产生15个20~9999之间的随机整数，然后利用BufferedWriter类将其写入文件file2.txt中；之后再提取该文件中的数据并将它们以升序排列。(Generate random integers between 15 20~9999 and write them into the file file2.txt using the BufferedWriter class; then extract the data in the file and arrange them in ascending order.)