               System.out.println("total:" + total);
     
           } catch (SQLException e) {
     
               e.printStackTrace();
           }
           return total;
       }
     
       public void add(Hero hero) {
     
           String sql = "insert into hero values(null,?,?,?)";
           try (Connection c = getConnection(); PreparedStatement ps = c.prepareStatement(sql);) {
     
               ps.setString(1, hero.name);
               ps.setFloat(2, hero.hp);
               ps.setInt(3, hero.damage);
     
               ps.execute();
     
               ResultSet rs = ps.getGeneratedKeys();
               if (rs.next()) {
                   int id = rs.getInt(1);
                   hero.id = id;
               }
           } catch (SQLException e) {
     
               e.printStackTrace();
           }
       }
     
       public void update(Hero hero) {
     
           String sql = "update hero set name= ?, hp = ? , damage = ? where id = ?";
           try (Connection c = getConnection(); PreparedStatement ps = c.prepareStatement(sql);) {
     
               ps.setString(1, hero.name);
               ps.setFloat(2, hero.hp);
               ps.setInt(3, hero.damage);
               ps.setInt(4, hero.id);
     
               ps.execute();
     
           } catch (SQLException e) {
     
               e.printStackTrace();
           }
     
       }
     
       public void delete(int id) {
     
           try (Connection c = getConnection(); Statement s = c.createStatement();) {
     
               String sql = "delete from hero where id = " + id;
     
               s.execute(sql);
     
           } catch (SQLException e) {
     
               e.printStackTrace();
           }
       }
     
       public Hero get(int id) {
           Hero hero = null;
     
           try (Connection c = getConnection(); Statement s = c.createStatement();) {
     
               String sql = "select * from hero where id = " + id;
     
               ResultSet rs = s.executeQuery(sql);
     
               if (rs.next()) {
                   hero = new Hero();
                   String name = rs.getString(2);
                   float hp = rs.getFloat("hp");
                   int damage = rs.getInt(4);
                   hero.name = name;
                   hero.hp = hp;
                   hero.damage = damage;
                   hero.id = id;
               }
     
           } catch (SQLException e) {
     
               e.printStackTrace();
           }
           return hero;
       }
     
       public List list() {
           return list(0, Short.MAX_VALUE);
       }
     
       public List list(int start, int count) {
           List heros = new ArrayList();
     
           String sql = "select * from hero order by id desc limit ?,? ";
     
           try (Connection c = getConnection(); PreparedStatement ps = c.prepareStatement(sql);) {
     
               ps.setInt(1, start);
               ps.setInt(2, count);
     
               ResultSet rs = ps.executeQuery();
     
               while (rs.next()) {
                   Hero hero = new Hero();
                   int id = rs.getInt(1);
                   String name = rs.getString(2);
                   float hp = rs.getFloat("hp");
                   int damage = rs.getInt(4);
                   hero.id = id;
                   hero.name = name;
                   hero.hp = hp;
                   hero.damage = damage;
                   heros.add(hero);
               }
           } catch (SQLException e) {
     
               e.printStackTrace();
           }
           return heros;
       }
     
   }
   

6. 创建listHero.jsp

   <%@ page language="java" contentType="text/html; charset=UTF-8"
   	pageEncoding="UTF-8" import="java.util.*"%>
   
   <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
   
   
   		
   
   	
   
   		
   id
   		
   name
   		
   hp
   		
   damage
   		
   edit
   		
   delete
   	
   	
   
   			
   ${hero.id}
   			
   ${hero.name}
   			
   ${hero.hp}
   			
   ${hero.damage}
   			
   edit
   			
   delete
   		
   	
   
   

7. 新建servlet

   package servlet;
   
   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;
   
   import bean.Hero;
   import dao.HeroDAO;
   
   /**
    * Servlet implementation class HeroListServlet
    */
   @WebServlet("/HeroListServlet")
   public class HeroListServlet extends HttpServlet {
   	protected void service(HttpServletRequest request, HttpServletResponse response)
               throws ServletException, IOException {
       List heros = new HeroDAO().list();
           request.setAttribute("heros", heros);
           request.getRequestDispatcher("listHero.jsp").forward(request, response);
    
       }
   }
   

 按照老师的方法创建servlet,然后运行即可

最后运行成功图如下:

 二.总结

        看着how2j和老师的教程把流程做了一遍,虽然中间没有遇到太大的问题,但是并没有彻底理解清楚其中的每一步,只是对MVC设计模式有了一点印象,但是自己讲不清楚为什么.后面要多看一些教程,然后自己重新做一遍,更好地体会MVC的内涵.