Java 实时进度条：在 DOS 面板中显示 MySQL 查询进度

可以通过 Java 程序来实现在 DOS 面板上实时显示 MySQL 查询进度条的功能。下面是一个简单的 Java 程序示例：

import java.sql.*;

public class MySQLQueryProgressBar {

    public static void main(String[] args) {

        String url = 'jdbc:mysql://localhost:3306/testdb';
        String user = 'root';
        String password = 'password';
        String query = 'SELECT * FROM mytable';
        int totalRows = 0;

        try {
            // Connect to MySQL database
            Connection conn = DriverManager.getConnection(url, user, password);
            Statement stmt = conn.createStatement();

            // Get total number of rows in the table
            ResultSet rsCount = stmt.executeQuery('SELECT COUNT(*) FROM mytable');
            if (rsCount.next()) {
                totalRows = rsCount.getInt(1);
            }
            rsCount.close();

            // Execute the query and display progress bar
            ResultSet rs = stmt.executeQuery(query);
            int count = 0;
            System.out.println('Query progress:');
            while (rs.next()) {
                count++;
                int progress = (int) ((double) count / totalRows * 100);
                System.out.print('
[' + '#'.repeat(progress / 5) + ' '.repeat(20 - progress / 5) + '] ' + progress + '%');
                // Process the query result
            }
            rs.close();

            // Close MySQL database connection
            stmt.close();
            conn.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

该程序通过 JDBC 连接 MySQL 数据库，执行指定的查询语句，并在 DOS 面板上实时显示查询进度条。其中，使用SELECT COUNT(*)语句获取表中总行数，然后在处理查询结果时计算出当前进度，最后使用\r回车符实现进度条的实时更新。