SelectionKey

1：selectionKey.channel()方法返回的  channel是ServerSocketChannel还是SocketChannel是由前边注册这个key时是注册channel确定的。

 

2：基本处理流程

服务器端先注册接收Key

serverSocketChannel.register(selector,SelectionKey.OP_ACCEPT)

 

while(true){

selector.select();

Set<SelectionKey> keys=selector.selectedKeys();

Iterator it=keys.iterator();

 

while(it.hasNext()){

    SelectionKey key=it.next();

    it.remove();

    

    处理key

 

 

}

 

3：一般ServerSocketChannel只注册accept事件，对于read和write事件是注册到accept的SocketChannel中的

 

public class NIOServer {

     /*标识数字*/
     private   int flag = 0;
     /*缓冲区大小*/
     private   int BLOCK = 4096;
     /*接受数据缓冲区*/
     private  ByteBuffer sendbuffer = ByteBuffer.allocate(BLOCK);
     /*发送数据缓冲区*/
     private  ByteBuffer receivebuffer = ByteBuffer.allocate(BLOCK);
     private  Selector selector;

     public NIOServer( int port) throws IOException {
         // 打开服务器套接字通道
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
         // 服务器配置为非阻塞
        serverSocketChannel.configureBlocking(false);
         // 检索与此通道关联的服务器套接字
        ServerSocket serverSocket = serverSocketChannel.socket();
         // 进行服务的绑定
        serverSocket.bind( new InetSocketAddress(port));
         // 通过open()方法找到Selector
        selector = Selector.open();
         // 注册到selector，等待连接
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
        System.out.println( "Server Start----8888:");
    }


     // 监听
     private void listen() throws IOException {
         while (true) {
             // 选择一组键，并且相应的通道已经打开
            selector.select();
             // 返回此选择器的已选择键集。
            Set <SelectionKey > selectionKeys = selector.selectedKeys();
            Iterator <SelectionKey > iterator = selectionKeys.iterator();
             while (iterator.hasNext()) {
                SelectionKey selectionKey = iterator.next();
                iterator.remove();
                handleKey(selectionKey);
            }
        }
    }

     // 处理请求
     private void handleKey(SelectionKey selectionKey) throws IOException {
         // 接受请求
        ServerSocketChannel server = null;
        SocketChannel client = null;
        String receiveText;
        String sendText;
         int count = 0;
         // 测试此键的通道是否已准备好接受新的套接字连接。
         if (selectionKey.isAcceptable()) {
             // 返回为之创建此键的通道。
            server = (ServerSocketChannel) selectionKey.channel();
             // 接受到此通道套接字的连接。
             // 此方法返回的套接字通道（如果有）将处于阻塞模式。
            client = server.accept();
             // 配置为非阻塞
            client.configureBlocking(false);
             // 注册到selector，等待连接
            client.register(selector, SelectionKey.OP_READ);
        } else if (selectionKey.isReadable()) {
             // 返回为之创建此键的通道。
            client = (SocketChannel) selectionKey.channel();
             //将缓冲区清空以备下次读取
            receivebuffer.clear();
             //读取服务器发送来的数据到缓冲区中
            count = client.read(receivebuffer);
             if (count > 0) {
                receiveText = new String( receivebuffer.array(), 0,count);
                System.out.println( "服务器端接受客户端数据--:" +receiveText);
                client.register(selector, SelectionKey.OP_WRITE);
            }
        } else if (selectionKey.isWritable()) {
             //将缓冲区清空以备下次写入
            sendbuffer.clear();
             // 返回为之创建此键的通道。
            client = (SocketChannel) selectionKey.channel();
            sendText = "message from server--" + flag ++;
             //向缓冲区中输入数据
            sendbuffer.put(sendText.getBytes());
              //将缓冲区各标志复位,因为向里面put了数据标志被改变要想从中读取数据发向服务器,就要复位
            sendbuffer.flip();
             //输出到通道
            client.write(sendbuffer);
            System.out.println( "服务器端向客户端发送数据--：" +sendText);
            client.register(selector, SelectionKey.OP_READ);
        }
    }

     /**
     * @param args
     * @throws IOException
     */
     public static void main(String[] args) throws IOException {
         // TODO Auto-generated method stub
         int port = 8888;
        NIOServer server = new NIOServer(port);
        server.listen();
    }
}

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