JSP(三层架构与MVC模式)

例子：
1.准备数据库
2.BASEDAO
3.用户登录包含两类：会员、管理员
管理员：操作的是Admin类
会员：操作的是User类
4.创建两个表对应的实体类
5.创建对应表格的DAO类

MVC与三层架构
三层架构 MVC(Model、View、Controller)
表示层（servlet、jsp）------->C(servlet)、V（jsp）
业务逻辑层(service)------------>M(service、entity)
数据访问层(DAO)--------------->M(DAO)

1. BaseDAO部分代码:
   private static final String URL="jdbc:mysql://127.0.0.1:3306/cartoondb2018"private static final String URL=“jdbc:mysql://127.0.0.1:3306/cartoondb2018”
   private static final String USER=“root”;
   private static final String PASSWORD=“123456”;
   private static final String DRIVER=“com.mysql.jdbc.Driver”;
   public static final Connection getConnection(){
   try{
   Class.forName(DRIVER);
   }catch{… return null;}
   Connection con =null;
   try{
   con=DriverManager.getConnection(URL,USER,PASSWORD);
   return con;
   }catch{…}
   return null;
   }
   public static void close(Connection con,PreparedStatement pstmt,ResultSet rs){
   try{
   if(rs != null)rs.close();
   if(pstmt != null)pstmt.close();
   if(con != null&& !con.isClosed())con.close();
   }catch{…}
   }

2. Admin.java(实体类):
   private int id;
   private String userName;
   private String trueName;
   ----->空白处右击------>Source------->Generate Getters and Setters

3. AdminDAO(增删改查四个方法，这里只写查询)
   public Admin select (String userName,String userPwd){
   Connection con=BaseDAO.getConnection();
   if(con != null){
   preparedStatement pstmt=null;
   try{
   String sql=“select * from admin where username=? and userpwd=?”;
   pstmt=con.prepareStatement(sql);
   pstmt.setString(1,userName);
   pstmt.setString(2,userPwd);
   rs=pstmt.executeQuery();
   if(rs != null&& rs.next()){
   Admin admin=new Admin();
   admin.setId(rs.getInt(“id”));
   admin.setUserName(rs.getString(“username”));
   admin.setUserPwd(rs.getString(“userpwd”));
   admin.setTrueName(rs.getString(“truename”));
   return admin;
   }
   }catch{…}finally{
   BaseDAO.close(con,pstmt,rs);
   }

}
return null;
}
4. AdminService.java(完成管理员的登陆功能)
private AdminDAO admindao=new AdminDAO();
public boolean login(String userName,String userPwd){
Admin admin=admindao.select(userName,userPwd);
if(admin == null){
return false;
}else{
return true;
}

}