ServerSocketChannel定义

Channel接口定义：http://donald-draper.iteye.com/blog/2369111
AbstractInterruptibleChannel接口定义：http://donald-draper.iteye.com/blog/2369238
SelectableChannel接口定义:http://donald-draper.iteye.com/blog/2369317
SelectionKey定义：http://donald-draper.iteye.com/blog/2369499
SelectorProvider定义：http://donald-draper.iteye.com/blog/2369615
AbstractSelectableChannel定义：http://donald-draper.iteye.com/blog/2369742
NetworkChannel接口定义：http://donald-draper.iteye.com/blog/2369773
先来回顾一下ServerSocketChannel继承结构树：

//ServerSocketChannel
public abstract class ServerSocketChannel
    extends AbstractSelectableChannel
    implements NetworkChannel

//AbstractSelectableChannel
public abstract class AbstractSelectableChannel
    extends SelectableChannel

//SelectableChannel
public abstract class SelectableChannel
    extends AbstractInterruptibleChannel
    implements Channel

今天来看一下ServerSocketChannel的定义

package java.nio.channels;

import java.io.IOException;
import java.net.ServerSocket;
import java.net.SocketOption;
import java.net.SocketAddress;
import java.nio.channels.spi.AbstractSelectableChannel;
import java.nio.channels.spi.SelectorProvider;

/**
 * A selectable channel for stream-oriented listening sockets.
 *面向流监听socket可选择通道。
 *  A server-socket channel is created by invoking the {@link #open() open}
 * method of this class.  It is not possible to create a channel for an arbitrary,
 * pre-existing {@link ServerSocket}. A newly-created server-socket channel is
 * open but not yet bound.  An attempt to invoke the {@link #accept() accept}
 * method of an unbound server-socket channel will cause a {@link NotYetBoundException}
 * to be thrown. A server-socket channel can be bound by invoking one of the
 * {@link #bind(java.net.SocketAddress,int) bind} methods defined by this class.
 *ServerSocketChannel通过open方法，创建一个ServerSocketChannel通道。如果已经存在一个
ServerSocket，将不会创建ServerSocketChannel。新创建的ServerSocketChannel是没有绑定地址的。
调用没有绑定地址的ServerSocketChannel的accept方法，将会抛出NotYetBoundException。
可以通过bind方法绑定地址。
 * <p> Socket options are configured using the {@link #setOption(SocketOption,Object)
 * setOption} method. Server-socket channels support the following options:
 可用#setOption方法，配置socket选项，ServerSocketChannel支持的选项配置如下：
 * <blockquote>
 * <table border>
 *   <tr>
 *     <th>Option Name</th>
 *     <th>Description</th>
 *   </tr>
 *   <tr>接受缓冲区大小
 *     <td> {@link java.net.StandardSocketOptions#SO_RCVBUF SO_RCVBUF} </td>
//StandardSocketOptions
 *     <td> The size of the socket receive buffer </td>
  public static final SocketOption<Integer> SO_RCVBUF =
        new StdSocketOption<Integer>("SO_RCVBUF", Integer.class);
 *   </tr>
 *   <tr>是否可以重用地址
 *     <td> {@link java.net.StandardSocketOptions#SO_REUSEADDR SO_REUSEADDR} </td>
 *     <td> Re-use address </td>
 //StandardSocketOptions
 public static final SocketOption<Boolean> SO_REUSEADDR =
        new StdSocketOption<Boolean>("SO_REUSEADDR", Boolean.class);
 *   </tr>
 * </table>
 * </blockquote>
 * Additional (implementation specific) options may also be supported.
 *
 * <p> Server-socket channels are safe for use by multiple concurrent threads.
 ServerSocketChannel是线程安全的
 * 

 *
 * @author Mark Reinhold
 * @author JSR-51 Expert Group
 * @since 1.4
 */

public abstract class ServerSocketChannel
    extends AbstractSelectableChannel
    implements NetworkChannel
{

    /**
     * Initializes a new instance of this class.
     */
    protected ServerSocketChannel(SelectorProvider provider) {
        super(provider);
    }

    /**
     * Opens a server-socket channel.
     *打开一个ServerSocketChannel
     *  The new channel is created by invoking the {@link
     * java.nio.channels.spi.SelectorProvider#openServerSocketChannel
     * openServerSocketChannel} method of the system-wide default {@link
     * java.nio.channels.spi.SelectorProvider} object.
     *通过系统默认的SelectorProvider实现创建一个ServerSocketChannel
     * <p> The new channel's socket is initially unbound; it must be bound to a
     * specific address via one of its socket's {@link
     * java.net.ServerSocket#bind(SocketAddress) bind} methods before
     * connections can be accepted.  

     *新创建的ServerSocketChannel初始是没有绑定的，在接受连接之前必须绑定一个SocketAddress
     * @return  A new socket channel
     *
     * @throws  IOException
     *          If an I/O error occurs
     */
    public static ServerSocketChannel open() throws IOException {
        return SelectorProvider.provider().openServerSocketChannel();
    }

    /**
     * Returns an operation set identifying this channel's supported
     * operations.
     *返回通道支持的操作事件集
     *  Server-socket channels only support the accepting of new
     * connections, so this method returns {@link SelectionKey#OP_ACCEPT}.
      ServerSocketChannel只支持接受连接操作事件
     * 

     *
     * @return  The valid-operation set
     */
    public final int validOps() {
        return SelectionKey.OP_ACCEPT;
    }


    // -- ServerSocket-specific operations --

    /**
     * Binds the channel's socket to a local address and configures the socket
     * to listen for connections.
     *绑定ServerSocketChannel到本地的socket地址，并配置socket监听连接，
     具体实现看bind(SocketAddress local, int backlog)方法
     *  An invocation of this method is equivalent to the following:
     * <blockquote><pre>
     * bind(local, 0);
     * </pre></blockquote>
     *
     * @param   local
     *          The local address to bind the socket, or {@code null} to bind
     *          to an automatically assigned socket address
     *
     * @return  This channel
     *
     * @throws  AlreadyBoundException               {@inheritDoc}
     * @throws  UnsupportedAddressTypeException     {@inheritDoc}
     * @throws  ClosedChannelException              {@inheritDoc}
     * @throws  IOException                         {@inheritDoc}
     * @throws  SecurityException
     *          If a security manager has been installed and its {@link
     *          SecurityManager#checkListen checkListen} method denies the
     *          operation
     *
     * @since 1.7
     */
    public final ServerSocketChannel bind(SocketAddress local)
        throws IOException
    {   
        //委托给bind(SocketAddress local, int backlog)
        return bind(local, 0);
    }

    /**
     * Binds the channel's socket to a local address and configures the socket to
     * listen for connections.
     *绑定ServerSocketChannel到本地的socket地址，并配置socket监听连接
     * <p> 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.
     *这个方法用于建立socket与本地socket地址的联系。只要联系建立，在通道关闭之前，socket
     能绑定着地址。
     * <p> The {@code backlog} parameter is the maximum number of pending
     * connections on the socket. Its exact semantics are implementation specific.
     * In particular, an implementation may impose a maximum length or may choose
     * to ignore the parameter altogther. If the {@code backlog} parameter has
     * the value {@code 0}, or a negative value, then an implementation specific
     * default is used.
     *backlog参数是socket运行接受的最大连接数。具体的含义要根据具体的实现，有的是最大连接数，
     有的可能忽略这个参数。如果参数为0或者一个负数，将会使用默认的实现机制

     * @param   local 本地socket地址
     *          The address to bind the socket, or {@code null} to bind to an
     *          automatically assigned socket address
     * @param   backlog 最大连接数
     *          The maximum number of pending connections
     *
     * @return  This channel
     *
     * @throws  AlreadyBoundException 地址已经绑定
     *          If the socket is already bound
     * @throws  UnsupportedAddressTypeException 地址不支持
     *          If the type of the given address is not supported
     * @throws  ClosedChannelException 通道关闭
     *          If this channel is closed
     * @throws  IOException  IO操作异常
     *          If some other I/O error occurs
     * @throws  SecurityException
     *          If a security manager has been installed and its {@link
     *          SecurityManager#checkListen checkListen} method denies the
     *          operation
     *
     * @since 1.7
     */
    public abstract ServerSocketChannel bind(SocketAddress local, int backlog)
        throws IOException;

    /**
     * @throws  UnsupportedOperationException           {@inheritDoc}
     * @throws  IllegalArgumentException                {@inheritDoc}
     * @throws  ClosedChannelException                  {@inheritDoc}
     * @throws  IOException                             {@inheritDoc}
     *设置选项
     * @since 1.7
     */
    public abstract <T> ServerSocketChannel setOption(SocketOption<T> name, T value)
        throws IOException;

    /**
     * Retrieves a server socket associated with this channel.
     *返回与通道关联的ServerSocket
     * <p> The returned object will not declare any public methods that are not
     * declared in the {@link java.net.ServerSocket} class.  

     *
     * @return  A server socket associated with this channel
     */
    public abstract ServerSocket socket();

    /**
     * Accepts a connection made to this channel's socket.
     * 接受一个连接到通道socket的请求。
     *  If this channel is in non-blocking mode then this method will
     * immediately return <tt>null</tt> if there are no pending connections.
     * Otherwise it will block indefinitely until a new connection is available
     * or an I/O error occurs.
     *如果通道是非阻塞模式，，如果连接已经达到最大数量，则立即返回null；
     否则不确定地阻塞直到一个新的连接可用或者IO错误发生
     * <p> The socket channel returned by this method, if any, will be in
     * blocking mode regardless of the blocking mode of this channel.
     * 如果通道是阻塞模式，则将返回一个SocketChannle，并忽略阻塞模式
     * <p> This method performs exactly the same security checks as the {@link
     * java.net.ServerSocket#accept accept} method of the {@link
     * java.net.ServerSocket} class.  That is, if a security manager has been
     * installed then for each new connection this method verifies that the
     * address and port number of the connection's remote endpoint are
     * permitted by the security manager's {@link
     * java.lang.SecurityManager#checkAccept checkAccept} method.  

     *此方执行精确的安全检查
     * @return  The socket channel for the new connection,
     *          or <tt>null</tt> if this channel is in non-blocking mode
     *          and no connection is available to be accepted
     *
     * @throws  ClosedChannelException
     *          If this channel is closed
     *
     * @throws  AsynchronousCloseException
     *          If another thread closes this channel
     *          while the accept operation is in progress
     *
     * @throws  ClosedByInterruptException 如果其他线程中断当前线程，则关闭通道，设置当前线程的中断位。
     *          If another thread interrupts the current thread
     *          while the accept operation is in progress, thereby
     *          closing the channel and setting the current thread's
     *          interrupt status
     *
     * @throws  NotYetBoundException 地址没有绑定
     *          If this channel's socket has not yet been bound
     *
     * @throws  SecurityException 安全异常
     *          If a security manager has been installed
     *          and it does not permit access to the remote endpoint
     *          of the new connection
     *
     * @throws  IOException IO操作异常
     *          If some other I/O error occurs
     */
    public abstract SocketChannel accept() throws IOException;

}

从上面可以看出ServerSocketChannel主要是绑定socket地址，监听Socket连接。