GatheringByteChannel (Java SE 26 & JDK 26)
Description: declaration: module: java.base, package: java.nio.channels, interface: GatheringByteChannel
Keywords: java.nio.channels.GatheringByteChannel interface

# Interface GatheringByteChannel

All Superinterfaces:
  `AutoCloseable, Channel, Closeable, WritableByteChannel`

All Known Implementing Classes:
  `DatagramChannel, FileChannel, Pipe.SinkChannel, SocketChannel`

public interface GatheringByteChannel extends WritableByteChannel
A channel that can write bytes from a sequence of buffers.

A gathering write operation writes, in a single invocation, a sequence of bytes from one or more of a given sequence of buffers. Gathering writes are often useful when implementing network protocols or file formats that, for example, group data into segments consisting of one or more fixed-length headers followed by a variable-length body. Similar scattering read operations are defined in the `ScatteringByteChannel` interface.

Since:
  1.4

- ## Method Summary

  Modifier and Type
  Method
  Description
  `long`
  `write(ByteBuffer[] srcs)`
  Writes a sequence of bytes to this channel from the given buffers.
  `long`
  `write(ByteBuffer[] srcs, int offset, int length)`
  Writes a sequence of bytes to this channel from a subsequence of the given buffers.

  ### Methods declared in interface Channel

  `close, isOpen`
  Modifier and Type
  Method
  Description
  `void`
  `close()`
  Closes this channel.
  `boolean`
  `isOpen()`
  Tells whether or not this channel is open.

  ### Methods declared in interface WritableByteChannel

  `write`
  Modifier and Type
  Method
  Description
  `int`
  `write(ByteBuffer src)`
  Writes a sequence of bytes to this channel from the given buffer.

- ## Method Details

  - ### write

    long write(ByteBuffer[] srcs, int offset, int length) throws IOException
    Writes a sequence of bytes to this channel from a subsequence of the given buffers.

    An attempt is made to write up to r bytes to this channel, where r is the total number of bytes remaining in the specified subsequence of the given buffer array, that is,

            srcs[offset].remaining()
                + srcs[offset+1].remaining()
                + ... + srcs[offset+length-1].remaining()

    at the moment that this method is invoked.

    Suppose that a byte sequence of length n is written, where `0` `<=` n `<=` r. Up to the first `srcs[offset].remaining()` bytes of this sequence are written from buffer `srcs[offset]`, up to the next `srcs[offset+1].remaining()` bytes are written from buffer `srcs[offset+1]`, and so forth, until the entire byte sequence is written. As many bytes as possible are written from each buffer, hence the final position of each updated buffer, except the last updated buffer, is guaranteed to be equal to that buffer's limit.

    For many types of channels, a write operation will return only after writing all of the r requested bytes. Some types of channels, depending upon their state, may write only some of the bytes or possibly none at all. A socket channel in non-blocking mode, for example, cannot write any more bytes than are free in the socket's output buffer. The write method may need to be invoked more than once to ensure that all remaining bytes are written.

    This method may be invoked at any time. If another thread has already initiated a write operation upon this channel, however, then an invocation of this method will block until the first operation is complete.

    Parameters:
      `srcs` - The buffers from which bytes are to be retrieved
      `offset` - The offset within the buffer array of the first buffer from which bytes are to be retrieved; must be non-negative and no larger than `srcs.length`
      `length` - The maximum number of buffers to be accessed; must be non-negative and no larger than `srcs.length` - `offset`
    Returns:
      The number of bytes written, possibly zero
    Throws:
      `IndexOutOfBoundsException` - If the preconditions on the `offset` and `length` parameters do not hold
      `NonWritableChannelException` - If this channel was not opened for writing
      `ClosedChannelException` - If this channel is closed
      `AsynchronousCloseException` - If another thread closes this channel while the write operation is in progress
      `ClosedByInterruptException` - If another thread interrupts the current thread while the write operation is in progress, thereby closing the channel and setting the current thread's interrupted status
      `IOException` - If some other I/O error occurs

  - ### write

    long write(ByteBuffer[] srcs) throws IOException
    Writes a sequence of bytes to this channel from the given buffers.

    An invocation of this method of the form `c.write(srcs)` behaves in exactly the same manner as the invocation

            c.write(srcs, 0, srcs.length);

    Parameters:
      `srcs` - The buffers from which bytes are to be retrieved
    Returns:
      The number of bytes written, possibly zero
    Throws:
      `NonWritableChannelException` - If this channel was not opened for writing
      `ClosedChannelException` - If this channel is closed
      `AsynchronousCloseException` - If another thread closes this channel while the write operation is in progress
      `ClosedByInterruptException` - If another thread interrupts the current thread while the write operation is in progress, thereby closing the channel and setting the current thread's interrupted status
      `IOException` - If some other I/O error occurs