Java in a Nutshell, 5th Edition [Electronic resources] نسخه متنی

This
class
is a channel for communicating over a
java.net.Socket. It implements
ReadableByteChannel and
WriteableByteChannel as well as
GatheringByteChannel and
ScatteringByteChannel. It is a subclass of
SelectableChannel and can be used with a
Selector.

Create a new SocketChannel with one of the static
open( ) methods. The no-argument version of
open( ) creates a new
SocketChannel but does not connect it to a remote
host. The other version of open( ) opens a new
channel and connects it to the specified
java.net.SocketAddress. If you create an
unconnected socket, you can explictly connect it with the
connect( ) method. The main reason to open the
channel and connect to the remote host in separate steps is if you
want to do a nonblocking
connect. To do this, first put the channel into nonblocking mode with
the inherited configureBlocking(
)
method. Then, call connect(
): it
will return immediately, without waiting for the connection to be
established. Then register the channel with a
Selector specifying that you are interested in
SelectionKey.OP_CONNECT operations. When you are
notified that your channel is ready to connect (see
Selector and SelectionKey for
details) simply call the nonblocking finishConnect(
) method to complete the connection. isConnected(
) returns TRue once a connection is
established, and false otherwise.
isConnectionPending( ) returns
true if connect( ) has been
called in blocking mode and has not yet returned, or if
connect( ) has been called in nonblocking mode,
but finishConnect( ) has not been called yet.

Once you have opened and connected a
SocketChannel, you can read and write bytes to it
with the various read( )
and write( )
methods. SocketChannel is thread-safe: read and
write operations may proceed concurrently, but
SocketChannel will not allow more than one read
operation and more than one write operation to proceed at the same
time. If you place a SocketChannel into
nonblocking mode, you can register it with a
Selector using the SelectionKey
constants OP_READ and OP_WRITE,
to have the Selector tell you when the channel is
ready for reading or writing.

The socket( )
method returns the java.net.Socket that is
associated with the SocketChannel. You can use
this Socket object to configure socket options,
bind the socket to a specific local address, close the socket, or
shutdown its input or output sides. See
java.net.Socket. Note that although all
SocketChannel objects have associated
Socket objects, the reverse is not true: you
cannot obtain a SocketChannel from a
Socket unless the Socket was
created along with the SocketChannel by a call to
SocketChannel.open( ).

When you are done with a SocketChannel, close it
with the close( )
method. You can also independently shut down the read and write
portions of the channel with socket( ).shutdownInput(
) and socket( ).shutdownOutput( ). When
the input is shut down, any future reads (and any blocked read
operation) will return -1 to indicate that the end-of-stream has been
reached. When the output is shut down, any future writes throw a
ClosedChannelException, and any write operation
that was blocked at the time of shut down throws a
AsynchronousCloseException.

Figure 13-39. java.nio.channels.SocketChannel

public abstract class

SocketChannel extends java.nio.channels.spi.
AbstractSelectableChannel
implements ByteChannel, GatheringByteChannel, ScatteringByteChannel {
// Protected Constructors
protected

SocketChannel (java.nio.channels.spi.SelectorProvider

provider );
// Public Class Methods
public static SocketChannel

open ( ) throws java.io.IOException;
public static SocketChannel

open (java.net.SocketAddress

remote )
throws java.io.IOException;
// Public Instance Methods
public abstract boolean

connect (java.net.SocketAddress

remote )
throws java.io.IOException;
public abstract boolean

finishConnect ( ) throws java.io.IOException;
public abstract boolean

isConnected ( );
public abstract boolean

isConnectionPending ( );
public abstract java.net.Socket

socket ( );
// Methods Implementing GatheringByteChannel
public final long

write (java.nio.ByteBuffer[ ]

srcs )
throws java.io.IOException;
public abstract long

write (java.nio.ByteBuffer[ ]

srcs , int

offset ,
int

length ) throws java.io.IOException;
// Methods Implementing ReadableByteChannel
public abstract int

read (java.nio.ByteBuffer

dst )
throws java.io.IOException;
// Methods Implementing ScatteringByteChannel
public final long

read (java.nio.ByteBuffer[ ]

dsts )
throws java.io.IOException;
public abstract long

read (java.nio.ByteBuffer[ ]

dsts , int

offset ,
int

length ) throws java.io.IOException;
// Methods Implementing WritableByteChannel
public abstract int

write (java.nio.ByteBuffer

src )
throws java.io.IOException;
// Public Methods Overriding SelectableChannel
public final int

validOps ( );
}

Returned By

java.net.Socket.getChannel( ),
ServerSocketChannel.accept( ),
java.nio.channels.spi.SelectorProvider.openSocketChannel(
)