Module java.base

Class DatagramChannel

All Implemented Interfaces:
Closeable, AutoCloseable, ByteChannel, Channel, GatheringByteChannel, InterruptibleChannel, MulticastChannel, NetworkChannel, ReadableByteChannel, ScatteringByteChannel, WritableByteChannel

public abstract class DatagramChannel extends AbstractSelectableChannel implements ByteChannel, ScatteringByteChannel, GatheringByteChannel, MulticastChannel
A selectable channel for datagram-oriented sockets.

A datagram channel is created by invoking one of the open methods of this class. It is not possible to create a channel for an arbitrary, pre-existing datagram socket. A newly-created datagram channel is open but not connected. A datagram channel need not be connected in order for the send and receive methods to be used. A datagram channel may be connected, by invoking its connect method, in order to avoid the overhead of the security checks are otherwise performed as part of every send and receive operation. A datagram channel must be connected in order to use the read and write methods, since those methods do not accept or return socket addresses.

Once connected, a datagram channel remains connected until it is disconnected or closed. Whether or not a datagram channel is connected may be determined by invoking its isConnected method.

Socket options are configured using the setOption method. A datagram channel to an Internet Protocol socket supports the following options:

Socket options
Option Name Description
SO_SNDBUF The size of the socket send buffer
SO_RCVBUF The size of the socket receive buffer
SO_REUSEADDR Re-use address
SO_BROADCAST Allow transmission of broadcast datagrams
IP_TOS The Type of Service (ToS) octet in the Internet Protocol (IP) header
IP_MULTICAST_IF The network interface for Internet Protocol (IP) multicast datagrams
IP_MULTICAST_TTL The time-to-live for Internet Protocol (IP) multicast datagrams
IP_MULTICAST_LOOP Loopback for Internet Protocol (IP) multicast datagrams
Additional (implementation specific) options may also be supported.

Datagram channels are safe for use by multiple concurrent threads. They support concurrent reading and writing, though at most one thread may be reading and at most one thread may be writing at any given time.

Since:
1.4
  • Constructor Details

    • DatagramChannel

      protected DatagramChannel(SelectorProvider provider)
      Initializes a new instance of this class.
      Parameters:
      provider - The provider that created this channel
  • Method Details

    • open

      public static DatagramChannel open() throws IOException
      Opens a datagram channel.

      The new channel is created by invoking the openDatagramChannel method of the system-wide default SelectorProvider object. The channel will not be connected.

      The ProtocolFamily of the channel's socket is platform (and possibly configuration) dependent and therefore unspecified. The open allows the protocol family to be selected when opening a datagram channel, and should be used to open datagram channels that are intended for Internet Protocol multicasting.

      Returns:
      A new datagram channel
      Throws:
      IOException - If an I/O error occurs
      See Also:
      java.net.preferIPv4Stack system property
    • open

      public static DatagramChannel open(ProtocolFamily family) throws IOException
      Opens a datagram channel.

      The family parameter is used to specify the ProtocolFamily. If the datagram channel is to be used for IP multicasting then this should correspond to the address type of the multicast groups that this channel will join.

      The new channel is created by invoking the openDatagramChannel method of the system-wide default SelectorProvider object. The channel will not be connected.

      API Note:
      Unix domain sockets are not supported.
      Parameters:
      family - The protocol family
      Returns:
      A new datagram channel
      Throws:
      UnsupportedOperationException - If the specified protocol family is not supported. For example, suppose the parameter is specified as StandardProtocolFamily.INET6 but IPv6 is not enabled on the platform.
      IOException - If an I/O error occurs
      Since:
      1.7
      See Also:
      java.net.preferIPv4Stack system property
    • validOps

      public final int validOps()
      Returns an operation set identifying this channel's supported operations.

      Datagram channels support reading and writing, so this method returns (SelectionKey.OP_READ | SelectionKey.OP_WRITE).

      Specified by:
      validOps in class SelectableChannel
      Returns:
      The valid-operation set
    • bind

      public abstract DatagramChannel bind(SocketAddress local) throws IOException
      Description copied from interface: NetworkChannel
      Binds the channel's socket to a local address.

      This method is used to establish an association between the socket and a local address. Once an association is established then the socket remains bound until the channel is closed. If the local parameter has the value null then the socket will be bound to an address that is assigned automatically.

      Specified by:
      bind in interface NetworkChannel
      Parameters:
      local - The address to bind the socket, or null to bind the socket to an automatically assigned socket address
      Returns:
      This channel
      Throws:
      AlreadyBoundException - If the socket is already bound
      UnsupportedAddressTypeException - If the type of the given address is not supported
      ClosedChannelException - If the channel is closed
      IOException - If some other I/O error occurs
      SecurityException - If a security manager has been installed and its checkListen method denies the operation
      Since:
      1.7
      See Also:
      NetworkChannel.getLocalAddress()
    • setOption

      public abstract <T> DatagramChannel setOption(SocketOption<T> name, T value) throws IOException
      Description copied from interface: NetworkChannel
      Sets the value of a socket option.
      Specified by:
      setOption in interface NetworkChannel
      Type Parameters:
      T - The type of the socket option value
      Parameters:
      name - The socket option
      value - The value of the socket option. A value of null may be a valid value for some socket options.
      Returns:
      This channel
      Throws:
      UnsupportedOperationException - If the socket option is not supported by this channel
      IllegalArgumentException - If the value is not a valid value for this socket option
      ClosedChannelException - If this channel is closed
      IOException - If an I/O error occurs
      Since:
      1.7
      See Also:
      StandardSocketOptions
    • socket

      public abstract DatagramSocket socket()
      Retrieves a datagram socket associated with this channel.
      Returns:
      A datagram socket associated with this channel
    • isConnected

      public abstract boolean isConnected()
      Tells whether or not this channel's socket is connected.
      Returns:
      true if, and only if, this channel's socket is open and connected
    • connect

      public abstract DatagramChannel connect(SocketAddress remote) throws IOException
      Connects this channel's socket.

      The channel's socket is configured so that it only receives datagrams from, and sends datagrams to, the given remote peer address. Once connected, datagrams may not be received from or sent to any other address. Datagrams in the channel's socket receive buffer, which have not been received before invoking this method, may be discarded. The channel's socket remains connected until it is explicitly disconnected or until it is closed.

      This method performs exactly the same security checks as the connect method of the DatagramSocket class. That is, if a security manager has been installed then this method verifies that its checkAccept and checkConnect methods permit datagrams to be received from and sent to, respectively, the given remote address. Once connected, no further security checks are performed for datagrams received from, or sent to, the given remote address. Care should be taken to ensure that a connected datagram channel is not shared with untrusted code.

      This method may be invoked at any time. If another thread has already initiated a read or write operation upon this channel, then an invocation of this method will block until any such operation is complete. If this channel's socket is not bound then this method will first cause the socket to be bound to an address that is assigned automatically, as if invoking the bind method with a parameter of null.

      Parameters:
      remote - The remote address to which this channel is to be connected
      Returns:
      This datagram channel
      Throws:
      AlreadyConnectedException - If this channel is already connected
      ClosedChannelException - If this channel is closed
      AsynchronousCloseException - If another thread closes this channel while the connect operation is in progress
      ClosedByInterruptException - If another thread interrupts the current thread while the connect operation is in progress, thereby closing the channel and setting the current thread's interrupt status
      UnresolvedAddressException - If the given remote address is not fully resolved
      UnsupportedAddressTypeException - If the type of the given remote address is not supported
      SecurityException - If a security manager has been installed and it does not permit access to the given remote address, or if unbound, the security manager checkListen method denies the operation
      IOException - If some other I/O error occurs
    • disconnect

      public abstract DatagramChannel disconnect() throws IOException
      Disconnects this channel's socket.

      The channel's socket is configured so that it can receive datagrams from, and sends datagrams to, any remote address so long as the security manager, if installed, permits it.

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

      If this channel's socket is not connected, or if the channel is closed, then invoking this method has no effect.

      API Note:
      If this method throws an IOException, the channel's socket may be left in an unspecified state. It is strongly recommended that the channel be closed when disconnect fails.
      Returns:
      This datagram channel
      Throws:
      IOException - If some other I/O error occurs
    • getRemoteAddress

      public abstract SocketAddress getRemoteAddress() throws IOException
      Returns the remote address to which this channel's socket is connected.
      Returns:
      The remote address; null if the channel's socket is not connected
      Throws:
      ClosedChannelException - If the channel is closed
      IOException - If an I/O error occurs
      Since:
      1.7
    • receive

      public abstract SocketAddress receive(ByteBuffer dst) throws IOException
      Receives a datagram via this channel.

      If a datagram is immediately available, or if this channel is in blocking mode and one eventually becomes available, then the datagram is copied into the given byte buffer and its source address is returned. If this channel is in non-blocking mode and a datagram is not immediately available then this method immediately returns null.

      The datagram is transferred into the given byte buffer starting at its current position, as if by a regular read operation. If there are fewer bytes remaining in the buffer than are required to hold the datagram then the remainder of the datagram is silently discarded.

      This method performs exactly the same security checks as the receive method of the DatagramSocket class. That is, if the socket is not connected to a specific remote address and a security manager has been installed then for each datagram received this method verifies that the source's address and port number are permitted by the security manager's checkAccept method. Datagrams that are not permitted by the security manager are silently discarded. The overhead of this security check can be avoided by first connecting the socket via the connect method.

      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. If this channel's socket is not bound then this method will first cause the socket to be bound to an address that is assigned automatically, as if invoking the bind method with a parameter of null.

      Parameters:
      dst - The buffer into which the datagram is to be transferred
      Returns:
      The datagram's source address, or null if this channel is in non-blocking mode and no datagram was immediately available
      Throws:
      IllegalArgumentException - If the buffer is read-only
      ClosedChannelException - If this channel is closed
      AsynchronousCloseException - If another thread closes this channel while the read operation is in progress
      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
      SecurityException - If unbound, and a security manager has been installed and its checkListen method denies the operation
      IOException - If some other I/O error occurs
    • send

      public abstract int send(ByteBuffer src, SocketAddress target) throws IOException
      Sends a datagram via this channel.

      If this channel is in non-blocking mode and there is sufficient room in the underlying output buffer, or if this channel is in blocking mode and sufficient room becomes available, then the remaining bytes in the given buffer are transmitted as a single datagram to the given target address.

      The datagram is transferred from the byte buffer as if by a regular write operation.

      This method performs exactly the same security checks as the send method of the DatagramSocket class. That is, if the socket is not connected to a specific remote address and a security manager has been installed then for each datagram sent this method verifies that the target address and port number are permitted by the security manager's checkConnect method. The overhead of this security check can be avoided by first connecting the socket via the connect method.

      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. If this channel's socket is not bound then this method will first cause the socket to be bound to an address that is assigned automatically, as if by invoking the bind method with a parameter of null.

      Parameters:
      src - The buffer containing the datagram to be sent
      target - The address to which the datagram is to be sent
      Returns:
      The number of bytes sent, which will be either the number of bytes that were remaining in the source buffer when this method was invoked or, if this channel is non-blocking, may be zero if there was insufficient room for the datagram in the underlying output buffer
      Throws:
      AlreadyConnectedException - If this channel is connected to a different address from that specified by target
      ClosedChannelException - If this channel is closed
      AsynchronousCloseException - If another thread closes this channel while the read operation is in progress
      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
      UnresolvedAddressException - If the given remote address is not fully resolved
      UnsupportedAddressTypeException - If the type of the given remote address is not supported
      SecurityException - If a security manager has been installed and it does not permit datagrams to be sent to the given address, or if unbound, and the security manager's checkListen method denies the operation
      IOException - If some other I/O error occurs
    • read

      public abstract int read(ByteBuffer dst) throws IOException
      Reads a datagram from this channel.

      This method may only be invoked if this channel's socket is connected, and it only accepts datagrams from the socket's peer. If there are more bytes in the datagram than remain in the given buffer then the remainder of the datagram is silently discarded. Otherwise this method behaves exactly as specified in the ReadableByteChannel interface.

      Specified by:
      read in interface ReadableByteChannel
      Parameters:
      dst - The buffer into which bytes are to be transferred
      Returns:
      The number of bytes read, possibly zero, or -1 if the channel has reached end-of-stream
      Throws:
      NotYetConnectedException - If this channel's socket is not connected
      ClosedChannelException - If this channel is closed
      AsynchronousCloseException - If another thread closes this channel while the read operation is in progress
      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
      IOException - If some other I/O error occurs
    • read

      public abstract long read(ByteBuffer[] dsts, int offset, int length) throws IOException
      Reads a datagram from this channel.

      This method may only be invoked if this channel's socket is connected, and it only accepts datagrams from the socket's peer. If there are more bytes in the datagram than remain in the given buffers then the remainder of the datagram is silently discarded. Otherwise this method behaves exactly as specified in the ScatteringByteChannel interface.

      Specified by:
      read in interface ScatteringByteChannel
      Parameters:
      dsts - The buffers into which bytes are to be transferred
      offset - The offset within the buffer array of the first buffer into which bytes are to be transferred; must be non-negative and no larger than dsts.length
      length - The maximum number of buffers to be accessed; must be non-negative and no larger than dsts.length - offset
      Returns:
      The number of bytes read, possibly zero, or -1 if the channel has reached end-of-stream
      Throws:
      NotYetConnectedException - If this channel's socket is not connected
      ClosedChannelException - If this channel is closed
      AsynchronousCloseException - If another thread closes this channel while the read operation is in progress
      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
      IOException - If some other I/O error occurs
    • read

      public final long read(ByteBuffer[] dsts) throws IOException
      Reads a datagram from this channel.

      This method may only be invoked if this channel's socket is connected, and it only accepts datagrams from the socket's peer. If there are more bytes in the datagram than remain in the given buffers then the remainder of the datagram is silently discarded. Otherwise this method behaves exactly as specified in the ScatteringByteChannel interface.

      Specified by:
      read in interface ScatteringByteChannel
      Parameters:
      dsts - The buffers into which bytes are to be transferred
      Returns:
      The number of bytes read, possibly zero, or -1 if the channel has reached end-of-stream
      Throws:
      NotYetConnectedException - If this channel's socket is not connected
      ClosedChannelException - If this channel is closed
      AsynchronousCloseException - If another thread closes this channel while the read operation is in progress
      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
      IOException - If some other I/O error occurs
    • write

      public abstract int write(ByteBuffer src) throws IOException
      Writes a datagram to this channel.

      This method may only be invoked if this channel's socket is connected, in which case it sends datagrams directly to the socket's peer. Otherwise it behaves exactly as specified in the WritableByteChannel interface.

      Specified by:
      write in interface WritableByteChannel
      Parameters:
      src - The buffer from which bytes are to be retrieved
      Returns:
      The number of bytes written, possibly zero
      Throws:
      NotYetConnectedException - If this channel's socket is not connected
      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 interrupt status
      IOException - If some other I/O error occurs
    • write

      public abstract long write(ByteBuffer[] srcs, int offset, int length) throws IOException
      Writes a datagram to this channel.

      This method may only be invoked if this channel's socket is connected, in which case it sends datagrams directly to the socket's peer. Otherwise it behaves exactly as specified in the GatheringByteChannel interface.

      Specified by:
      write in interface GatheringByteChannel
      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 sent, which will be either the number of bytes that were remaining in the source buffer when this method was invoked or, if this channel is non-blocking, may be zero if there was insufficient room for the datagram in the underlying output buffer
      Throws:
      NotYetConnectedException - If this channel's socket is not connected
      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 interrupt status
      IOException - If some other I/O error occurs
    • write

      public final long write(ByteBuffer[] srcs) throws IOException
      Writes a datagram to this channel.

      This method may only be invoked if this channel's socket is connected, in which case it sends datagrams directly to the socket's peer. Otherwise it behaves exactly as specified in the GatheringByteChannel interface.

      Specified by:
      write in interface GatheringByteChannel
      Parameters:
      srcs - The buffers from which bytes are to be retrieved
      Returns:
      The number of bytes sent, which will be either the number of bytes that were remaining in the source buffer when this method was invoked or, if this channel is non-blocking, may be zero if there was insufficient room for the datagram in the underlying output buffer
      Throws:
      NotYetConnectedException - If this channel's socket is not connected
      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 interrupt status
      IOException - If some other I/O error occurs
    • getLocalAddress

      public abstract SocketAddress getLocalAddress() throws IOException
      Returns the socket address that this channel's socket is bound to.

      Where the channel is bound to an Internet Protocol socket address then the return value from this method is of type InetSocketAddress.

      If there is a security manager set, its checkConnect method is called with the local address and -1 as its arguments to see if the operation is allowed. If the operation is not allowed, a SocketAddress representing the loopback address and the local port of the channel's socket is returned.

      Specified by:
      getLocalAddress in interface NetworkChannel
      Returns:
      The SocketAddress that the socket is bound to, or the SocketAddress representing the loopback address if denied by the security manager, or null if the channel's socket is not bound
      Throws:
      ClosedChannelException - If the channel is closed
      IOException - If an I/O error occurs