4. 项目1 —— 实现一个简易博客系统

梦里梦外; 2022-11-15 03:39 121阅读 0赞

## 1. 需求分析 ##

本项目需要实现一个简易的博客系统，其中功能包括：  
1）注册新用户  
2）登陆已有用户  
3）显示博客列表，包括文章的作者和文章的内容  
4）点击文章就会跳转到文章详情  
5）发布新博客  
6）删除自己的博客

## 2. 数据库设计 ##

设计当前代码中需要用到数据库的几张表，每张表上都有哪些字段，每个表之间有什么关联关系

1）**提取出需求中的“实体”有哪些**  
【用户】【文章】  
确定了有两张表：User表 和 Article表

2)**确定实体需要的属性**  
用户：【名字，密码】  
文章：【标题，内容】

3）**确定实体和实体之间的关系**  
用户和文章应该是【一对多】的关系，在“多”的表中加上外键  
（需要在user表中加入userId字段，表示身份标识  
在Article表中加入一个userId字段，表示该文章是由哪个用户发的）

drop database if exists blogdemo;
    create database blogdemo;
    
    use blogdemo;
    
    drop table if exists article;
    create table user(
     userId int primary key auto_increment,
        name varchar(50) unique,
        password varchar(50)
    );
    
    drop table if exists article;
    create table article(
        articleId int primary key auto_increment,
        title varchar(255),
        content text,
        userId int ,
        foreign key(userId) references user(userId)
    );

创建完成的数据库如下：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MTM2MTg5_size_16_color_FFFFFF_t_70]

## 3. 开始写代码 ##

**a）创建一个类来管理数据库的连接（JDBC）**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MTM2MTg5_size_16_color_FFFFFF_t_70 1]

package model;
    
    //管理数据库连接
    //1.建立连接
    //2.断开连接
    //JDBC使用DataSourcr来管理连接
    //DBUtil相当于是对DataSource再稍微包装一层
    //因为 DataSource 应该是每个应用程序只应该有一个实例
    //DBUtil本质上就是实现了一个单例模式，管理了一个唯一的DataSource实例
    
    //单例模式的实现，有两种风格
    //1.饿汉模式
    //2.懒汉模式（在这里实现的）_______主要问题：线程不安全
    
    import com.mysql.jdbc.jdbc2.optional.MysqlDataSource;
    
    import javax.sql.DataSource;
    import java.sql.Connection;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    
    public class DBUtil {
        
        private static volatile DataSource dataSource = null;
        private static final String URL = "jdbc:mysql://127.0.0.1:3306/blogdome?characterEncoding=utf-8&useSSL=true";
        private static final String USERNAME = "root";
        private static final String PASSWORD = "09050797";
    
        public static DataSource getDataSource(){
        
            if (dataSource == null) {
        
                synchronized (DBUtil.class) {
        
                    if (dataSource == null){
        
                        dataSource = new MysqlDataSource();
                        //需要给DataSource设置一些属性
                        ((MysqlDataSource)dataSource).setURL(URL);
                        ((MysqlDataSource)dataSource).setUser(USERNAME);
                        ((MysqlDataSource)dataSource).setPassword(PASSWORD);
                    }
                }
            }
            return dataSource;
        }
    
        //通过这个方法来获取连接
        public static Connection getConnection(){
        
            try {
        
                return getDataSource().getConnection();
            } catch (SQLException e) {
        
                e.printStackTrace();
            }
            return null;
        }
    
        //通过这个方法断开连接
        public static void close(Connection connection, PreparedStatement statement,
                                 ResultSet resultSet){
        
            try {
        
                if (resultSet != null){
        
                    resultSet.close();
                }
                if (statement != null){
        
                    statement.close();
                }
                if (connection != null){
        
                    connection.close();
                }
            } catch (SQLException e) {
        
                e.printStackTrace();
            }
        }
    }

**b）创建实体类**  
创建一个user类和article类，这俩类的属性要和数据库结构是相关联的  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MTM2MTg5_size_16_color_FFFFFF_t_70 2]

package model;
    
    public class User {
        
        private int userId;
        private String name;
        private String password;
    
        public int getUserId() {
        
            return userId;
        }
    
        public void setUserId(int userId) {
        
            this.userId = userId;
        }
    
        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;
        }
    
    }

package model;
    
    public class Article {
        
        private int articleId;
        private String title;
        private String content;
        private int userId;
    
        public int getArticleId() {
        
            return articleId;
        }
    
        public void setArticleId(int articleId) {
        
            this.articleId = articleId;
        }
    
        public String getTitle() {
        
            return title;
        }
    
        public void setTitle(String title) {
        
            this.title = title;
        }
    
        public String getContent() {
        
            return content;
        }
    
        public void setContent(String content) {
        
            this.content = content;
        }
    
        public int getUserId() {
        
            return userId;
        }
    
        public void setUserId(int userId) {
        
            this.userId = userId;
        }
    }

**c）实现数据库的增删改查**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MTM2MTg5_size_16_color_FFFFFF_t_70 3]

package model;
    
    import java.sql.Connection;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    
    //Dao表示数据访问层
    public class UserDao {
        
        //1.新增用户（注册）
        //  把一个User对象插入到数据库中
        void add(User user){
        
            //1.获取带数据库连接
            Connection connection = DBUtil.getConnection();
            //2.拼装sql语句
            String sql = "insert into user values (null,?,?)";
            PreparedStatement statement = null;
            try {
        
                statement = connection.prepareStatement(sql);
                statement.setString(1,user.getName());
                statement.setString(2,user.getPassword());
                //3.执行sql语句
                int ret = statement.executeUpdate();
                if(ret != 1){
        
                    //插入失败
                    System.out.println("插入新用户失败！");
                    return;
                }
                System.out.println("插入新用户成功！");
            } catch (SQLException e) {
        
                e.printStackTrace();
            }finally {
        
                //4.释放数据库连接
                DBUtil.close(connection,statement,null);
            }
        }
    
        //2.按照名字查找（登录）
        public User selectByName(String name){
        
            //1.和数据库建立连接
            Connection connection = DBUtil.getConnection();
            //2.拼装SQL
            String sql = "select * from user where name = ?";
            PreparedStatement statement = null;
            ResultSet resultSet = null;
            try {
        
                statement = connection.prepareStatement(sql);
                statement.setString(1,name);
                //3.执行SQL
                resultSet = statement.executeQuery();
                //4.遍历结果集合
                if (resultSet.next()){
        
                    User user = new User();
                    user.setUserId(resultSet.getInt("userId"));
                    user.setName(resultSet.getString("name"));
                    user.setPassword(resultSet.getString("password"));
                    return user;
                }
            } catch (SQLException e) {
        
                e.printStackTrace();
            }finally {
        
                //5.释放数据库连接
                DBUtil.close(connection,statement,resultSet);
            }
            return null;
        }
    }

package model;
    
    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 ArticleDao {
        
        //1.新增文章（发布博客）
        public void add(Article article){
        
            //1.获取数据库连接
            Connection connection = DBUtil.getConnection();
            //2.构造sql
            String sql = "insert into article value (null,?,?,?)";
            PreparedStatement statement = null;
            try {
        
                statement = connection.prepareStatement(sql);
                statement.setString(1,article.getTitle());
                statement.setString(2,article.getContent());
                statement.setInt(3,article.getUserId());
                //3.执行sql
                int ret = statement.executeUpdate();
                if (ret != 1){
        
                    System.out.println("插入文章操作失败！");
                    return;
                }
                System.out.println("插入文章操作成功！");
            } catch (SQLException e) {
        
                e.printStackTrace();
            }finally {
        
                //4.释放连接
                DBUtil.close(connection,statement,null);
            }
        }
    
    
        //2.查看文章（把所有的文章信息都查出来）
        public List<Article> selectAll(){
        
            List<Article> articles = new ArrayList<>();
            Connection connection = DBUtil.getConnection();
            String sql = "select article,title,userId from article";
            PreparedStatement statement = null;
            ResultSet resultSet = null;
            try {
        
                statement = connection.prepareStatement(sql);
                resultSet = statement.executeQuery();
                while (resultSet.next()){
        
                    Article article = new Article();
                    article.setArticleId(resultSet.getInt("articleId"));
                    article.setTitle(resultSet.getString("title"));
                    article.setUserId(resultSet.getInt("userId"));
                    articles.add(article);
                }
                return articles;
            } catch (SQLException e) {
        
                e.printStackTrace();
            }finally {
        
                DBUtil.close(connection,statement,resultSet);
            }
            return null;
        }
    
        //3.查看指定的文章详情
        public Article selectById(int articleId){
        
            Connection connection = DBUtil.getConnection();
            String sql = "select * from where articleId = ?";
            PreparedStatement statement = null;
            ResultSet resultSet = null;
            try {
        
                statement = connection.prepareStatement(sql);
                statement.setInt(1,articleId);
                resultSet = statement.executeQuery();
                if (resultSet.next()){
        
                    Article article = new Article();
                    article.setArticleId(resultSet.getInt("articleId"));
                    article.setTitle(resultSet.getString("title"));
                    article.setContent(resultSet.getString("content"));
                    article.setUserId(resultSet.getInt("userId"));
                    return article;
                }
            } catch (SQLException e) {
        
                e.printStackTrace();
            }finally {
        
                DBUtil.close(connection,statement,resultSet);
            }
            return null;
        }
    
        //4.删除指定文章
        public void delete(int articleId){
        
            Connection connection = DBUtil.getConnection();
            String sql = "delete from article where articleId = ?";
            PreparedStatement statement = null;
            try {
        
                statement = connection.prepareStatement(sql);
                statement.setInt(1,articleId);
                int ret = statement.executeUpdate();
                if (ret != 1){
        
                    System.out.println("删除文章失败！");
                    return;
                }
                System.out.println("删除文章成功！");
            } catch (SQLException e) {
        
                e.printStackTrace();
            }finally {
        
                DBUtil.close(connection,statement,null);
            }
        }
    }

## 4. 前后端接口设计 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MTM2MTg5_size_16_color_FFFFFF_t_70 4]

## 5. 开始实现接口 ##

**1) 实现注册页面**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MTM2MTg5_size_16_color_FFFFFF_t_70 5]

**register.html**

<!doctype html>
    <html lang="en">
    <head>
        <meta charset="UTF-8">
        <meta name="viewport"
              content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
        <meta http-equiv="X-UA-Compatible" content="ie=edge">
        <title>注册</title>
    </head>
    <body>
    <form action="register" method="post">
        <input type="text" name="name" placeholder="请输入密码">
        <br/>
        <input type="text" name="password" placeholder="请输入密码">
        <br/>
        <input type="submit" value="注册">
    
    </form>
    
    </body>
    </html>

**RegisterServlet**

package api;
    
    import model.User;
    import model.UserDao;
    import view.HtmlGenerator;
    
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.IOException;
    
    public class RegisterServlet extends HttpServlet {
        
        //浏览器是通过POST方法来提交数据的
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        
            resp.setContentType("text/html; charset=utf-8");
            //1.获取到前端提交的数据（用户名，密码）校验是否合法
            String name = req.getParameter("name");
            String password = req.getParameter("password");
            if(name == null || "".equals(name)||password==null||"".equals(password)){
        
                String html = HtmlGenerator.getMessagePage("用户名或者密码为空","register.html");
                resp.getWriter().write(html);
                return;
            }
            //2.拿着用户名在数据库中查一下，看看当前用户是否已经存在，如果存在，认为注册失败
            UserDao userDao = new UserDao();
            User existUser = userDao.selectByName(name);
            if (existUser != null){
        
                //说明已经存在，提示用户注册失败，用户名重复
                String html = HtmlGenerator.getMessagePage("用户名重复！请换个名字！","register.html");
                resp.getWriter().write(html);
                return;
            }
            //3.根据前端提交的数据构造user对象，并插入到数据库中
            User user = new User();
            user.setName(name);
            user.setPassword(password);
            userDao.add(user);
            //4.返回一个结果页面，提示当前注册成功
            String html = HtmlGenerator.getMessagePage("注册成功！点击这里跳转到登陆页面！","login.html");
            resp.getWriter().write(html);
            
        }
    }

**HtmlGenerator**

package view;
    
    public class HtmlGenerator {
        
        //通过字符串拼接的形式，构造出来HTML格式出来
        public static String getMessagePage(String message, String nextUrl) {
        
            StringBuilder stringBuilder = new StringBuilder();
            stringBuilder.append("<html>");
            stringBuilder.append("<head>");
            stringBuilder.append("<meta charset=\"utf-8\">");
            stringBuilder.append("<title>提示页面</title>");
            stringBuilder.append("</head>");
            stringBuilder.append("<body>");
    
            stringBuilder.append("<h3>");
            stringBuilder.append(message);
            stringBuilder.append("</h3>");
    
            stringBuilder.append(String.format("<a href=\"%s\"> 点击这里跳转 </a>",nextUrl));
    
            stringBuilder.append("</body>");
            stringBuilder.append("</html>");
    
            return stringBuilder.toString();
    
        }
    }

**配置web.xml文件**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MTM2MTg5_size_16_color_FFFFFF_t_70 6]  
**2) 实现登录功能**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MTM2MTg5_size_16_color_FFFFFF_t_70 7]  
**login.html**

<!doctype html>
    <html lang="en">
    <head>
        <meta charset="UTF-8">
        <meta name="viewport"
              content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
        <meta http-equiv="X-UA-Compatible" content="ie=edge">
        <title>登录</title>
    </head>
    <body>
    <form action="login" method="post">
        <input type="text" name="name" placeholder="请输入用户名">
        <br/>
        <input type="password" name="password" placeholder="请输入密码">
        <br/>
        <input type="submit" value="登录">
    
    </form>
    
    </body>
    </html>

**loginServlet**

package api;
    
    import model.User;
    import model.UserDao;
    import view.HtmlGenerator;
    
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpSession;
    import java.io.IOException;
    
    public class loginServlet extends HttpServlet {
        
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        
            resp.setContentType("text/html; charset=utf-8");
            //1.获取到用户名和密码，并进行简单的校验
            String name = req.getParameter("name");
            String password = req.getParameter("password");
            if (name == null || "".equals(name) || password==null || "".equals(password)){
        
                String html = HtmlGenerator.getMessagePage("用户名或密码为空","login.html");
                resp.getWriter().write(html);
                return;
            }
            //2.数据库中查找，看看用户是否存在
            //3.对比密码是否匹配
            UserDao userDao = new UserDao();
            User user = userDao.selectByName(name);
            if (user==null || !password.equals(user.getPassword())){
        
                //用户名不存在
                String html = HtmlGenerator.getMessagePage("用户名或密码错误","login.html");
                resp.getWriter().write(html);
                return;
            }
    
            //4.匹配成功则认为登陆成功，创建一个session
            HttpSession httpSession = req.getSession(true);
            httpSession.setAttribute("user",user);
    
            //5.返回一个登陆成功的页面
            String html = HtmlGenerator.getMessagePage("登陆成功","article");
            resp.getWriter().write(html);
        }
    }

**3) 实现文章功能**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQ1MTM2MTg5_size_16_color_FFFFFF_t_70 8]  
**ArticleServlet**

package api;
    
    import model.Article;
    import model.ArticleDao;
    import model.User;
    import model.UserDao;
    import view.HtmlGenerator;
    
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpSession;
    import java.io.IOException;
    import java.util.List;
    
    public class ArticleServlet extends HttpServlet {
        
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        
            resp.setContentType("text/html; charset=utf-8");
            //1.验证用户是否已经登陆了，如果尚未登陆提示用户登录
            HttpSession httpSession = req.getSession(false);
            if (httpSession == null){
        
                //当前是未登录状态
                String html = HtmlGenerator.getMessagePage("请先登录","login.html");
                resp.getWriter().write(html);
                return;
            }
            User user = (User)httpSession.getAttribute("user");
            //2.判断请求中是否存在articleId参数
            String articleIdStr = req.getParameter("articleId");
            if (articleIdStr == null){
        
                //a）没有这个参数就去执行获取文章列表的操作
                getAllArticle(user, resp);
            }else {
        
                //b）有这个参数就去执行获取文章详情的操作
                getOneArticle(Integer.parseInt(articleIdStr),user,resp);
            }
    
        }
    
        private void getOneArticle(int articleId, User user, HttpServletResponse resp) throws IOException {
        
            //1.查找数据库
            ArticleDao articleDao = new ArticleDao();
            Article article = articleDao.selectById(articleId);
            if (article == null){
        
                //文章未找到
                String html = HtmlGenerator.getMessagePage("文章不存在","article");
                resp.getWriter().write(html);
                return;
            }
            //根据作者ID。找到作者信息，进一步得到作者姓名
            UserDao userDao = new UserDao();
            User author = userDao.selectById(article.getUserId());
            //2.构造页面
            String html = HtmlGenerator.getArticleDetailPage(article,user,author);
            resp.getWriter().write(html);
        }
    
    
        private void getAllArticle(User user, HttpServletResponse resp) throws IOException {
        
            //1.查找数据库
            ArticleDao articleDao = new ArticleDao();
            List<Article> articles = articleDao.selectAll();
            //2.构造页面
            String html = HtmlGenerator.getArticleListPage(articles, user);
            resp.getWriter().write(html);
        }
    }

**HtmlGenerator**

package view;
    
    import model.Article;
    import model.User;
    
    import java.util.List;
    
    public class HtmlGenerator {
        
        //通过字符串拼接的形式，构造出来HTML格式出来
        public static String getMessagePage(String message, String nextUrl) {
        
            StringBuilder stringBuilder = new StringBuilder();
            stringBuilder.append("<html>");
            stringBuilder.append("<head>");
            stringBuilder.append("<meta charset=\"utf-8\">");
            stringBuilder.append("<title>提示页面</title>");
            stringBuilder.append("</head>");
            stringBuilder.append("<body>");
    
            stringBuilder.append("<h3>");
            stringBuilder.append(message);
            stringBuilder.append("</h3>");
    
            stringBuilder.append(String.format("<a href=\"%s\"> 点击这里跳转 </a>",nextUrl));
    
            stringBuilder.append("</body>");
            stringBuilder.append("</html>");
    
            return stringBuilder.toString();
    
        }
    
        public static String getArticleListPage(List<Article> articles, User user) {
        
            StringBuilder stringBuilder = new StringBuilder();
            stringBuilder.append("<html>");
            stringBuilder.append("<head>");
            stringBuilder.append("<meta charset=\"utf-8\">");
            stringBuilder.append("<title>提示页面</title>");
            stringBuilder.append("<style>");
            stringBuilder.append("a{"+
                    "color: #333;"+
                    "text-decoration: none;"+
                    "}");
            stringBuilder.append("a{"+
                    "color: white"+
                    "background-color: orange;"+
                    "}");
            stringBuilder.append("</style>");
            stringBuilder.append("</head>");
            stringBuilder.append("<body>");
    
            stringBuilder.append("<h3> 欢迎您！"+ user.getName()+"</h3>");
            stringBuilder.append("<hr>");
            //要有一个文章列表，显示每个文章的标题
            for (Article article : articles){
        
               stringBuilder.append(String.format("<div style=\"width: 200px;height: 50px\"><a href=\"article?articleId=%d\"> %s </div>",
               article.getArticleId(),article.getTitle()));
            }
            stringBuilder.append("<hr>");
            stringBuilder.append(String.format("<div>当前共有博客 %d 篇 </div>",articles.size()));
    
            stringBuilder.append("</body>");
            stringBuilder.append("</html>");
    
            return stringBuilder.toString();
        }
    
    
        public static String getArticleDetailPage(Article article, User user, User author) {
        
            StringBuilder stringBuilder = new StringBuilder();
            stringBuilder.append("<html>");
            stringBuilder.append("<head>");
            stringBuilder.append("<meta charset=\"utf-8\">");
            stringBuilder.append("<title>提示页面</title>");
            stringBuilder.append("<style>");
            stringBuilder.append("a{"+
                    "color: #333;"+
                    "text-decoration: none;"+
                    "}");
            stringBuilder.append("a{"+
                    "color: white"+
                    "background-color: orange;"+
                    "}");
            stringBuilder.append("</style>");
            stringBuilder.append("</head>");
            stringBuilder.append("<body>");
    
            stringBuilder.append("<h3> 欢迎您！"+ user.getName()+"</h3>");
            stringBuilder.append("<hr>");
    
            stringBuilder.append(String.format("<h1>%s</h1>",article.getTitle()));
            stringBuilder.append(String.format("<h4>作者：%s</h4>",author.getName()));
            stringBuilder.append(String.format("<div>%s</div>",article.getContent()));
    
            stringBuilder.append("</body>");
            stringBuilder.append("</html>");
            return stringBuilder.toString();
    
        }
    }

**3) 实现删除文章**

package api;
    
    
    import model.Article;
    import model.ArticleDao;
    import model.User;
    import view.HtmlGenerator;
    
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpSession;
    import java.io.IOException;
    
    public class DeleteArticleServlet extends HttpServlet {
        
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        
            resp.setContentType("text/html; charset=utf-8");
            // 1. 验证用户的登陆状态, 如果未登陆, 肯定不能删除.
            HttpSession httpSession = req.getSession(false);
            if (httpSession == null) {
        
                String html = HtmlGenerator.getMessagePage("您尚未登陆!",
                        "login.html");
                resp.getWriter().write(html);
                return;
            }
            User user = (User) httpSession.getAttribute("user");
            // 2. 读取请求内容, 获取到要删除的文章 id
            String articleIdStr = req.getParameter("articleId");
            if (articleIdStr == null || "".equals(articleIdStr)) {
        
                String html = HtmlGenerator.getMessagePage("要删除的文章 id 有误",
                        "article");
                resp.getWriter().write(html);
                return;
            }
            // 3. 根据文章 id 查找到该文章的作者. 当前用户如果就是作者, 才能删除, 否则删除失败.
            ArticleDao articleDao = new ArticleDao();
            Article article = articleDao.selectById(Integer.parseInt(articleIdStr));
            if (article.getUserId() != user.getUserId()) {
        
                String html = HtmlGenerator.getMessagePage("您只能删除自己的文章!",
                        "article");
                resp.getWriter().write(html);
                return;
            }
            // 4. 真正执行数据库删除操作
            articleDao.delete(Integer.parseInt(articleIdStr));
            // 5. 返回一个 "删除成功" 的页面.
            String html = HtmlGenerator.getMessagePage("删除成功!",
                    "article");
            resp.getWriter().write(html);
        }
    }

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