## 6. 数据库访问 ### 6.1 JDBC #### 6.1.3 实现第一个JDBC程序 **练习任务**: 1. **创建数据库表**: - 根据PetClinic中的`Owner`实体模型创建一个表，包含`id`（整数，主键，自增）、`firstName`（字符串，长度255，不可为空）、`lastName`（字符串，长度255，不可为空）、`address`（字符串，长度255）、`city`（字符串，长度255）、`telephone`（字符串，长度255）字段。 - 示例代码: ```java private static void createOwnerTable(Connection conn) throws SQLException { String sql = "CREATE TABLE IF NOT EXISTS owners (" + "id INT AUTO_INCREMENT PRIMARY KEY," + "firstName VARCHAR(255) NOT NULL," + "lastName VARCHAR(255) NOT NULL," + "address VARCHAR(255)," + "city VARCHAR(255)," + "telephone VARCHAR(255))"; try (PreparedStatement stmt = conn.prepareStatement(sql)) { stmt.executeUpdate(); } } ``` 2. **插入业主记录**: - 向`owners`表中插入两条记录。 - 示例代码: ```java private static void insertOwners(Connection conn) throws SQLException { String sql = "INSERT INTO owners (firstName, lastName, address, city, telephone) VALUES (?, ?, ?, ?, ?)"; try (PreparedStatement pstmt = conn.prepareStatement(sql)) { pstmt.setString(1, "Alice"); pstmt.setString(2, "Johnson"); pstmt.setString(3, "123 Main St"); pstmt.setString(4, "Springfield"); pstmt.setString(5, "555-1234"); pstmt.executeUpdate(); pstmt.setString(1, "Bob"); pstmt.setString(2, "Smith"); pstmt.setString(3, "456 Elm St"); pstmt.setString(4, "Springfield"); pstmt.setString(5, "555-5678"); pstmt.executeUpdate(); } } ``` 3. **查询业主记录**: - 查询`owners`表中的所有记录，并打印出每条记录的信息。 - 示例代码: ```java private static void queryOwners(Connection conn) throws SQLException { String sql = "SELECT * FROM owners"; try (PreparedStatement pstmt = conn.prepareStatement(sql); ResultSet rs = pstmt.executeQuery()) { while (rs.next()) { int id = rs.getInt("id"); String firstName = rs.getString("firstName"); String lastName = rs.getString("lastName"); String address = rs.getString("address"); String city = rs.getString("city"); String telephone = rs.getString("telephone"); System.out.println("ID: " + id + ", First Name: " + firstName + ", Last Name: " + lastName + ", Address: " + address + ", City: " + city + ", Telephone: " + telephone); } } } ``` 4. **更新业主记录**: - 更新`owners`表中名字为"Alice Johnson"的业主的电话号码为"555-1111"。 - 示例代码: ```java private static void updateOwner(Connection conn) throws SQLException { String sql = "UPDATE owners SET telephone = ? WHERE firstName = ? AND lastName = ?"; try (PreparedStatement pstmt = conn.prepareStatement(sql)) { pstmt.setString(1, "555-1111"); pstmt.setString(2, "Alice"); pstmt.setString(3, "Johnson"); int rowsUpdated = pstmt.executeUpdate(); System.out.println(rowsUpdated + " row(s) updated."); } } ``` 5. **删除业主记录**: - 删除`owners`表中名字为"Bob Smith"的业主记录。 - 示例代码: ```java private static void deleteOwner(Connection conn) throws SQLException { String sql = "DELETE FROM owners WHERE firstName = ? AND lastName = ?"; try (PreparedStatement pstmt = conn.prepareStatement(sql)) { pstmt.setString(1, "Bob"); pstmt.setString(2, "Smith"); int rowsDeleted = pstmt.executeUpdate(); System.out.println(rowsDeleted + " row(s) deleted."); } } ``` 6. **完整程序**: - 将以上步骤整合到一个完整的程序中，确保正确加载MySQL驱动、建立数据库连接，并处理异常。 - 示例代码: ```java import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; public class JdbcCrudExample { private static final String DB_URL = "jdbc:mysql://localhost:3306/petclinic"; private static final String USER = "root"; private static final String PASS = "password"; public static void main(String[] args) { Connection conn = null; try { // 加载MySQL驱动 Class.forName("com.mysql.cj.jdbc.Driver"); // 获取数据库连接 conn = DriverManager.getConnection(DB_URL, USER, PASS); // 创建表 createOwnerTable(conn); // 插入记录 insertOwners(conn); // 查询记录 queryOwners(conn); // 更新记录 updateOwner(conn); // 删除记录 deleteOwner(conn); // 再次查询记录 queryOwners(conn); } catch (ClassNotFoundException | SQLException e) { e.printStackTrace(); } finally { if (conn != null) { try { conn.close(); } catch (SQLException e) { e.printStackTrace(); } } } } // 其他方法... } ``` ### 6.3 SQL注入的预防措施 **练习任务**: 1. **使用PreparedStatement防止SQL注入**: - 修改上述的`queryOwners`方法，使用`PreparedStatement`来执行查询。 - 示例代码: ```java private static void queryOwners(Connection conn) throws SQLException { String sql = "SELECT * FROM owners WHERE firstName = ? AND lastName = ?"; try (PreparedStatement pstmt = conn.prepareStatement(sql)) { pstmt.setString(1, "Alice"); pstmt.setString(2, "Johnson"); ResultSet rs = pstmt.executeQuery(); while (rs.next()) { int id = rs.getInt("id"); String firstName = rs.getString("firstName"); String lastName = rs.getString("lastName"); String address = rs.getString("address"); String city = rs.getString("city"); String telephone = rs.getString("telephone"); System.out.println("ID: " + id + ", First Name: " + firstName + ", Last Name: " + lastName + ", Address: " + address + ", City: " + city + ", Telephone: " + telephone); } } } ``` ### 6.2 数据库连接池 #### 6.2.4 使用HikariCP实现数据库连接池 **练习任务**: 1. **配置HikariCP连接池**: - 使用HikariCP配置一个连接池，并使用它来获取数据库连接。 - 示例代码: ```java import com.zaxxer.hikari.HikariConfig; import com.zaxxer.hikari.HikariDataSource; import java.sql.Connection; import java.sql.SQLException; public class HikariCpExample { public static void main(String[] args) { HikariConfig config = new HikariConfig(); config.setJdbcUrl("jdbc:mysql://localhost:3306/petclinic"); config.setUsername("root"); config.setPassword("password"); config.setMaximumPoolSize(10); config.setConnectionTimeout(30000); HikariDataSource ds = new HikariDataSource(config); try (Connection conn = ds.getConnection()) { // 使用连接执行数据库操作 System.out.println("Database connection established."); } catch (SQLException e) { e.printStackTrace(); } } } ```