Datagram channels are not a complete abstraction of network datagram * sockets. Binding and the manipulation of socket options must be done * through an associated {@link java.net.DatagramSocket} object obtained by * invoking the {@link #socket() socket} method. It is not possible to create * a channel for an arbitrary, pre-existing datagram socket, nor is it possible * to specify the {@link java.net.DatagramSocketImpl} object to be used by a * datagram socket associated with a datagram channel. * *
A datagram channel is created by invoking the {@link #open 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 {@link #send send} * and {@link #receive receive} methods to be used. A datagram channel may be * connected, by invoking its {@link #connect 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 {@link #read(java.nio.ByteBuffer) read} and {@link * #write(java.nio.ByteBuffer) 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 {@link #isConnected 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.
* * * @author Mark Reinhold * @author JSR-51 Expert Group * @version 1.32, 03/12/19 * @since 1.4 */ public abstract class DatagramChannel extends AbstractSelectableChannel implements ByteChannel, ScatteringByteChannel, GatheringByteChannel { /** * Initializes a new instance of this class. */ protected DatagramChannel(SelectorProvider provider) { super(provider); } /** * Opens a datagram channel. * *The new channel is created by invoking the {@link * java.nio.channels.spi.SelectorProvider#openDatagramChannel() * openDatagramChannel} method of the system-wide default {@link * java.nio.channels.spi.SelectorProvider} object. The channel will not be * connected.
* * @return A new datagram channel * * @throws IOException * If an I/O error occurs */ public static DatagramChannel open() throws IOException { return SelectorProvider.provider().openDatagramChannel(); } /** * Returns an operation set identifying this channel's supported * operations. * *Datagram channels support reading and writing, so this method * returns ({@link SelectionKey#OP_READ} | {@link * SelectionKey#OP_WRITE}).
* * @return The valid-operation set */ public final int validOps() { return (SelectionKey.OP_READ | SelectionKey.OP_WRITE); } // -- Socket-specific operations -- /** * Retrieves a datagram socket associated with this channel. * *The returned object will not declare any public methods that are not * declared in the {@link java.net.DatagramSocket} class.
* * @return A datagram socket associated with this channel */ public abstract DatagramSocket socket(); /** * Tells whether or not this channel's socket is connected. * * @return true if, and only if, this channel's socket * is connected */ public abstract boolean isConnected(); /** * 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 {@link * java.net.DatagramSocket#connect connect} method of the {@link * java.net.DatagramSocket} class. That is, if a security manager has been * installed then this method verifies that its {@link * java.lang.SecurityManager#checkAccept checkAccept} and {@link * java.lang.SecurityManager#checkConnect 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.
* * @param remote * The remote address to which this channel is to be connected * * @return This datagram channel * * @throws ClosedChannelException * If this channel is closed * * @throws AsynchronousCloseException * If another thread closes this channel * while the connect operation is in progress * * @throws 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 * * @throws SecurityException * If a security manager has been installed * and it does not permit access to the given remote address * * @throws IOException * If some other I/O error occurs */ public abstract DatagramChannel connect(SocketAddress remote) 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.
* * @return This datagram channel * * @throws IOException * If some other I/O error occurs */ public abstract DatagramChannel disconnect() 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 {@link * ReadableByteChannel#read(java.nio.ByteBuffer) 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 {@link * java.net.DatagramSocket#receive receive} method of the {@link * java.net.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 {@link * java.lang.SecurityManager#checkAccept checkAccept} method. The overhead * of this security check can be avoided by first connecting the socket via * the {@link #connect 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.
* * @param dst * The buffer into which the datagram is to be transferred * * @return 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 * * @throws AsynchronousCloseException * If another thread closes this channel * while the read operation is in progress * * @throws 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 * * @throws SecurityException * If a security manager has been installed * and it does not permit datagrams to be accepted * from the datagram's sender * * @throws IOException * If some other I/O error occurs */ public abstract SocketAddress receive(ByteBuffer dst) 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 * {@link WritableByteChannel#write(java.nio.ByteBuffer) write} operation. * *
This method performs exactly the same security checks as the {@link * java.net.DatagramSocket#send send} method of the {@link * java.net.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 {@link * java.lang.SecurityManager#checkConnect checkConnect} method. The * overhead of this security check can be avoided by first connecting the * socket via the {@link #connect 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.
* * @param src * The buffer containing the datagram to be sent * * @param target * The address to which the datagram is to be sent * * @return 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 * * @throws AsynchronousCloseException * If another thread closes this channel * while the read operation is in progress * * @throws 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 * * @throws SecurityException * If a security manager has been installed * and it does not permit datagrams to be sent * to the given address * * @throws IOException * If some other I/O error occurs */ public abstract int send(ByteBuffer src, SocketAddress target) throws IOException; // -- ByteChannel operations -- /** * 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 {@link * ReadableByteChannel} interface.
* * @throws NotYetConnectedException * If this channel's socket is not connected */ 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 buffers * then the remainder of the datagram is silently discarded. Otherwise * this method behaves exactly as specified in the {@link * ScatteringByteChannel} interface.
* * @throws NotYetConnectedException * If this channel's socket is not connected */ 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 {@link * ScatteringByteChannel} interface.
* * @throws NotYetConnectedException * If this channel's socket is not connected */ public final long read(ByteBuffer[] dsts) throws IOException { return read(dsts, 0, dsts.length); } /** * 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 {@link * WritableByteChannel} interface.
* * @throws NotYetConnectedException * If this channel's socket is not connected */ 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 {@link * GatheringByteChannel} interface.
* * @return 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 */ 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 {@link * GatheringByteChannel} interface.
* * @return 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 */ public final long write(ByteBuffer[] srcs) throws IOException { return write(srcs, 0, srcs.length); } }