import org.apache.cassandra.io.util.DataIntegrityMetadata.ChecksumValidator; //导入依赖的package包/类
/**
 * Sequentially read bytes from the file and write them to the output stream
 *
 * @param reader The file reader to read from
 * @param validator validator to verify data integrity
 * @param start number of bytes to skip transfer, but include for validation.
 * @param length The full length that should be read from {@code reader}
 * @param bytesTransferred Number of bytes already read out of {@code length}
 *
 * @return Number of bytes read
 *
 * @throws java.io.IOException on any I/O error
 */
protected long write(RandomAccessReader reader, ChecksumValidator validator, int start, long length, long bytesTransferred) throws IOException
{
    int toTransfer = (int) Math.min(transferBuffer.length, length - bytesTransferred);
    int minReadable = (int) Math.min(transferBuffer.length, reader.length() - reader.getFilePointer());

    reader.readFully(transferBuffer, 0, minReadable);
    if (validator != null)
        validator.validate(transferBuffer, 0, minReadable);

    limiter.acquire(toTransfer - start);
    compressedOutput.write(transferBuffer, start, (toTransfer - start));

    return toTransfer;
}
 

import org.apache.cassandra.io.util.DataIntegrityMetadata.ChecksumValidator; //导入依赖的package包/类
/**
 * Sequentially read bytes from the file and write them to the output stream
 *
 * @param reader The file reader to read from
 * @param validator validator to verify data integrity
 * @param start number of bytes to skip transfer, but include for validation.
 * @param length The full length that should be transferred
 * @param bytesTransferred Number of bytes remaining to transfer
 *
 * @return Number of bytes transferred
 *
 * @throws java.io.IOException on any I/O error
 */
protected long write(RandomAccessReader reader, ChecksumValidator validator, int start, long length, long bytesTransferred) throws IOException
{
    int toTransfer = (int) Math.min(transferBuffer.length, length - bytesTransferred);
    int minReadable = (int) Math.min(transferBuffer.length, reader.length() - reader.getFilePointer());

    reader.readFully(transferBuffer, 0, minReadable);
    if (validator != null)
        validator.validate(transferBuffer, 0, minReadable);

    limiter.acquire(toTransfer);
    compressedOutput.write(transferBuffer, start, (toTransfer - start));

    return toTransfer;
}