Only one read operation upon a readable channel may be in progress at * any given time. If one thread initiates a read operation upon a channel * then any other thread that attempts to initiate another read operation will * block until the first operation is complete. Whether or not other kinds of * I/O operations may proceed concurrently with a read operation depends upon * the type of the channel.
* * * @author Mark Reinhold * @author JSR-51 Expert Group * @version 1.16, 03/12/19 * @since 1.4 */ public interface ReadableByteChannel extends Channel { /** * Reads a sequence of bytes from this channel into the given buffer. * *An attempt is made to read up to r bytes from the channel, * where r is the number of bytes remaining in the buffer, that is, * dst.remaining(), at the moment this method is invoked. * *
Suppose that a byte sequence of length n is read, where * 0 <= n <= r. * This byte sequence will be transferred into the buffer so that the first * byte in the sequence is at index p and the last byte is at index * p + n - 1, * where p is the buffer's position at the moment this method is * invoked. Upon return the buffer's position will be equal to * p + n; its limit will not have changed. * *
A read operation might not fill the buffer, and in fact it might not * read any bytes at all. Whether or not it does so depends upon the * nature and state of the channel. A socket channel in non-blocking mode, * for example, cannot read any more bytes than are immediately available * from the socket's input buffer; similarly, a file channel cannot read * any more bytes than remain in the file. It is guaranteed, however, that * if a channel is in blocking mode and there is at least one byte * remaining in the buffer then this method will block until at least one * byte is read. * *
This method may be invoked at any time. If another thread has * already initiated a read operation upon this channel, however, then an * invocation of this method will block until the first operation is * complete.
* * @param dst * The buffer into which bytes are to be transferred * * @return The number of bytes read, possibly zero, or -1 if the * channel has reached end-of-stream * * @throws NonReadableChannelException * If this channel was not opened for reading * * @throws ClosedChannelException * If this channel is closed * * @throws AsynchronousCloseException * If another thread closes this channel * while the read operation is in progress * * @throws ClosedByInterruptException * If another thread interrupts the current thread * while the read operation is in progress, thereby * closing the channel and setting the current thread's * interrupt status * * @throws IOException * If some other I/O error occurs */ public int read(ByteBuffer dst) throws IOException; }