NioSocket抽象类

public abstract class SelectableChannel extends AbstractChannel implements Channel
{
    public abstract void configureBlocking (boolean block) throws IOException;
    public abstract boolean isBlocking( );
    public abstract Object blockingLock( );
}

public abstract class ServerSocketChannel extends AbstractSelectableChannel
{
    public static ServerSocketChannel open( ) throws IOException
    public abstract ServerSocket socket( );
    public abstract ServerSocket accept( ) throws IOException;
    public final int validOps( )
}

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public abstract class SocketChannel extends AbstractSelectableChannel 
    implements ByteChannel, ScatteringByteChannel, GatheringByteChannel
{
    public static SocketChannel open( ) throws IOException
    public static SocketChannel open (InetSocketAddress remote)
    throws IOException
    public abstract Socket socket( );
    public abstract boolean connect (SocketAddress remote)
    throws IOException;
    public abstract boolean isConnectionPending( );
    public abstract boolean finishConnect( ) throws IOException;
    public abstract boolean isConnected( );
    public final int validOps( )
}

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Create:

ServerSocketChannel.open() or SocketChannel.open()

SocketChannel.socket() -> Socket
Socket.getChannel() -> SocketChannel

虽然每个SocketChannel对象都会创建一个对等的Socket对象,反过来却不成
立。直接创建的Socket对象不会关联SocketChannel对象,它们的getChannel( )
方法只返回null。

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public abstract class DatagramChannel extends AbstractSelectableChannel
    implements ByteChannel, ScatteringByteChannel, GatheringByteChannel
{
    public static DatagramChannel open( ) throws IOException;
    public abstract DatagramSocket socket( );
    public abstract DatagramChannel connect (SocketAddress remote) throws IOException;
    public abstract boolean isConnected( );
    public abstract DatagramChannel disconnect( ) throws IOException;
    public abstract SocketAddress receive (ByteBuffer dst) throws IOException;
    public abstract int send (ByteBuffer src, SocketAddress target);
    public abstract int read (ByteBuffer dst) throws IOException;
    public abstract long read (ByteBuffer [] dsts) throws IOException;
    public abstract long read (ByteBuffer [] dsts, int offset, int length) throws IOException;
    public abstract int write (ByteBuffer src) throws IOException;
    public abstract long write(ByteBuffer[] srcs) throws IOException;
    public abstract long write(ByteBuffer[] srcs, int offset, int length) throws IOException;
    public abstract SocketAddress receive (ByteBuffer dst) throws IOException;
    public abstract int send (ByteBuffer src, SocketAddress target);
}

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channel.send (buffer, addr);
addr = receivePacket (channel, buffer);
this.channel.socket( ).bind (new InetSocketAddress (port));

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FileChannel fc = raf.getChannel( );
FileLock lock = fc.lock (INDEX_START, INDEX_SIZE, false);
lock.release( );

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public abstract class SelectableChannel extends AbstractChannel implements Channel
{
    public abstract SelectionKey register (Selector sel, int ops) throws ClosedChannelException;
    public abstract SelectionKey register (Selector sel, int ops, Object att) throws ClosedChannelException;
    public abstract boolean isRegistered( );
    abstract SelectionKey keyFor (Selector sel);
    abstract int validOps( );
    abstract void configureBlocking (boolean block) IOException;
    abstract boolean isBlocking( );
    abstract Object blockingLock( );
}

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public abstract class Selector
{
    public static Selector open( ) throws IOException
    public abstract boolean isOpen( );
    public abstract void close( ) throws IOException;
    public abstract SelectionProvider provider( );
    public abstract int select( ) throws IOException;
    public abstract int select (long timeout) throws IOException;
    public abstract int selectNow( ) throws IOException;
    public abstract void wakeup( );
    public abstract Set keys( );
    public abstract Set selectedKeys( );
}

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public abstract class SelectionKey
{
    public static final int OP_READ
    public static final int OP_WRITE
    public static final int OP_CONNECT
    public static final int OP_ACCEPT
    public abstract SelectableChannel channel( );
    public abstract Selector selector( );
    public abstract void cancel( );
    public abstract boolean isValid( );
    public abstract int interestOps( );
    public abstract void interestOps (int ops);
    public abstract int readyOps( );
    public final boolean isReadable( )
    public final boolean isWritable( )
    public final boolean isConnectable( )
    public final boolean isAcceptable( )
    public final Object attach (Object ob)
    public final Object attachment( )
}

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选择器包含了注册到它们之上的通道的集合。在任意给定的时间里,对于一个给定的选择器和
一个给定的通道而言,只有一种注册关系是有效的。但是,将一个通道注册到多于一个的选择器上
允许的。这么做的话,在更新interest集合为指定的值的同时,将返回与之前相同的选择键。实际
上,后续的注册都只是简单地将与之前的注册关系相关的键进行更新。

一个例外的情形是当您试图将一个通道注册到一个相关的键已经被取消的选择器上,而通道仍
然处于被注册的状态的时候。通道不会在键被取消的时候立即注销。直到下一次操作发生为止,它
们仍然会处于被注册的状态。在这种情况下,未检查的CancelledKeyException将
会被抛出。请务必在键可能被取消的情况下检查SelectionKey对象的状态。

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有 四 种被 定 义 的 可 选 择 操 作 :读 (read) , 写 (write), 连 接 (connect) 和 接 受(accept)

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最简单的状态测试方法是：
SelectionKey.isAcceptable()   等价于 ((key.readyOps( ) & SelectionKey.OP_ACCEPT) != 0
SelectionKey.isConnectable()   等价于 ((key.readyOps( ) & SelectionKey.OP_CONNECT) != 0
SelectionKey.isReadable()   等价于 ((key.readyOps( ) & SelectionKey.OP_READ) != 0
SelectionKey.isWritable()   等价于 ((key.readyOps( ) & SelectionKey.OP_WRITE) != 0