为什么Navicat里面SQL有结果,但是ResultSet.next()为空

本文深入探讨了一个在数据库操作中常见的问题:在Navicat中SQL查询有效,但在Java程序中调用ResultSet.next()却返回空的情况。通过分析前端与后端交互过程中的参数问题,最终定位到特殊字符导致的数据读取失败,并给出了解决方案。

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今天记录一个超级有鬼的事情:

Navicat里面SQL有结果,但是ResultSet.next()为空

首先来分析一下
(1)在Navicat里面测试SQL有结果,就说明 本身SQL是没有什么问题的,这点是可以肯定自己的。
(2)程序正确执行,PreparedStatement,Connection这些都没有问题,不然就会被catch捕获了。
(3)debug带入之后,发现是ResultSet.next()出现问题,思考下面的问题:

  1. 开始指针位置位于第一行之前,也就是说,第一次调用next()方法后才能开始获取数据。这种做法的好处在于可以方便地配合while进行遍历,而不用担心取不到第一行。
  2. 指针移动到最后一行之后返回false,可以用作循环结束的条件。在两种情况下:遍历到最后一行之后,或者当 ResultSet 中没有元素行数为0时,返回false退出循环。

一切都OK 啊

那为什么ResultSet.next()出现的没有出现结果呢?

看看我自己前端和后端代码:

<div class="article-category shadow">
		<div class="article-category-title">分类导航</div>
		<!--后面直接换成AJAX,比较方便 -->
		<a href="${pageContext.request.contextPath }/ShowArticlesByType?type='forest'">林业</a>
		<a href="${pageContext.request.contextPath }/ShowArticlesByType?type='fish'">渔业</a>
		<a href="${pageContext.request.contextPath }/ShowArticlesByType?type='plants'">种植业</a>
		<a href="${pageContext.request.contextPath }/ShowArticlesByType?type='sheep'">畜牧业</a>
		<div class="clear"></div>
</div>

首先这是一个div块,他的结果展示为:
在这里插入图片描述
应该出现的结果是,点击相对应的导航,会出现各自的数据。
我的SQL:

select artical_id,img,date,title,author,type,look from artical where type=? limit 5

当然,我这里面使用的是放置SQL注入的PreparedStatement。所以有问号,这个不重要

之后我在Navicat里面测试了一下我的SQL,没问题哈,溜溜的

但是之后的结果我傻逼了,什么也没有,说好的5条东西呢?眼睁睁没了,忍不住抠电脑。。

这个时候看看自己进行前后端数据交互时候的参数*

在这里插入图片描述
看我黄色标志的地方,里面的参数是什么鬼!!
之后看看自己之前的代码:
在这里插入图片描述

那两个点点在参数中不能识别,肯定是他们搞的鬼!
修改之后:

你猜怎么着?
成功啦,那五行数据乖乖出现了!

所以总结:

前后端交互的时候,不管传递的是什么东东,都没有双引号


END

good lunck to you

package dao; import model.Vehicle; import model.VehicleType; import java.sql.*; import java.util.ArrayList; import java.util.List; import java.util.logging.Level; import java.util.logging.Logger; import javax.net.ssl.*; import java.security.Security; public class VehicleDAO { public static final Logger logger = Logger.getLogger(VehicleDAO.class.getName()); // 定义SQL语句 private static final String INSERT_VEHICLE_SQL = "INSERT INTO vehicles (plate_number, color, type, arrival_time, departure_time, is_in_parking_lot) VALUES (?, ?, ?, ?, ?, ?)"; private static final String SELECT_VEHICLE_BY_PLATE = "SELECT * FROM vehicles WHERE plate_number = ?"; private static final String SELECT_ALL_VEHICLES = "SELECT * FROM vehicles"; private static final String SELECT_VEHICLES_IN_PARKING_LOT = "SELECT * FROM vehicles WHERE is_in_parking_lot = true"; private static final String UPDATE_VEHICLE = "UPDATE vehicles SET color = ?, type = ?, arrival_time = ?, departure_time = ?, is_in_parking_lot = ? WHERE plate_number = ?"; private static final String DELETE_VEHICLE = "DELETE FROM vehicles WHERE plate_number = ?"; private static final String COUNT_VEHICLES_IN_PARKING_LOT = "SELECT COUNT(*) FROM vehicles WHERE is_in_parking_lot = true"; // 在获取连接前添加以下代码 static { try { // 允许TLS1.0协议(仅作为临时解决方案) Security.setProperty("jdk.tls.client.protocols", "TLSv1.2"); // 配置信任所有证书 TrustManager[] trustAllCerts = new TrustManager[]{ new X509TrustManager() { @Override public java.security.cert.X509Certificate[] getAcceptedIssuers() { return null; } @Override public void checkClientTrusted(java.security.cert.X509Certificate[] certs, String authType) { } @Override public void checkServerTrusted(java.security.cert.X509Certificate[] certs, String authType) { } } }; SSLContext sslContext = SSLContext.getInstance("TLS"); sslContext.init(null, trustAllCerts, new java.security.SecureRandom()); HttpsURLConnection.setDefaultSSLSocketFactory(sslContext.getSocketFactory()); } catch (Exception e) { e.printStackTrace(); } } // 数据库连接URL private final String jdbcURL = "jdbc:sqlserver:// 10.13.74.3:1433;databaseName=parking_system;" + "user=sa;password=123456;encrypt=false;trustServerCertificate=true;enableTLS1.2=true"; // integratedSecurity=true 启用 Windows 身份验证 public VehicleDAO() { // 检查驱动是否可用 try { Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver"); logger.info("SQL Server JDBC驱动加载成功"); } catch (ClassNotFoundException e) { logger.log(Level.SEVERE, "未找到SQL Server JDBC驱动,请确保已添加依赖", e); } } // 获取数据库连接 protected Connection getConnection() { Connection connection = null; try { logger.info("尝试连接到数据库: " + jdbcURL); connection = DriverManager.getConnection(jdbcURL); logger.info("数据库连接成功"); } catch (SQLException e) { logger.log(Level.SEVERE, "数据库连接失败", e); } return connection; } /** * 插入车辆 */ public boolean insertVehicle(Vehicle vehicle) throws SQLException { boolean rowInserted; try (Connection connection = getConnection(); PreparedStatement preparedStatement = connection.prepareStatement(INSERT_VEHICLE_SQL)) { preparedStatement.setString(1, vehicle.getPlateNumber()); preparedStatement.setString(2, vehicle.getColor()); preparedStatement.setString(3, vehicle.getType().getDescription()); preparedStatement.setTimestamp(4, Timestamp.valueOf(vehicle.getArrivalTime())); if (vehicle.getDepartureTime() != null) { preparedStatement.setTimestamp(5, Timestamp.valueOf(vehicle.getDepartureTime())); } else { preparedStatement.setNull(5, Types.TIMESTAMP); } preparedStatement.setBoolean(6, vehicle.isInParkingLot()); rowInserted = preparedStatement.executeUpdate() > 0; } return rowInserted; } /** * 根据车牌号查询车辆 */ public Vehicle selectVehicle(String plateNumber) throws SQLException { Vehicle vehicle = null; try (Connection connection = getConnection(); PreparedStatement preparedStatement = connection.prepareStatement(SELECT_VEHICLE_BY_PLATE)) { preparedStatement.setString(1, plateNumber); ResultSet rs = preparedStatement.executeQuery(); while (rs.next()) { String color = rs.getString("color"); String typeDesc = rs.getString("type"); Timestamp arrivalTime = rs.getTimestamp("arrival_time"); Timestamp departureTime = rs.getTimestamp("departure_time"); boolean isInParkingLot = rs.getBoolean("is_in_parking_lot"); VehicleType type = VehicleType.fromDescription(typeDesc); vehicle = new Vehicle(plateNumber, color, type); vehicle.setArrivalTime(arrivalTime.toLocalDateTime()); if (departureTime != null) { vehicle.setDepartureTime(departureTime.toLocalDateTime()); } vehicle.setInParkingLot(isInParkingLot); } } return vehicle; } /** * 查询所有车辆 */ public List<Vehicle> selectAllVehicles() throws SQLException { List<Vehicle> vehicles = new ArrayList<>(); try (Connection connection = getConnection(); PreparedStatement preparedStatement = connection.prepareStatement(SELECT_ALL_VEHICLES)) { ResultSet rs = preparedStatement.executeQuery(); while (rs.next()) { String plateNumber = rs.getString("plate_number"); String color = rs.getString("color"); String typeDesc = rs.getString("type"); Timestamp arrivalTime = rs.getTimestamp("arrival_time"); Timestamp departureTime = rs.getTimestamp("departure_time"); boolean isInParkingLot = rs.getBoolean("is_in_parking_lot"); VehicleType type = VehicleType.fromDescription(typeDesc); Vehicle vehicle = new Vehicle(plateNumber, color, type); vehicle.setArrivalTime(arrivalTime.toLocalDateTime()); if (departureTime != null) { vehicle.setDepartureTime(departureTime.toLocalDateTime()); } vehicle.setInParkingLot(isInParkingLot); vehicles.add(vehicle); } } return vehicles; } /** * 查询在场车辆 */ public List<Vehicle> selectVehiclesInParkingLot() throws SQLException { List<Vehicle> vehicles = new ArrayList<>(); try (Connection connection = getConnection(); PreparedStatement preparedStatement = connection.prepareStatement(SELECT_VEHICLES_IN_PARKING_LOT)) { ResultSet rs = preparedStatement.executeQuery(); while (rs.next()) { String plateNumber = rs.getString("plate_number"); String color = rs.getString("color"); String typeDesc = rs.getString("type"); Timestamp arrivalTime = rs.getTimestamp("arrival_time"); Timestamp departureTime = rs.getTimestamp("departure_time"); boolean isInParkingLot = rs.getBoolean("is_in_parking_lot"); VehicleType type = VehicleType.fromDescription(typeDesc); Vehicle vehicle = new Vehicle(plateNumber, color, type); vehicle.setArrivalTime(arrivalTime.toLocalDateTime()); if (departureTime != null) { vehicle.setDepartureTime(departureTime.toLocalDateTime()); } vehicle.setInParkingLot(isInParkingLot); vehicles.add(vehicle); } } return vehicles; } /** * 更新车辆信息 */ public boolean updateVehicle(Vehicle vehicle) throws SQLException { boolean rowUpdated; try (Connection connection = getConnection(); PreparedStatement preparedStatement = connection.prepareStatement(UPDATE_VEHICLE)) { preparedStatement.setString(1, vehicle.getColor()); preparedStatement.setString(2, vehicle.getType().getDescription()); preparedStatement.setTimestamp(3, Timestamp.valueOf(vehicle.getArrivalTime())); if (vehicle.getDepartureTime() != null) { preparedStatement.setTimestamp(4, Timestamp.valueOf(vehicle.getDepartureTime())); } else { preparedStatement.setNull(4, Types.TIMESTAMP); } preparedStatement.setBoolean(5, vehicle.isInParkingLot()); preparedStatement.setString(6, vehicle.getPlateNumber()); rowUpdated = preparedStatement.executeUpdate() > 0; } return rowUpdated; } /** * 删除车辆 */ public boolean deleteVehicle(String plateNumber) throws SQLException { boolean rowDeleted; try (Connection connection = getConnection(); PreparedStatement preparedStatement = connection.prepareStatement(DELETE_VEHICLE)) { preparedStatement.setString(1, plateNumber); rowDeleted = preparedStatement.executeUpdate() > 0; } return rowDeleted; } /** * 统计在场车辆数量 */ public int countVehiclesInParkingLot() throws SQLException { int count = 0; try (Connection connection = getConnection(); PreparedStatement preparedStatement = connection.prepareStatement(COUNT_VEHICLES_IN_PARKING_LOT)) { ResultSet rs = preparedStatement.executeQuery(); if (rs.next()) { count = rs.getInt(1); } } return count; } /** * 根据车型查询车辆 */ public List<Vehicle> selectVehiclesByType(VehicleType type) throws SQLException { List<Vehicle> vehicles = new ArrayList<>(); String sql = "SELECT * FROM vehicles WHERE type = ?"; try (Connection connection = getConnection(); PreparedStatement preparedStatement = connection.prepareStatement(sql)) { preparedStatement.setString(1, type.getDescription()); ResultSet rs = preparedStatement.executeQuery(); while (rs.next()) { String plateNumber = rs.getString("plate_number"); String color = rs.getString("color"); Timestamp arrivalTime = rs.getTimestamp("arrival_time"); Timestamp departureTime = rs.getTimestamp("departure_time"); boolean isInParkingLot = rs.getBoolean("is_in_parking_lot"); Vehicle vehicle = new Vehicle(plateNumber, color, type); vehicle.setArrivalTime(arrivalTime.toLocalDateTime()); if (departureTime != null) { vehicle.setDepartureTime(departureTime.toLocalDateTime()); } vehicle.setInParkingLot(isInParkingLot); vehicles.add(vehicle); } } return vehicles; } } 修改代码使其连接navicat数据库并给出完整代码
最新发布
06-16
### 如何通过 Java 连接 Navicat 并进行数据库操作 Navicat 是一种用于管理数据库的强大工具,它支持多种数据库类型并提供直观的图形界面来简化复杂的数据库操作[^1]。然而,在实际开发过程中,通常需要通过编程语言(如 Java)与 Navicat 所连接的数据库交互。 以下是关于如何通过 Java 使用 JDBC 驱动程序连接到由 Navicat 管理的数据库的具体方法: #### 1. 加载合适的 JDBC 驱动程序 不同的数据库需要加载对应的驱动类。例如,对于 MySQL 数据库,可以使用 `com.mysql.cj.jdbc.Driver` 类;而对于 Informix 数据库,则需加载 `com.informix.jdbc.IfxDriver` 类[^3]。 ```java try { Class.forName("com.mysql.cj.jdbc.Driver"); } catch (ClassNotFoundException e) { System.out.println("JDBC Driver not found."); e.printStackTrace(); } ``` #### 2. 建立数据库连接 构建 URL 字符串以指定目标数据库的位置和其他必要的参数。下面展示了一个针对 MySQL 的示例连接字符串[^5]: ```java String url = "jdbc:mysql://localhost:3306/sampledb?useSSL=false&serverTimezone=UTC"; String user = "root"; String password = "your_password"; try (Connection connection = DriverManager.getConnection(url, user, password)) { if (connection != null) { System.out.println("Connected to the database!"); } } catch (SQLException e) { System.out.println("Failed to connect to the database."); e.printStackTrace(); } ``` 注意:上述代码中的 `sampledb`, `root`, 和 `your_password` 应替换为你自己的数据库名称、用户名以及密码。 #### 3. 创建 Statement 或 PreparedStatement 对象执行 SQL 查询 一旦建立了有效的连接,就可以创建一个 `Statement` 或者更安全的 `PreparedStatement` 来发送 SQL 请求给服务器。 ```java String query = "SELECT * FROM users WHERE id = ?"; try (PreparedStatement preparedStatement = connection.prepareStatement(query)) { preparedStatement.setInt(1, 1); // 设置占位符的实际值 ResultSet resultSet = preparedStatement.executeQuery(); while (resultSet.next()) { int userId = resultSet.getInt("id"); String username = resultSet.getString("username"); System.out.printf("User ID: %d, Username: %s%n", userId, username); } } catch (SQLException e) { System.out.println("Error executing query."); e.printStackTrace(); } ``` 此部分展示了如何准备一条带参数的安全查询语句,并处理返回结果集。 --- ### 注意事项 - **确保依赖项已添加**:在项目中引入相应的 JDBC 驱动 JAR 文件是非常重要的。 - **配置文件路径**:如果采用外部配置方式存储敏感信息比如账号密码等,请妥善保护这些资源免受未授权访问。 - **异常捕获机制完善**:生产环境中应加强错误日志记录以便于后续排查问题。
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