IT. Expert System.

Java Standard Edition (SE)

DatagramChannel


compact1, compact2, compact3
java.nio.channels

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:

    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 Detail

      • DatagramChannel

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

      • 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
      • 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.

        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
      • 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()
      • socket

        public abstract DatagramSocket socket()
        Retrieves a datagram socket associated with this channel.

        The returned object will not declare any public methods that are not declared in the DatagramSocket class.

        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. A datagram 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.

        This method may be invoked at any time. It will not have any effect on read or write operations that are already in progress at the moment that it is invoked. 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:
        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
        SecurityException - If a security manager has been installed and it does not permit access to the given remote address
        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. It will not have any effect on read or write operations that are already in progress at the moment that it is invoked.

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

        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. 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:
        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 a security manager has been installed and it does not permit datagrams to be accepted from the datagram's sender
        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:
        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 a security manager has been installed and it does not permit datagrams to be sent to the given address
        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


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