簡單的學生管理系統（適合新手理解學習）

首先看一下學生管理系統的體系（我這個系統作的比較簡單） 主要應用到了 MVC模式  JDBC  前端用到了 HTML5  CSS   JS等

 後臺數據處理主要分爲：controller層  repository層  和service層  下面將每一層的代碼進行展現->>>

首先在entity包內進行類的建立   這個系統只實現了對 學生的 CRUD（增刪改查） 因此只須要建立一個學生類（Student）：

package com.xcl.entity; public class Student { private Integer id; private String name; private String password; private Double money; public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } public Double getMoney() { return money; } public void setMoney(Double money) { this.money = money; } public Student(Integer id, String name, String password, Double money) { this.id = id; this.name = name; this.password = password; this.money = money; } @Override public String toString() { return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", password='" + password + '\'' +
                ", money=" + money +
                '}'; } }

 學生類寫完以後 因爲這個系統簡單不須要進行業務邏輯處理   因此我選擇去寫 service層 

 首先寫一個接口 在接口中定義 CRUD 的方法：

package com.xcl.service; import com.xcl.entity.Student; import java.util.List; public interface StudentService { public List<Student> findAll(); public void deleteById(Integer id); public void update(Integer id,String name,String password,Double money); public Student findById(Integer id); public void add(String name,String password,Double money); }

 再寫一個接口的實現類  實現接口中的 CRUD 方法：

package com.xcl.service.impl; import com.xcl.entity.Student; import com.xcl.repository.StudentRepository; import com.xcl.repository.impl.StudentRepositoryImpl; import com.xcl.service.StudentService; import java.util.List; public class StudentServiceImpl implements StudentService { private StudentRepository studentRepository = new StudentRepositoryImpl(); @Override public List<Student> findAll() { return studentRepository.findAll(); } @Override public void deleteById(Integer id) { studentRepository.deleteById(id); } @Override public void update(Integer id, String name, String password, Double money) { studentRepository.update(id, name, password, money); } @Override public Student findById(Integer id) { return studentRepository.findById(id); } @Override public void add(String name, String password, Double money) { studentRepository.add(name, password, money); } }

 寫到這裏service層就算是寫完了

下面咱們進行 repository 和數據庫操做方面的代碼編寫   這裏會用到 JDBC 數據庫鏈接  因此提早寫一個 JDBC 鏈接數據庫的工具類：

package com.xcl.Tools; import java.sql.*; public class JDBCTools { public static Connection getConnection(){ Connection connection = null; try { //1.加載驅動
            Class.forName("com.mysql.cj.jdbc.Driver"); //2.獲取鏈接
            String url = "jdbc:mysql://localhost:3306/user?serverTimezone=UTC"; String user = "root"; String password = "root"; connection = DriverManager.getConnection(url,user,password); } catch (ClassNotFoundException e) { e.printStackTrace(); } catch (SQLException e) { e.printStackTrace(); } return connection; } public static void release(Connection connection, Statement statement, ResultSet resultSet){ try { if(connection!=null){ connection.close(); } if(statement!=null){ statement.close(); } if(resultSet!=null){ resultSet.close(); } } catch (SQLException e) { e.printStackTrace(); } } }

 下面是 repository 層代碼的編寫  仍是老樣子  先寫一個接口   接口裏面寫好須要實現的 CRUD 方法：

package com.xcl.repository; import com.xcl.entity.Student; import java.util.List; public interface StudentRepository { public List<Student> findAll(); public void deleteById(Integer id); public void update(Integer id,String name,String password,Double money); public Student findById(Integer id); public void add(String name,String password,Double money); }

再寫一個實現類 實現接口裏面定義的方法：

package com.xcl.repository.impl; import com.xcl.Tools.JDBCTools; import com.xcl.entity.Student; import com.xcl.repository.StudentRepository; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.util.ArrayList; import java.util.List; public class StudentRepositoryImpl implements StudentRepository { /** * 查詢 * * @return
     */ @Override public List<Student> findAll() { Connection connection = null; PreparedStatement statement = null; ResultSet resultSet = null; List<Student> list = new ArrayList<>(); try { connection = JDBCTools.getConnection(); String sql = "select * from stu"; statement = connection.prepareStatement(sql); resultSet = statement.executeQuery(); Student student = null; while (resultSet.next()) { int id = resultSet.getInt(1); String name = resultSet.getString(2); String password = resultSet.getString(3); Double money = resultSet.getDouble(4); student = new Student(id, name, password, money); list.add(student); } } catch (SQLException e) { e.printStackTrace(); } finally { JDBCTools.release(connection, statement, resultSet); } return list; } /** * * 刪除 * * @param id */ @Override public void deleteById(Integer id) { Connection connection = null; PreparedStatement statement = null; try { connection = JDBCTools.getConnection(); String sql = "delete from stu where id = ?"; statement = connection.prepareStatement(sql); statement.setInt(1, id); statement.executeUpdate(); } catch (SQLException e) { e.printStackTrace(); } finally { JDBCTools.release(connection, statement, null); } } /** * * 修改 * * @param id * @param name * @param password * @param money */ @Override public void update(Integer id, String name, String password, Double money) { Connection connection = null; PreparedStatement statement = null; try { connection = JDBCTools.getConnection(); String sql = "update stu set name =?,password=?,money=? where id=?"; statement = connection.prepareStatement(sql); statement.setString(1, name); statement.setString(2, password); statement.setDouble(3, money); statement.setInt(4, id); statement.executeUpdate(); } catch (SQLException e) { e.printStackTrace(); } finally { JDBCTools.release(connection, statement, null); } } /** * @param id * @return
     */ @Override public Student findById(Integer id) { Connection connection = null; PreparedStatement statement = null; ResultSet resultSet = null; Student student = null; try { connection = JDBCTools.getConnection(); String sql = "select * from stu where id=?"; statement = connection.prepareStatement(sql); System.out.println(sql); statement.setInt(1, id); resultSet = statement.executeQuery(); if (resultSet.next()) { id = resultSet.getInt(1); String name = resultSet.getString(2); String password = resultSet.getString(3); Double money = resultSet.getDouble(4); student = new Student(id, name, password, money); } } catch (SQLException e) { e.printStackTrace(); } finally { JDBCTools.release(connection, statement, resultSet); } return student; } /** * 添加 * * * @param name * @param password * @param money */ @Override public void add(String name, String password, Double money) { Connection connection = null; PreparedStatement statement = null; try { connection = JDBCTools.getConnection(); String sql = "insert into stu (name,password,money) values (?,?,?)"; statement = connection.prepareStatement(sql); statement.setString(1, name); statement.setString(2, password); statement.setDouble(3, money); statement.executeUpdate(); } catch (SQLException e) { e.printStackTrace(); } finally { JDBCTools.release(connection, statement, null); } } }

接下來就是要編寫先後端交互的代碼  也就是 controller 層的編寫

package com.xcl.controller; import com.xcl.service.StudentService; import com.xcl.service.impl.StudentServiceImpl; 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; @WebServlet("/student") public class StudentServlet extends HttpServlet { private StudentService studentService = new StudentServiceImpl(); private final static String USERNAME = "admin"; private final static String PASSWORD = "123"; @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doPost(req, resp); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { req.setCharacterEncoding("UTF-8"); String method = req.getParameter("method"); if (method == null) method = "findAll"; switch (method) { case "findAll": req.setAttribute("list", studentService.findAll()); req.getRequestDispatcher("index.jsp").forward(req, resp); break; case "deleteById": String idStr = req.getParameter("id"); Integer id = Integer.parseInt(idStr); studentService.deleteById(id); resp.sendRedirect("/student"); break; case "findById": idStr = req.getParameter("id"); id = Integer.parseInt(idStr); req.setAttribute("student", studentService.findById(id)); req.getRequestDispatcher("update.jsp").forward(req, resp); break; case "add": String name = req.getParameter("name"); String password = req.getParameter("password"); String money1 = req.getParameter("money"); Double money = Double.parseDouble(money1); studentService.add( name, password, money); resp.sendRedirect("/student"); break; case "update": idStr = req.getParameter("id"); id = Integer.parseInt(idStr); name = req.getParameter("name"); password = req.getParameter("password"); money1 = req.getParameter("money"); money = Double.parseDouble(money1); studentService.update(id, name, password, money); resp.sendRedirect("/student"); break; case "login": String username = req.getParameter("username"); password = req.getParameter("password"); if (username.equals(USERNAME) && password.equals(PASSWORD)) { req.getSession().setAttribute("name", username); resp.sendRedirect("/student"); } else { req.getRequestDispatcher("index.html").forward(req, resp); } break; case "logout": req.getSession().invalidate(); req.getRequestDispatcher("index.html").forward(req, resp); break; } } }

 

原文出處：https://www.cnblogs.com/199600xcl/p/11477280.html