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## java.nio.channels
Class DatagramChannel

    java.lang.Object
      |
      +--java.nio.channels.spi.AbstractInterruptibleChannel
            |
            +--java.nio.channels.SelectableChannel
                  |
                  +--java.nio.channels.spi.AbstractSelectableChannel
                        |
                        +--java.nio.channels.DatagramChannel

All Implemented Interfaces:
  ByteChannel, Channel, GatheringByteChannel, InterruptibleChannel, ReadableByteChannel, ScatteringByteChannel, WritableByteChannel

public abstract class DatagramChannel
extends AbstractSelectableChannel
implements ByteChannel, ScatteringByteChannel, GatheringByteChannel

A selectable channel for datagram-oriented sockets.

Datagram channels are not a complete abstraction of network datagram sockets. Binding and the manipulation of socket options must be done through an associated `DatagramSocket` object obtained by invoking the `socket` method. It is not possible to create a channel for an arbitrary, pre-existing datagram socket, nor is it possible to specify the `DatagramSocketImpl` object to be used by a datagram socket associated with a datagram channel.

A datagram channel is created by invoking the `open` method of this class. 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.

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 Summary
`protected` | `DatagramChannel(SelectorProvider provider)` Initializes a new instance of this class.

Method Summary
`abstract DatagramChannel` | `connect(SocketAddress remote)` Connects this channel's socket.
`abstract DatagramChannel` | `disconnect()` Disconnects this channel's socket.
`abstract boolean` | `isConnected()` Tells whether or not this channel's socket is connected.
`static DatagramChannel` | `open()` Opens a datagram channel.
`abstract int` | `read(ByteBuffer dst)` Reads a datagram from this channel.
`long` | `read(ByteBuffer[] dsts)` Reads a datagram from this channel.
`abstract long` | `read(ByteBuffer[] dsts, int offset, int length)` Reads a datagram from this channel.
`abstract SocketAddress` | `receive(ByteBuffer dst)` Receives a datagram via this channel.
`abstract int` | `send(ByteBuffer src, SocketAddress target)` Sends a datagram via this channel.
`abstract DatagramSocket` | `socket()` Retrieves a datagram socket associated with this channel.
`int` | `validOps()` Returns an operation set identifying this channel's supported operations.
`abstract int` | `write(ByteBuffer src)` Writes a datagram to this channel.
`long` | `write(ByteBuffer[] srcs)` Writes a datagram to this channel.
`abstract long` | `write(ByteBuffer[] srcs, int offset, int length)` Writes a datagram to this channel.

Methods inherited from class java.nio.channels.spi.AbstractSelectableChannel
`blockingLock, configureBlocking, implCloseChannel, implCloseSelectableChannel, implConfigureBlocking, isBlocking, isRegistered, keyFor, provider, register`

Methods inherited from class java.nio.channels.SelectableChannel
`register`

Methods inherited from class java.nio.channels.spi.AbstractInterruptibleChannel
`begin, close, end, isOpen`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Methods inherited from interface java.nio.channels.Channel
`close, isOpen`

Constructor Detail

### DatagramChannel

    protected DatagramChannel(SelectorProvider provider)

  Initializes a new instance of this class.

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.

  Returns:
    A new datagram channel
  Throws:
    `IOException` - If an I/O error occurs

### 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

### 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 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.

  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

### 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.

  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.

  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
    `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
    `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
    `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
    `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
    `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
    `IOException` - If some other I/O error occurs

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