Java Servlet数据库操作示例：基于Simple4J封装增删改查

private DB getDB() {
    // 注意：生产环境中建议将敏感信息移至配置文件而非硬编码
    DB.URI = "jdbc:mysql://localhost:3306/forjava"; 
    // DB.DRIVER = "com.mysql.jdbc.Driver"; 
    // DB.USER = "root";
    // DB.PWD = "";
    
    DB.connect("utf-8");   // 建立连接并设置字符集
    return DB.init("users"); // 指定默认操作表名为users
}

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {
    String action = req.getParameter("action");
    if ("show".equalsIgnoreCase(action)) {
        this.findAll(req, resp);
    } else if ("del".equalsIgnoreCase(action)) {
        this.del(req, resp);
    } else if ("edit".equalsIgnoreCase(action)) {
        this.find(req, resp);
    } else if ("update".equalsIgnoreCase(action)) {
        this.update(req, resp);
    } else if ("insert".equalsIgnoreCase(action)) {
        this.insert(req, resp);
    }
}

@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {
    this.doGet(req, resp); // POST请求也转发到GET处理逻辑
}

private void findAll(final HttpServletRequest req, HttpServletResponse resp) {
    DB db = this.getDB();
    // 使用回调处理查询结果
    db.findAll(new DB.QueryAllCallback() {
        public void callback(List<Map<String, Object>> list) {
            req.setAttribute("userList", list); // 将结果存入Request域
        }
    }, "*"); // "*" 表示查询所有列

    try {
        req.getRequestDispatcher("/index.jsp").forward(req, resp);
    } catch (ServletException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

private void find(final HttpServletRequest req, HttpServletResponse resp) {
    DB db = this.getDB();
    String id = req.getParameter("id");
    
    db.find(new DB.QueryCallback() {
        public void callback(Map<String, Object> map) {
            req.setAttribute("user", map);
        }
    }, "id","name","birthday"); // 指定返回的列名

    db.close();
    try {
        req.getRequestDispatcher("/edit.jsp").forward(req, resp);
    } catch (ServletException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

private void del(HttpServletRequest req, HttpServletResponse resp) {
    DB db = this.getDB();
    // 设置删除条件：id = 传入的参数
    db.where(new ContentValues().put("id", req.getParameter("id"))).del();
    db.close();
    // 删除后重新刷新列表
    this.findAll(req, resp);
}

private void update(HttpServletRequest req, HttpServletResponse resp) {
    DB db = this.getDB();
    String id = req.getParameter("id");
    
    // 构建要更新的字段值
    ContentValues values = new ContentValues();
    values.put("name", req.getParameter("user"));
    values.put("pwd", Utils.md5(req.getParameter("pwd"))); // 密码加密处理
    values.put("birthday", req.getParameter("birth"));
    
    // 执行更新：WHERE id=? SET name=?, pwd=?, birthday=?
    db.where(new ContentValues().put("id", id)).update(values);
    db.close();
    this.findAll(req, resp);
}

private void insert(HttpServletRequest req, HttpServletResponse resp) {
    DB db = this.getDB();
    // 提取参数：忽略索引为null的值，从'user'开始截取部分参数
    // 具体行为取决于Utils.params2Array的实现细节
    db.insert(Utils.params2Array(req, 3, "null","user","birth","pwd"));
    db.close();
    this.findAll(req, resp);
}