做女装的网站,作文网有哪些,网站设计师职责,响应式英文网站建设在 Java 应用程序中#xff0c;三层架构#xff08;Three-Tier Architecture#xff09;是一种常见的设计模式#xff0c;用于分离应用程序的表示层、业务逻辑层和数据访问层。这种架构有助于提高代码的可维护性、可扩展性和可重用性。以下是详细解释 Java 应用程序中使用 …在 Java 应用程序中三层架构Three-Tier Architecture是一种常见的设计模式用于分离应用程序的表示层、业务逻辑层和数据访问层。这种架构有助于提高代码的可维护性、可扩展性和可重用性。以下是详细解释 Java 应用程序中使用 MySQL 的三层架构
### 一、三层架构简介
1. **表示层Presentation Layer** - 负责与用户交互包括用户界面UI的展示和用户输入的处理。 - 通常包含 JSP、Servlet 或其他前端技术如 Thymeleaf、Angular、React 等。
2. **业务逻辑层Business Logic Layer** - 处理应用程序的业务逻辑执行具体的业务操作。 - 通常包含服务类Service、业务对象BO等。
3. **数据访问层Data Access Layer** - 负责与数据库进行交互执行数据的持久化操作。 - 通常包含数据访问对象DAO类。
### 二、示例应用程序
假设我们有一个简单的应用程序用于管理用户信息包括用户的 id 和 name。以下是使用 MySQL 的三层架构示例。
#### 1. 数据库表
首先创建一个 MySQL 数据库表 users
sql CREATE DATABASE testdb;
USE testdb;
CREATE TABLE users ( id INT AUTO_INCREMENT PRIMARY KEY, name VARCHAR(100) NOT NULL );
#### 2. 数据访问层DAO
定义一个数据访问对象DAO类用于与数据库进行交互。
java 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 UserDAO { private String jdbcURL jdbc:mysql://localhost:3306/testdb; private String jdbcUsername root; private String jdbcPassword yourpassword; private static final String INSERT_USERS_SQL INSERT INTO users (name) VALUES (?);; private static final String SELECT_USER_BY_ID SELECT id, name FROM users WHERE id ?; private static final String SELECT_ALL_USERS SELECT * FROM users; private static final String DELETE_USER_SQL DELETE FROM users WHERE id ?;; private static final String UPDATE_USER_SQL UPDATE users SET name ? WHERE id ?;; protected Connection getConnection() { Connection connection null; try { Class.forName(com.mysql.cj.jdbc.Driver); connection DriverManager.getConnection(jdbcURL, jdbcUsername, jdbcPassword); } catch (SQLException | ClassNotFoundException e) { e.printStackTrace(); } return connection; } public void insertUser(User user) throws SQLException { try (Connection connection getConnection(); PreparedStatement preparedStatement connection.prepareStatement(INSERT_USERS_SQL)) { preparedStatement.setString(1, user.getName()); preparedStatement.executeUpdate(); } catch (SQLException e) { e.printStackTrace(); } } public User selectUser(int id) { User user null; try (Connection connection getConnection(); PreparedStatement preparedStatement connection.prepareStatement(SELECT_USER_BY_ID)) { preparedStatement.setInt(1, id); ResultSet rs preparedStatement.executeQuery(); while (rs.next()) { String name rs.getString(name); user new User(id, name); } } catch (SQLException e) { e.printStackTrace(); } return user; } public ListUser selectAllUsers() { ListUser users new ArrayList(); try (Connection connection getConnection(); PreparedStatement preparedStatement connection.prepareStatement(SELECT_ALL_USERS)) { ResultSet rs preparedStatement.executeQuery(); while (rs.next()) { int id rs.getInt(id); String name rs.getString(name); users.add(new User(id, name)); } } catch (SQLException e) { e.printStackTrace(); } return users; } public boolean deleteUser(int id) throws SQLException { boolean rowDeleted; try (Connection connection getConnection(); PreparedStatement statement connection.prepareStatement(DELETE_USER_SQL)) { statement.setInt(1, id); rowDeleted statement.executeUpdate() 0; } return rowDeleted; } public boolean updateUser(User user) throws SQLException { boolean rowUpdated; try (Connection connection getConnection(); PreparedStatement statement connection.prepareStatement(UPDATE_USER_SQL)) { statement.setString(1, user.getName()); statement.setInt(2, user.getId()); rowUpdated statement.executeUpdate() 0; } return rowUpdated; } }
#### 3. 业务逻辑层Service
定义一个服务类处理应用程序的业务逻辑。
java import java.sql.SQLException; import java.util.List;
public class UserService { private UserDAO userDAO; public UserService() { userDAO new UserDAO(); } public void addUser(User user) { try { userDAO.insertUser(user); } catch (SQLException e) { e.printStackTrace(); } } public User getUser(int id) { return userDAO.selectUser(id); } public ListUser getAllUsers() { return userDAO.selectAllUsers(); } public void updateUser(User user) { try { userDAO.updateUser(user); } catch (SQLException e) { e.printStackTrace(); } } public void deleteUser(int id) { try { userDAO.deleteUser(id); } catch (SQLException e) { e.printStackTrace(); } } }
#### 4. 表示层Servlet
使用 Servlet 处理用户请求和响应。
java import java.io.IOException; import java.util.List; import javax.servlet.RequestDispatcher; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse;
WebServlet(/) public class UserServlet extends HttpServlet { private static final long serialVersionUID 1L; private UserService userService; public void init() { userService new UserService(); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String action request.getServletPath(); try { switch (action) { case /new: showNewForm(request, response); break; case /insert: insertUser(request, response); break; case /delete: deleteUser(request, response); break; case /edit: showEditForm(request, response); break; case /update: updateUser(request, response); break; default: listUser(request, response); break; } } catch (SQLException ex) { throw new ServletException(ex); } } private void listUser(HttpServletRequest request, HttpServletResponse response) throws SQLException, IOException, ServletException { ListUser listUser userService.getAllUsers(); request.setAttribute(listUser, listUser); RequestDispatcher dispatcher request.getRequestDispatcher(user-list.jsp); dispatcher.forward(request, response); } private void showNewForm(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { RequestDispatcher dispatcher request.getRequestDispatcher(user-form.jsp); dispatcher.forward(request, response); } private void showEditForm(HttpServletRequest request, HttpServletResponse response) throws SQLException, ServletException, IOException { int id Integer.parseInt(request.getParameter(id)); User existingUser userService.getUser(id); RequestDispatcher dispatcher request.getRequestDispatcher(user-form.jsp); request.setAttribute(user, existingUser); dispatcher.forward(request, response); } private void insertUser(HttpServletRequest request, HttpServletResponse response) throws SQLException, IOException { String name request.getParameter(name); User newUser new User(name); userService.addUser(newUser); response.sendRedirect(list); } private void updateUser(HttpServletRequest request, HttpServletResponse response) throws SQLException, IOException { int id Integer.parseInt(request.getParameter(id)); String name request.getParameter(name); User user new User(id, name); userService.updateUser(user); response.sendRedirect(list); } private void deleteUser(HttpServletRequest request, HttpServletResponse response) throws SQLException, IOException { int id Integer.parseInt(request.getParameter(id)); userService.deleteUser(id); response.sendRedirect(list); } }
#### 5. 用户实体类User
定义一个用户实体类表示数据库表 users 中的记录。
java public class User { private int id; private String name; public User(int id, String name) { this.id id; this.name name; } public User(String name) { this.name name; } 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; } }
#### 6. JSP 页面
定义两个 JSP 页面一个用于显示用户列表另一个用于用户表单。
**user-list.jsp**
jsp % taglib urihttp://java.sun.com/jsp/jstl/core prefixc % !DOCTYPE html html head meta charsetUTF-8 titleUser List/title /head body h2User List/h2 a hrefnewAdd New User/a table border1 tr thID/th thName/th thActions/th /tr c:forEach varuser items${listUser} tr td${user.id}/td td${user.name}/td td a hrefedit?id${user.id}Edit/a a hrefdelete?id${user.id}Delete/a /td /tr /c:forEach /table /body /html
