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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:

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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