如何使用JDBC连接数据库并执行SQL语句
作者:互联小助手
JDBC是Java数据库连接的缩写,是Java程序与数据库进行交互的标准API。JDBC主要包括Java.sql和javax.sql两个包,通过DriverManager获取数据库连接对象Connection,并通过Statement或PreparedStatement执行SQL语句
1. JDBC入门
JDBC(Java Database Connectivity)是Java程序与数据库进行交互的一种标准接口,它提供了一种简单的方式来连接和操作数据库。在使用JDBC之前,需要先了解以下几个概念:
- JDBC Driver:JDBC驱动程序是一个Java类,用于将Java应用程序与特定数据库管理系统(DBMS)连接。JDBC驱动程序分为四种类型:JDBC-ODBC桥接驱动程序、本地API驱动程序、网络协议驱动程序和本地协议驱动程序。
- Connection:Connection是一个JDBC接口,用于连接到数据库。在Java程序中,通过Connection接口的实现类来实现与数据库的连接。
- Statement:Statement是一个JDBC接口,用于向数据库发送SQL语句并执行它们。在Java程序中,通过Connection对象创建Statement对象。
- ResultSet:ResultSet是一个JDBC接口,用于表示从数据库中检索到的结果集。ResultSet对象通过Statement对象的executeQuery()方法返回。
下面是一个简单的JDBC连接示例:
import java.sql.*; public class JDBCDemo { public static void main(String[] args) { try { // 加载JDBC驱动程序 Class.forName("com.mysql.cj.jdbc.Driver"); // 建立数据库连接 Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydb", "root", "password"); // 执行SQL查询 Statement stmt = conn.createStatement(); ResultSet rs = stmt.executeQuery("SELECT * FROM users"); while (rs.next()) { System.out.println(rs.getInt(1) + ", " + rs.getString(2) + ", " + rs.getString(3)); } // 关闭数据库连接 rs.close(); stmt.close(); conn.close(); } catch (Exception e) { e.printStackTrace(); } } }
2. 抽取工具类
在实际开发中,我们通常会抽取出一个JDBC工具类来封装JDBC相关操作,以方便代码的重用和维护。下面是一个简单的JDBC工具类示例:
import java.sql.*; public class JDBCUtils { private static final String URL = "jdbc:mysql://localhost:3306/mydb"; private static final String USER = "root"; private static final String PASSWORD = "password"; static { try { // 加载JDBC驱动程序 Class.forName("com.mysql.cj.jdbc.Driver"); } catch (ClassNotFoundException e) { e.printStackTrace(); } } public static Connection getConnection() { Connection conn = null; try { // 建立数据库连接 conn = DriverManager.getConnection(URL, USER, PASSWORD); } catch (SQLException e) { e.printStackTrace(); } return conn; } public static void release(ResultSet rs, Statement stmt, Connection conn) { try { if (rs != null) rs.close(); if (stmt != null) stmt.close(); if (conn != null) conn.close(); } catch (SQLException e) { e.printStackTrace(); } } }
3. Statement CRUD
Statement是JDBC中最基本的操作方式,它用于向数据库发送SQL语句并执行它们。下面是一个使用Statement进行CRUD操作的示例:
import java.sql.*; public class StatementCRUD { public static void main(String[] args) { Connection conn = null; Statement stmt = null; ResultSet rs = null; try { conn = JDBCUtils.getConnection(); stmt = conn.createStatement(); // 插入数据 String sql = "INSERT INTO users (name, age) VALUES ('Tom', 18)"; stmt.executeUpdate(sql); // 更新数据 sql = "UPDATE users SET age = 20 WHERE name = 'Tom'"; stmt.executeUpdate(sql); // 删除数据 sql = "DELETE FROM users WHERE age = 20"; stmt.executeUpdate(sql); // 查询数据 sql = "SELECT * FROM users"; rs = stmt.executeQuery(sql); while (rs.next()) { System.out.println(rs.getInt(1) + ", " + rs.getString(2) + ", " + rs.getInt(3)); } } catch (SQLException e) { e.printStackTrace(); } finally { JDBCUtils.release(rs, stmt, conn); } } }
4. 演练CRUD
下面是一个使用PreparedStatement进行CRUD操作的示例:
import java.sql.*; public class PreparedStatementCRUD { public static void main(String[] args) { Connection conn = null; PreparedStatement pstmt = null; ResultSet rs = null; try { conn = JDBCUtils.getConnection(); // 插入数据 String sql = "INSERT INTO users (name, age) VALUES (?, ?)"; pstmt = conn.prepareStatement(sql); pstmt.setString(1, "Tom"); pstmt.setInt(2, 18); pstmt.executeUpdate(); // 更新数据 sql = "UPDATE users SET age = ? WHERE name = ?"; pstmt = conn.prepareStatement(sql); pstmt.setInt(1, 20); pstmt.setString(2, "Tom"); pstmt.executeUpdate(); // 删除数据 sql = "DELETE FROM users WHERE age = ?"; pstmt = conn.prepareStatement(sql); pstmt.setInt(1, 20); pstmt.executeUpdate(); // 查询数据 sql = "SELECT * FROM users"; pstmt = conn.prepareStatement(sql); rs = pstmt.executeQuery(); while (rs.next()) { System.out.println(rs.getInt(1) + ", " + rs.getString(2) + ", " + rs.getInt(3)); } } catch (SQLException e) { e.printStackTrace(); } finally { JDBCUtils.release(rs, pstmt, conn); } } }
5. Dao模式(声明与实现分开)
Dao(Data Access Object)模式是一种用于封装数据访问逻辑的设计模式。它将数据访问逻辑与业务逻辑分离开来,使得代码更易于维护和扩展。下面是一个使用Dao模式进行CRUD操作的示例:
import java.sql.*; public class UserDAO { private static final String INSERT_SQL = "INSERT INTO users (name, age) VALUES (?, ?)"; private static final String UPDATE_SQL = "UPDATE users SET age = ? WHERE name = ?"; private static final String DELETE_SQL = "DELETE FROM users WHERE age = ?"; private static final String SELECT_SQL = "SELECT * FROM users"; public void insert(User user) { Connection conn = null; PreparedStatement pstmt = null; try { conn = JDBCUtils.getConnection(); pstmt = conn.prepareStatement(INSERT_SQL); pstmt.setString(1, user.getName()); pstmt.setInt(2, user.getAge()); pstmt.executeUpdate(); } catch (SQLException e) { e.printStackTrace(); } finally { JDBCUtils.release(null, pstmt, conn); } } public void update(User user) { Connection conn = null; PreparedStatement pstmt = null; try { conn = JDBCUtils.getConnection(); pstmt = conn.prepareStatement(UPDATE_SQL); pstmt.setInt(1, user.getAge()); pstmt.setString(2, user.getName()); pstmt.executeUpdate(); } catch (SQLException e) { e.printStackTrace(); } finally { JDBCUtils.release(null, pstmt, conn); } } public void delete(int age) { Connection conn = null; PreparedStatement pstmt = null; try { conn = JDBCUtils.getConnection(); pstmt = conn.prepareStatement(DELETE_SQL); pstmt.setInt(1, age); pstmt.executeUpdate(); } catch (SQLException e) { e.printStackTrace(); } finally { JDBCUtils.release(null, pstmt, conn); } } public List<User> selectAll() { Connection conn = null; PreparedStatement pstmt = null; ResultSet rs = null; List<User> userList = new ArrayList<>(); try { conn = JDBCUtils.getConnection(); pstmt = conn.prepareStatement(SELECT_SQL); rs = pstmt.executeQuery(); while (rs.next()) { User user = new User(); user.setId(rs.getInt(1)); user.setName(rs.getString(2)); user.setAge(rs.getInt(3)); userList.add(user); } } catch (SQLException e) { e.printStackTrace(); } finally { JDBCUtils.release(rs, pstmt, conn); } return userList; } } public class User { private int id; private String name; private int age; // 省略getter、setter方法 }
6. PrepareStatement CRUD
PreparedStatement是一种预编译的Statement,它可以通过占位符的方式来替换SQL语句中的参数,避免了SQL注入的危险。下面是一个使用PreparedStatement进行CRUD操作的示例:
import java.sql.*; public class PrepareStatementCRUD { public static void main(String[] args) { Connection conn = null; PreparedStatement pstmt = null; ResultSet rs = null; try { conn = JDBCUtils.getConnection(); // 插入数据 String sql = "INSERT INTO users (name, age) VALUES (?, ?)"; pstmt = conn.prepareStatement(sql); pstmt.setString(1, "Tom"); pstmt.setInt(2, 18); pstmt.executeUpdate(); // 更新数据 sql = "UPDATE users SET age = ? WHERE name = ?"; pstmt = conn.prepareStatement(sql); pstmt.setInt(1, 20); pstmt.setString(2, "Tom"); pstmt.executeUpdate(); // 删除数据 sql = "DELETE FROM users WHERE age = ?"; pstmt = conn.prepareStatement(sql); pstmt.setInt(1, 20); pstmt.executeUpdate(); // 查询数据 sql = "SELECT * FROM users"; pstmt = conn.prepareStatement(sql); rs = pstmt.executeQuery(); while (rs.next()) { System.out.println(rs.getInt(1) + ", " + rs.getString(2) + ", " + rs.getInt(3)); } } catch (SQLException e) { e.printStackTrace(); } finally { JDBCUtils.release(rs, pstmt, conn); } } }
以上就是关于JDBC入门、抽取工具类、Statement CRUD、演练CRUD、Dao模式(声明与实现分开)、PrepareStatement CRUD的详细介绍和代码示例。通过学习这些内容,可以让我们更好地掌握JDBC的使用和开发技巧,从而更好地应用到实际的项目中。
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