public abstract long transferTo (long position, long count, WritableByteChannel target) throws IOException

Transfers bytes from this channel's file to the given writable byte channel.

An attempt is made to read up to count bytes starting at the given position in this channel's file and write them to the target channel. An invocation of this method may or may not transfer all of the requested bytes; whether or not it does so depends upon the natures and states of the channels. Fewer than the requested number of bytes are transferred if this channel's file contains fewer than count bytes starting at the given position, or if the target channel is non-blocking and it has fewer than count bytes free in its output buffer.

This method does not modify this channel's position. If the given position is greater than the file's current size then no bytes are transferred. If the target channel has a position then bytes are written starting at that position and then the position is incremented by the number of bytes written.

This method is potentially much more efficient than a simple loop that reads from this channel and writes to the target channel. Many operating systems can transfer bytes directly from the filesystem cache to the target channel without actually copying them.

Parameters:
position     The position within the file at which the transfer is to begin; must be non-negative
count     The maximum number of bytes to be transferred; must be non-negative
target     The target channel

Returns:  The number of bytes, possibly zero, that were actually transferred

Exceptions:
IllegalArgumentException     If the preconditions on the parameters do not hold
NonReadableChannelException     If this channel was not opened for reading
NonWritableChannelException     If the target channel was not opened for writing
ClosedChannelException     If either this channel or the target channel is closed
AsynchronousCloseException     If another thread closes either channel while the transfer is in progress
ClosedByInterruptException     If another thread interrupts the current thread while the transfer is in progress, thereby closing both channels and setting the current thread's interrupt status
IOException     If some other I/O error occurs