请使用JAVA代码处理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。

好的，以下是处理IO的JAVA代码：

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

public class Calendar {
  public static void main(String[] args) {
    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 = getDaysOfMonth(year, month);

    // 输出该月份的日历
    printCalendar(year, month, days);

    // 输出到文件中
    try {
      FileWriter writer = new FileWriter("calendar.txt");
      writer.write("年份：" + year + " 月份：" + month + "\n");
      writer.write("日 一 二 三 四 五 六\n");
      int dayOfWeek = getDayOfWeek(year, month, 1);
      for (int i = 1; i <= days; i++) {
        if (i == 1) {
          for (int j = 1; j <= dayOfWeek; j++) {
            writer.write("   ");
          }
        }
        writer.write(String.format("%2d ", i));
        if ((dayOfWeek + i) % 7 == 0) {
          writer.write("\n");
        }
      }
      writer.close();
      System.out.println("日历已输出到文件calendar.txt中。");
    } catch (IOException e) {
      e.printStackTrace();
    }
  }

  /**
   * 获取指定年份月份的天数
   */
  public static int getDaysOfMonth(int year, int month) {
    int days = 0;
    switch (month) {
      case 1:
      case 3:
      case 5:
      case 7:
      case 8:
      case 10:
      case 12:
        days = 31;
        break;
      case 4:
      case 6:
      case 9:
      case 11:
        days = 30;
        break;
      case 2:
        if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)) {
          days = 29;
        } else {
          days = 28;
        }
        break;
    }
    return days;
  }

  /**
   * 获取指定日期是星期几
   */
  public static int getDayOfWeek(int year, int month, int day) {
    if (month == 1 || month == 2) {
      month += 12;
      year--;
    }
    int c = year / 100;
    int y = year % 100;
    int m = month;
    int d = day;
    int w = (y + y / 4 + c / 4 - 2 * c + 26 * (m + 1) / 10 + d - 1) % 7;
    return (w + 7) % 7;
  }

  /**
   * 输出指定年份月份的日历
   */
  public static void printCalendar(int year, int month, int days) {
    System.out.printf("%d年%d月\n", year, month);
    System.out.println("日 一 二 三 四 五 六");
    int dayOfWeek = getDayOfWeek(year, month, 1);
    for (int i = 1; i <= days; i++) {
      if (i == 1) {
        for (int j = 1; j <= dayOfWeek; j++) {
          System.out.print("   ");
        }
      }
      System.out.printf("%2d ", i);
      if ((dayOfWeek + i) % 7 == 0) {
        System.out.println();
      }
    }
    System.out.println();
  }
}

使用以上代码，会将日历输出到控制台，并且将日历输出到文件calendar.txt中。