Package java.nio.channels

Class SocketChannel

java.lang.Object
java.nio.channels.spi.AbstractInterruptibleChannel
java.nio.channels.SelectableChannel
java.nio.channels.spi.AbstractSelectableChannel
java.nio.channels.SocketChannel
All Implemented Interfaces:
Closeable, AutoCloseable, ByteChannel, Channel, GatheringByteChannel, InterruptibleChannel, ReadableByteChannel, ScatteringByteChannel, WritableByteChannel
public abstract class SocketChannel
extends AbstractSelectableChannel
implements ByteChannel, ScatteringByteChannel, GatheringByteChannel
A SocketChannel is a selectable channel that provides a partial abstraction of stream connecting socket. socket() returns the related Socket instance which can handle the socket.

A socket channel is open but not connected when created by open(). After connecting it by calling connect(SocketAddress), it will remain connected until it gets closed. If the connection is non-blocking then connect(SocketAddress) is used to initiate the connection, followed by a call of finishConnect() to perform the final steps of connecting. isConnectionPending() indicates if the connection is blocked or not; isConnected() indicates if the socket is finally connected or not.

The input and output sides of a channel can be shut down independently and asynchronously without closing the channel. The shutdownInput method is used for the input side of a channel and subsequent read operations return -1, which means end of stream. If another thread is blocked in a read operation when the shutdown occurs, the read will end without effect and return end of stream. The shutdownOutput method is used for the output side of the channel; subsequent write operations throw a ClosedChannelException. If the output is shut down and another thread is blocked in a write operation, an AsynchronousCloseException will be thrown to the pending thread.

Socket channels are thread-safe, no more than one thread can read or write at any given time. The connect(SocketAddress) and finishConnect() methods are synchronized against each other; when they are processing, calls to read and write will block.

  • Constructor Details

    • SocketChannel

      protected SocketChannel​(SelectorProvider selectorProvider)
      Constructs a new SocketChannel.
      Parameters:
      selectorProvider - an instance of SelectorProvider.

  • Method Details

    • open

      public static SocketChannel open() throws IOException
      Creates an open and unconnected socket channel.

      This channel is created by calling openSocketChannel() of the default SelectorProvider instance.

      Returns:
      the new channel which is open but unconnected.
      Throws:
      IOException - if an I/O error occurs.

    • open

      public static SocketChannel open​(SocketAddress address) throws IOException
      Creates a socket channel and connects it to a socket address.

      This method performs a call to open() followed by a call to connect(SocketAddress).

      Parameters:
      address - the socket address to be connected to.
      Returns:
      the new connected channel.
      Throws:
      AsynchronousCloseException - if this channel is closed by another thread while this method is executing.
      ClosedByInterruptException - if another thread interrupts the calling thread while this operation is executing. The calling thread will have the interrupt state set and the channel will be closed.
      UnresolvedAddressException - if the address is not resolved.
      UnsupportedAddressTypeException - if the address type is not supported.
      IOException - if an I/O error occurs.

    • validOps

      public final int validOps()
      Gets the valid operations of this channel. Socket channels support connect, read and write operation, so this method returns SelectionKey.OP_CONNECT | SelectionKey.OP_READ | SelectionKey.OP_WRITE.
      Specified by:
      validOps in class SelectableChannel
      Returns:
      the operations supported by this channel.
      See Also:
      SelectableChannel.validOps()

    • socket

      public abstract Socket socket()
      Returns the socket assigned to this channel, which does not declare any public methods that are not declared in Socket.
      Returns:
      the socket assigned to this channel.

    • isConnected

      public abstract boolean isConnected()
      Indicates whether this channel's socket is connected.
      Returns:
      true if this channel's socket is connected, false otherwise.

    • isConnectionPending

      public abstract boolean isConnectionPending()
      Indicates whether this channel's socket is still trying to connect.
      Returns:
      true if the connection is initiated but not finished; false otherwise.

    • connect

      public abstract boolean connect​(SocketAddress address) throws IOException
      Connects this channel's socket with a remote address.

      If this channel is blocking, this method will suspend until connecting is finished or an I/O exception occurs. If the channel is non-blocking, this method will return true if the connection is finished at once or return false when the connection must be finished later by calling finishConnect().

      This method can be called at any moment and can block other read and write operations while connecting. It executes the same security checks as the connect method of the Socket class.

      Parameters:
      address - the address to connect with.
      Returns:
      true if the connection is finished, false otherwise.
      Throws:
      AlreadyConnectedException - if the channel is already connected.
      ConnectionPendingException - a non-blocking connecting operation is already executing on this channel.
      ClosedChannelException - if this channel is closed.
      AsynchronousCloseException - if this channel is closed by another thread while this method is executing.
      ClosedByInterruptException - if another thread interrupts the calling thread while this operation is in progress. The calling thread will have the interrupt state set and this channel will be closed.
      UnresolvedAddressException - if the address is not resolved.
      UnsupportedAddressTypeException - if the address type is not supported.
      IOException - if an I/O error occurs.

    • finishConnect

      public abstract boolean finishConnect() throws IOException
      Completes the connection process initiated by a call of connect(SocketAddress).

      This method returns true if the connection is finished already and returns false if the channel is non-blocking and the connection is not finished yet.

      If this channel is in blocking mode, this method will suspend and return true when the connection is finished. It closes this channel and throws an exception if the connection fails.

      This method can be called at any moment and it can block other read and write operations while connecting.

      Returns:
      true if the connection is successfully finished, false otherwise.
      Throws:
      NoConnectionPendingException - if the channel is not connected and the connection process has not been initiated.
      ClosedChannelException - if this channel is closed.
      AsynchronousCloseException - if this channel is closed by another thread while this method is executing.
      ClosedByInterruptException - if another thread interrupts the calling thread while this operation is in progress. The calling thread has the interrupt state set, and this channel is closed.
      IOException - if an I/O error occurs.

    • read

      public abstract int read​(ByteBuffer target) throws IOException
      Reads bytes from this socket channel into the given buffer.

      The maximum number of bytes that will be read is the remaining number of bytes in the buffer when the method is invoked. The bytes will be copied into the buffer starting at the buffer's current position.

      The call may block if other threads are also attempting to read from this channel.

      Upon completion, the buffer's position is set to the end of the bytes that have been read. The buffer's limit is not changed.

      Specified by:
      read in interface ReadableByteChannel
      Parameters:
      target - the byte buffer to receive the bytes.
      Returns:
      the number of bytes actually read.
      Throws:
      AsynchronousCloseException - if another thread closes the channel during the read.
      NotYetConnectedException - if this channel is not yet connected.
      ClosedByInterruptException - if another thread interrupts the calling thread while this operation is in progress. The interrupt state of the calling thread is set and the channel is closed.
      ClosedChannelException - if this channel is closed.
      IOException - if another I/O error occurs.
      See Also:
      ReadableByteChannel.read(java.nio.ByteBuffer)

    • read

      public abstract long read​(ByteBuffer[] targets, int offset, int length) throws IOException
      Reads bytes from this socket channel into a subset of the given buffers. This method attempts to read all remaining() bytes from length byte buffers, in order, starting at targets[offset]. The number of bytes actually read is returned.

      If a read operation is in progress, subsequent threads will block until the read is completed and will then contend for the ability to read.

      Specified by:
      read in interface ScatteringByteChannel
      Parameters:
      targets - the array of byte buffers into which the bytes will be copied.
      offset - the index of the first buffer to store bytes in.
      length - the maximum number of buffers to store bytes in.
      Returns:
      the number of bytes actually read.
      Throws:
      AsynchronousCloseException - if this channel is closed by another thread during this read operation.
      ClosedByInterruptException - if another thread interrupts the calling thread while this operation is in progress. The interrupt state of the calling thread is set and the channel is closed.
      ClosedChannelException - if this channel is closed.
      IndexOutOfBoundsException - if offset < 0 or length < 0, or if offset + length is greater than the size of targets.
      IOException - if another I/O error occurs.
      NotYetConnectedException - if this channel is not yet connected.
      See Also:
      ScatteringByteChannel.read(java.nio.ByteBuffer[], int, int)

    • read

      public final long read​(ByteBuffer[] targets) throws IOException
      Reads bytes from this socket channel and stores them in the specified array of buffers. This method attempts to read as many bytes as can be stored in the buffer array from this channel and returns the number of bytes actually read.

      If a read operation is in progress, subsequent threads will block until the read is completed and will then contend for the ability to read.

      Calling this method is equivalent to calling read(targets, 0, targets.length);

      Specified by:
      read in interface ScatteringByteChannel
      Parameters:
      targets - the array of byte buffers into which the bytes will be copied.
      Returns:
      the number of bytes actually read.
      Throws:
      AsynchronousCloseException - if this channel is closed by another thread during this read operation.
      ClosedByInterruptException - if another thread interrupts the calling thread while this operation is in progress. The interrupt state of the calling thread is set and the channel is closed.
      ClosedChannelException - if this channel is closed.
      IOException - if another I/O error occurs.
      NotYetConnectedException - if this channel is not yet connected.

    • write

      public abstract int write​(ByteBuffer source) throws IOException
      Writes bytes from the given byte buffer to this socket channel. The maximum number of bytes that are written is the remaining number of bytes in the buffer when this method is invoked. The bytes are taken from the buffer starting at the buffer's position.

      The call may block if other threads are also attempting to write to the same channel.

      Upon completion, the buffer's position is updated to the end of the bytes that have been written. The buffer's limit is not changed.

      Specified by:
      write in interface WritableByteChannel
      Parameters:
      source - the byte buffer containing the bytes to be written.
      Returns:
      the number of bytes actually written.
      Throws:
      AsynchronousCloseException - if another thread closes the channel during the write.
      ClosedByInterruptException - if another thread interrupts the calling thread while this operation is in progress. The interrupt state of the calling thread is set and the channel is closed.
      ClosedChannelException - if the channel was already closed.
      IOException - if another I/O error occurs.
      NotYetConnectedException - if this channel is not connected yet.
      See Also:
      WritableByteChannel.write(java.nio.ByteBuffer)

    • write

      public abstract long write​(ByteBuffer[] sources, int offset, int length) throws IOException
      Attempts to write a subset of the given bytes from the buffers to this socket channel. This method attempts to write all remaining() bytes from length byte buffers, in order, starting at sources[offset]. The number of bytes actually written is returned.

      If a write operation is in progress, subsequent threads will block until the write is completed and then contend for the ability to write.

      Specified by:
      write in interface GatheringByteChannel
      Parameters:
      sources - the array of byte buffers that is the source for bytes written to this channel.
      offset - the index of the first buffer in buffers to get bytes from.
      length - the number of buffers to get bytes from.
      Returns:
      the number of bytes actually written to this channel.
      Throws:
      AsynchronousCloseException - if this channel is closed by another thread during this write operation.
      ClosedByInterruptException - if another thread interrupts the calling thread while this operation is in progress. The interrupt state of the calling thread is set and the channel is closed.
      ClosedChannelException - if this channel is closed.
      IndexOutOfBoundsException - if offset < 0 or length < 0, or if offset + length is greater than the size of sources.
      IOException - if another I/O error occurs.
      NotYetConnectedException - if this channel is not yet connected.
      See Also:
      GatheringByteChannel.write(java.nio.ByteBuffer[], int, int)

    • write

      public final long write​(ByteBuffer[] sources) throws IOException
      Writes bytes from all the given byte buffers to this socket channel.

      Calling this method is equivalent to calling write(sources, 0, sources.length);

      Specified by:
      write in interface GatheringByteChannel
      Parameters:
      sources - the buffers containing bytes to write.
      Returns:
      the number of bytes actually written.
      Throws:
      AsynchronousCloseException - if this channel is closed by another thread during this write operation.
      ClosedByInterruptException - if another thread interrupts the calling thread while this operation is in progress. The interrupt state of the calling thread is set and the channel is closed.
      ClosedChannelException - if this channel is closed.
      IOException - if another I/O error occurs.
      NotYetConnectedException - if this channel is not yet connected.
      See Also:
      GatheringByteChannel.write(java.nio.ByteBuffer[])