请使用JAVA语言编写以下要求的代码：IO练习：从键盘上输入任意年份和月份，输出该月份的日历，并输出到文件中。

以下是使用Java语言编写的代码，可实现从键盘上输入任意年份和月份，输出该月份的日历，并输出到文件中：

import java.util.Scanner;
import java.io.*;

public class CalendarIO {
    public static void main(String[] args) throws IOException {
        Scanner input = new Scanner(System.in);
        System.out.print("请输入年份：");
        int year = input.nextInt();
        System.out.print("请输入月份：");
        int month = input.nextInt();

        // 计算该月份的天数
        int days = getDays(year, month);

        // 计算该月份的第一天是星期几
        int firstDayOfWeek = getFirstDayOfWeek(year, month);

        // 输出日历并写入文件
        String calendar = getCalendar(year, month, days, firstDayOfWeek);
        System.out.println(calendar);

        File file = new File("calendar.txt");
        FileWriter writer = new FileWriter(file);
        writer.write(calendar);
        writer.close();
    }

    /**
     * 计算指定年份和月份的天数
     */
    public static int getDays(int year, int month) {
        int days = 0;
        if (month == 2) {
            if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
                days = 29;
            } else {
                days = 28;
            }
        } else if (month == 4 || month == 6 || month == 9 || month == 11) {
            days = 30;
        } else {
            days = 31;
        }
        return days;
    }

    /**
     * 计算指定年份和月份的第一天是星期几
     */
    public static int getFirstDayOfWeek(int year, int month) {
        int days = 0;
        for (int i = 1900; i < year; i++) {
            if (i % 4 == 0 && i % 100 != 0 || i % 400 == 0) {
                days += 366;
            } else {
                days += 365;
            }
        }
        for (int i = 1; i < month; i++) {
            days += getDays(year, i);
        }
        int dayOfWeek = (days + 1) % 7;
        return dayOfWeek;
    }

    /**
     * 获取指定年份和月份的日历
     */
    public static String getCalendar(int year, int month, int days, int firstDayOfWeek) {
        StringBuilder builder = new StringBuilder();

        // 输出年份和月份
        String monthName = getMonthName(month);
        builder.append("\t\t" + year + "年" + monthName + "月\n");

        // 输出星期几
        builder.append("日\t一\t二\t三\t四\t五\t六\n");

        // 输出第一行日期
        for (int i = 0; i < firstDayOfWeek; i++) {
            builder.append("\t");
        }
        for (int i = 1; i <= 7 - firstDayOfWeek; i++) {
            builder.append(i + "\t");
        }
        builder.append("\n");

        // 输出其它行日期
        int count = 7 - firstDayOfWeek + 1;
        while (count <= days) {
            for (int i = 0; i < 7; i++) {
                if (count <= days) {
                    builder.append(count + "\t");
                    count++;
                } else {
                    builder.append("\t");
                }
            }
            builder.append("\n");
        }

        return builder.toString();
    }

    /**
     * 获取月份的名称
     */
    public static String getMonthName(int month) {
        String[] monthNames = {"", "一月", "二月", "三月", "四月", "五月", "六月", "七月", "八月", "九月", "十月", "十一月", "十二月"};
        return monthNames[month];
    }
}

使用说明：

- 在命令行窗口中，输入 `javac CalendarIO.java` 编译程序；
- 输入 `java CalendarIO` 运行程序；
- 按照提示，在命令行窗口中输入任意年份和月份，即可输出该月份的日历，并将其写入文件 `calendar.txt` 中。