1.Bean层（Model层）​

1. 角色：就像餐厅里的“菜品”。
2. ​功能：是纯数据对象（如Person类），封装属性和 getter/setter（例如用户名、密码）。
3. ​示例：Person类

package com.bean;public class Person {private int id;private String name;private String pwd;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 String getPwd() {return pwd;}public void setPwd(String pwd) {this.pwd = pwd;}
}

2.Dao层（Data Access Object）​

• 角色：后厨的“厨师”，专注做菜（操作数据）。
• ​功能：直接和数据库对话，执行增删改查（CRUD）。
• ​示例：UserDAO 类中的 saveUser(User user) 方法，负责把用户数据存入数据库。

接口

package com.dao;import com.bean.Person;import java.sql.SQLException;
import java.util.List;public interface PersonDao {public List<Person> queryAll() throws SQLException;public  Boolean selectOne(Person person) throws SQLException;public int save(Person person) throws SQLException;
}

实现接口

package com.dao.impl;import com.bean.Person;
import com.dao.PersonDao;
import com.db.DB;import java.sql.*;
import java.util.ArrayList;
import java.util.List;public class PersonDaoImpl implements PersonDao {// ------------------------- 方法1：查询所有用户 -------------------------@Overridepublic List<Person> queryAll() throws SQLException {Connection connection=new DB().getConnection(); //获取数据库连接Statement statement= connection.createStatement(); //创建SQL执行器ResultSet resultSet= statement.executeQuery("select * from person"); //执行查询SQL语句List list=new ArrayList(); //准备空集合装数据while (resultSet.next()){  //遍历查询结果（一行一行读）Person p=new Person(); //新建数据盒子p.setId(resultSet.getInt(1));  //取第一列（id）放入盒子p.setName(resultSet.getString(2));  //取第二列（name）放入p.setPwd(resultSet.getString(3));  //取第三列（pwd）放入list.add(p); //把盒子加入集合}resultSet.close();statement.close();connection.close();return list;}// ------------------------- 方法2：检查用户名是否存在 -------------------------@Overridepublic Boolean selectOne(Person person) throws SQLException {//Connection connection=new DB().getConnection(); getConnection()为静态方法就可以之间如下:Connection connection= DB.getConnection(); //获取一个数据库连接PreparedStatement statement= connection.prepareStatement("select * from person where name=?");statement.setString(1,person.getName()); //设置参数（替换第一个问号）ResultSet resultSet= statement.executeQuery(); //执行查询if (resultSet.next()){return false;}else {return true;}}// ------------------------- 方法3：保存用户 -------------------------@Overridepublic int save(Person person) throws SQLException {Connection connection= DB.getConnection();//  预编译SQL（提高性能，防止注入）PreparedStatement statement= connection.prepareStatement("insert into person(name,pwd) values(?,?)");statement.setString(1,person.getName()); //设置第一个参数（name）statement.setString(2,person.getPwd()); //设置第二个参数（pwd）int i= statement.executeUpdate(); //执行插入操作statement.close();connection.close();return i; //返回影响的行数（1=成功，0=失败）}
}

3.DB（驱动连接数据库）

• ​角色：餐厅的“仓库”，存储所有食材。
• ​功能：持久化保存数据（如 MySQL、PostgreSQL）

package com.db;import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;public  class  DB {public static Connection getConnection(){Connection connection=null;try {Class.forName("com.mysql.cj.jdbc.Driver");connection= DriverManager.getConnection("jdbc:mysql://localhost:3306/users?serverTimezone=GMT%2B8","root","123456");} catch (ClassNotFoundException e) {e.printStackTrace();} catch (SQLException e) {e.printStackTrace();}return connection;}}

4.Service层

• 角色：餐厅的“经理”，协调复杂流程。
• ​功能：处理业务逻辑（例如注册时检查用户名是否重复 + 加密密码）。
• ​示例：UserService 的 registerUser() 方法会调用 DAO 的多个操作，并处理事务。

接口

package com.service;import com.bean.Person;import java.sql.SQLException;
import java.util.List;public interface PersonSercie {public List<Person> AllPerson() throws SQLException;public boolean register(Person person) throws SQLException;
}

实现接口

package com.service.impl;import com.bean.Person;
import com.dao.PersonDao;
import com.dao.impl.PersonDaoImpl;
import com.service.PersonSercie;import java.sql.SQLException;
import java.util.List;public class PersonServiceImpl implements PersonSercie {@Overridepublic List<Person> AllPerson() throws SQLException {PersonDao dao=new PersonDaoImpl(); // 1. 创建DAO对象，准备访问数据库return dao.queryAll();  // 2. 调用DAO查询所有用户}@Overridepublic boolean register(Person person) throws SQLException {PersonDao dao=new PersonDaoImpl();//检查用户名是否已存在if(dao.selectOne(person)){  //调用DAO查询是否存在同名用户dao.save(person); //无重复 → 保存用户return true; //返回注册成功}else {return false; //返回注册失败}}
}

5.Servlet（Controller层）​

• 角色：餐厅的“服务员”，接待客人并传递需求。
• ​功能：接收 HTTP 请求（如 POST /login），调用 Service 处理，返回响应（跳转页面或 JSON）。
• ​示例：LoginServlet 获取表单参数，交给 UserService 验证登录。

删除

package com.servlet;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 java.io.IOException;
import java.sql.*;@WebServlet(name = "DeleteServlet",urlPatterns = "/del")
public class DeleteServlet extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {String id=request.getParameter("id");try {Class.forName("com.mysql.cj.jdbc.Driver");Connection connection= DriverManager.getConnection("jdbc:mysql://localhost:3306/users?serverTimezone=GMT%2B8","root","123456");//Statement statement= connection.createStatement();PreparedStatement statement= connection.prepareStatement("delete  from person where id=?");statement.setInt(1,Integer.parseInt(id));int i=statement.executeUpdate();if(i>0){response.sendRedirect("listall");}else {response.getWriter().println("Error");}statement.close();connection.close();} catch (ClassNotFoundException e) {e.printStackTrace();} catch (SQLException e) {e.printStackTrace();}}
}

查看

package com.servlet;import com.bean.Person;
import com.service.PersonSercie;
import com.service.impl.PersonServiceImpl;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 java.io.IOException;
import java.sql.*;
import java.util.List;@WebServlet(name = "ListAllServlet",urlPatterns = "/listall")
public class ListAllServlet extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {PersonSercie personSercie=new PersonServiceImpl();try {List<Person> list=personSercie.AllPerson();request.setAttribute("persons",list);request.getRequestDispatcher("listall.jsp").forward(request,response);} catch (SQLException e) {e.printStackTrace();}}
}

增加

package com.servlet;import com.bean.Person;
import com.service.PersonSercie;
import com.service.impl.PersonServiceImpl;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 java.io.IOException;
import java.sql.SQLException;@WebServlet(name = "RegServlet",urlPatterns = "/reg")
public class RegServlet extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {String name=request.getParameter("uname");String pwd=request.getParameter("upwd");Person person=new Person();person.setName(name);person.setPwd(pwd);//调用模型中注册业务逻辑实现PersonSercie personSercie = new PersonServiceImpl(); // 创建服务层对象（业务逻辑处理者）try {if(personSercie.register(person)){  // 调用服务层的注册方法response.sendRedirect("login.jsp");   // 注册成功：跳转到登录页}else {response.sendRedirect("reg.jsp");// 注册失败：返回注册页};} catch (SQLException e) {e.printStackTrace();}}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {}
}

改1

package com.servlet;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 java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;@WebServlet(name = "UpdateDoServlet",urlPatterns = "/updateDo")
public class UpdateDoServlet extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {String id=request.getParameter("id");String name=request.getParameter("username");String pwd=request.getParameter("userpwd");try {Class.forName("com.mysql.cj.jdbc.Driver");Connection connection= DriverManager.getConnection("jdbc:mysql://localhost:3306/users?serverTimezone=GMT%2B8","root","123456");//Statement statement= connection.createStatement();PreparedStatement statement= connection.prepareStatement("update person set name=?,pwd=? where  id=?");statement.setString(1,name);statement.setString(2,pwd);statement.setInt(3,Integer.parseInt(id));int i=statement.executeUpdate();if(i>0){response.sendRedirect("listall");}else {response.getWriter().println("Error");}statement.close();connection.close();} catch (ClassNotFoundException e) {e.printStackTrace();} catch (SQLException e) {e.printStackTrace();}}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {}
}

改2

package com.servlet;import com.bean.Person;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 java.io.IOException;
import java.sql.*;@WebServlet(name = "UpdateServlet",urlPatterns = "/update")
public class UpdateServlet extends HttpServlet {protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {String id=request.getParameter("id");try {Class.forName("com.mysql.cj.jdbc.Driver");Connection connection= DriverManager.getConnection("jdbc:mysql://localhost:3306/users?serverTimezone=GMT%2B8","root","123456");PreparedStatement statement= connection.prepareStatement("select *  from person where id=?");statement.setInt(1,Integer.parseInt(id));ResultSet resultSet=statement.executeQuery();Person p=new Person();if (resultSet.next()){p.setId(resultSet.getInt(1));p.setName(resultSet.getString(2));p.setPwd(resultSet.getString(3));}request.setAttribute("user",p);resultSet.close();statement.close();connection.close();request.getRequestDispatcher("update.jsp").forward(request,response);} catch (ClassNotFoundException e) {e.printStackTrace();} catch (SQLException e) {e.printStackTrace();}}
}

总结

大概流程：就像网购流程：JSP→ 你下单（Servlet收件）→ 调度中心检查（Service处理）→ 仓库存取（DAO操作→仓库DB）→ 最终收到包裹（响应结果）

1. ​用户填写表单
   👉 在 reg.jsp 页面输入用户名和密码，点击提交。

2. ​Servlet接收请求
   👉 RegServlet 像快递员一样收到包裹（HTTP请求），拆开包裹取出数据（request.getParameter）。

3. ​封装成Bean
   👉 把数据装进 Person 盒子（person.setName(name)）。

4. ​Service处理业务
   👉 调度员（PersonServiceImpl）开始工作：

   • 问仓库管理员（DAO）：“这个用户名有人用吗？”（selectOne）
   • 如果没人用，告诉管理员：“存进仓库！”（save）

5. ​DAO操作数据库
   👉 管理员打开仓库（DB连接），执行 SQL 存入数据。

6. ​返回结果给用户
   👉 Servlet 根据结果，跳转到登录页（成功）或返回注册页（失败）。

至于Servlet中doGet和doPost方法该使用哪个