/**

      * 分片读取文件块

      *

      * @param path      文件路径

      * @param position  角标

      * @param blockSize 文件块大小

      * @return 文件块内容

      */

     public static byte[] read(String path, long position, int blockSize) throws Exception {

         // ----- 校验文件，当文件不存在时，抛出文件不存在异常

         checkFilePath(path, false);

         // ----- 读取文件

         ByteBuffer block = ByteBuffer.allocate(blockSize);

         try (AsynchronousFileChannel channel = AsynchronousFileChannel.open(Paths.get(path), StandardOpenOption.READ)) {

             Future<Integer> read = channel.read(block, position);

             while (!read.isDone()) {

                 // ----- 睡1毫秒， 不抢占资源

                 Thread.sleep(1L);

             }

         }

         return block.array();

     }

     /**

      * 分片写文件

      *

      * @param path     文件目标位置

      * @param block    文件块内容

      * @param position 角标

      * @throws Exception

      */

     public static void write(String path, byte[] block, long position) throws Exception {

         // ----- 校验文件，当文件不存在时，创建新文件

         checkFilePath(path, true);

         // ----- 写文件

         ByteBuffer buffer = ByteBuffer.wrap(block);

         try (AsynchronousFileChannel channel = AsynchronousFileChannel.open(Paths.get(path), StandardOpenOption.WRITE)) {

             Future<Integer> write = channel.write(buffer, position);

             while (!write.isDone()) {

                 // ----- 睡1毫秒， 不抢占资源

                 Thread.sleep(1L);

             }

         }

     }

     /**

      * 校验文件

      *

      * @param path 文件路径

      * @param flag 当文件不存在时是否创建文件 [true: 创建文件；false: 抛出文件不存在异常]

      * @return

      * @throws Exception

      */

     public static File checkFilePath(String path, boolean flag) throws Exception {

         if (StringUtils.isBlank(path)) {

             throw new RuntimeException("The file path cannot be empty.");

         }

         File file = new File(path);

         if (!file.exists()) {

             if (flag) {

                 // ----- 当文件不存在时，创建新文件

                 if (!file.createNewFile()) {

                     throw new RuntimeException("Failed to create file.");

                 }

             } else {

                 // ----- 抛出文件不存在异常

                 throw new RuntimeException("File does not exist.");

             }

         }

         return file;

     }

     /*** 分片读写文件的每片默认大小： 10M */

     private static final Integer DEFAULT_BLOCK_SIZE = 1024 * 1024 * 10;

     public static void main(String[] args) throws Exception {

         String path = "F:\\compression\\Spring源码深度解析.pdf";

         String toPath = "F:\\compression\\" + System.currentTimeMillis() + ".pdf";

         File file = FileUtil.checkFilePath(path, false);

         long position = 0, length = file.length();

         while (length > DEFAULT_BLOCK_SIZE) {

             // ----- 如果文件大小大于默认分块大小，循环读写文件，每次循环读取一块，直到剩余文件大小小于默认分块大小

             byte[] block = FileUtil.read(path, position, DEFAULT_BLOCK_SIZE);

             FileUtil.write(toPath, block, position);

             position += DEFAULT_BLOCK_SIZE;

             length -= DEFAULT_BLOCK_SIZE;

         }

         if (length > 0) {

             // ----- 如果文件大小小于默认分块大小且大于零，正常读写文件

             byte[] block = FileUtil.read(path, position, (int) length);

             FileUtil.write(toPath, block, position);

         }

     }