Interface ReadableChannel

  • All Superinterfaces:
    java.lang.AutoCloseable, java.nio.channels.Channel, java.io.Closeable, java.nio.channels.ReadableByteChannel

    public interface ReadableChannel
    extends java.nio.channels.ReadableByteChannel
    Readable random access byte channel from a file.
    • Method Summary

      All Methods Instance Methods Abstract Methods 
      Modifier and Type Method Description
      int blockSize()
      Get the recommended alignment for reads.
      long position()
      Get the current position of the channel.
      void position​(long newPosition)
      Seek the current position of the channel to a new offset.
      long size()
      Get the total size of the channel.
      • Methods inherited from interface java.nio.channels.Channel

        close, isOpen
      • Methods inherited from interface java.nio.channels.ReadableByteChannel

        read
    • Method Detail

      • position

        long position()
               throws java.io.IOException
        Get the current position of the channel.
        Returns:
        r current offset.
        Throws:
        java.io.IOException - the channel's current position cannot be obtained.
      • position

        void position​(long newPosition)
               throws java.io.IOException
        Seek the current position of the channel to a new offset.
        Parameters:
        newPosition - position to move the channel to. The next read will start from here. This should be a multiple of the blockSize().
        Throws:
        java.io.IOException - the position cannot be updated. This may be because the channel only supports block aligned IO and the current position is not block aligned.
      • size

        long size()
           throws java.io.IOException
        Get the total size of the channel.

        Prior to reading from a channel the size might not yet be known. Implementors may return -1 until after the first read method call. Once a read has been completed, the underlying file size should be available.

        Returns:
        r total size of the channel; -1 if not yet available.
        Throws:
        java.io.IOException - the size cannot be determined.
      • blockSize

        int blockSize()
        Get the recommended alignment for reads.

        Starting a read at multiples of the blockSize is more efficient than starting a read at any other position. If 0 or -1 the channel does not have any specific block size recommendation.

        Channels should not recommend large block sizes. Sizes up to 1-4 MiB may be reasonable, but sizes above that may be horribly inefficient. The DfsBlockCache favors the alignment suggested by the channel rather than the configured size under the assumption that reads are very expensive and the channel knows what size is best to access it with.

        Returns:
        recommended alignment size for randomly positioned reads. Does not need to be a power of 2.