Method CopyPartially

service/hdfsreader/src/main/java/Reader.java:133–183

(String pathStr, OutputStream out, long offset, int length)

    }

    public static void CopyPartially(String pathStr, OutputStream out, long offset, int length) throws IOException {
        logger.info("CopyPartially begin, path: {}, offset: {}, length: {}", new Object[] {pathStr, offset, length});
        Configuration conf = new Configuration();
        Path path = new Path(pathStr);

        try(FileSystem fs = FileSystem.get(path.toUri(), conf)) {
            logger.debug("begin exists, path: {}", pathStr);
            if (!fs.exists(path)) {
                logger.warn("CopyPartially File does not exist, path: {}", pathStr);
                out.write(("File does not exist: " + pathStr).getBytes());
                return;
            }
            logger.debug("begin getFileStatus, path: {}", pathStr);
            FileStatus stat = fs.getFileStatus(path);
            if (stat.isDir()) {
                logger.warn("CopyPartially Can not read directory, path: {}", pathStr);
                out.write(("Can not read directory: " + pathStr).getBytes());
                return;
            }
            if (offset + length > stat.getLen()) {
                logger.warn("CopyPartially Not enough data, path: {}", pathStr);
                out.write(("Not enough data: " + pathStr).getBytes());
                return;
            }

            logger.debug("begin read, path: {}", pathStr);
            try(FSDataInputStream in = fs.open(path)) {
                int bufferSize = 48 * 1024;
                byte[] buffer = new byte[bufferSize];
                int readSize = 0;
                for (long pos = offset; pos < offset + length; pos += readSize) {
                    if (offset + length - pos < bufferSize) {
                        bufferSize = (int)(offset + length - pos);
                    }
                    long begin = System.currentTimeMillis();
                    readSize = in.read(pos, buffer, 0, bufferSize);
                    logger.debug("CopyPartially read time cost: {}, bufferSize: {}",
                        System.currentTimeMillis() - begin, bufferSize);
                    if (readSize == -1) {
                        logger.warn("CopyPartially EOF path: {}, pos: {}, totalLength: {}",
                                    new Object[] {path, pos, stat.getLen()});
                        return;
                    }
                    if (readSize != bufferSize) {
                        logger.warn("CopyPartially readSize: {}, bufferSize: {}", readSize, bufferSize);
                    }
                    out.write(buffer, 0, readSize);
                }
            }
        }
    }
}