SelectionKey

1：selectionKey.channel()方法返回的  channel是ServerSocketChannel還是SocketChannel是由前邊注冊這個key時是注冊channel確定的。

 

2：基本處理流程

服務器端先注冊接收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();

    

    處理key

 

 

}

 

3：一般ServerSocketChannel只注冊accept事件，對於read和write事件是注冊到accept的SocketChannel中的

 

public class NIOServer {

     /*標識數字*/
     private   int flag = 0;
     /*緩沖區大小*/
     private   int BLOCK = 4096;
     /*接受數據緩沖區*/
     private  ByteBuffer sendbuffer = ByteBuffer.allocate(BLOCK);
     /*發送數據緩沖區*/
     private  ByteBuffer receivebuffer = ByteBuffer.allocate(BLOCK);
     private  Selector selector;

     public NIOServer( int port) throws IOException {
         // 打開服務器套接字通道
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
         // 服務器配置為非阻塞
        serverSocketChannel.configureBlocking(false);
         // 檢索與此通道關聯的服務器套接字
        ServerSocket serverSocket = serverSocketChannel.socket();
         // 進行服務的綁定
        serverSocket.bind( new InetSocketAddress(port));
         // 通過open()方法找到Selector
        selector = Selector.open();
         // 注冊到selector，等待連接
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
        System.out.println( "Server Start----8888:");
    }


     // 監聽
     private void listen() throws IOException {
         while (true) {
             // 選擇一組鍵，並且相應的通道已經打開
            selector.select();
             // 返回此選擇器的已選擇鍵集。
            Set <SelectionKey > selectionKeys = selector.selectedKeys();
            Iterator <SelectionKey > iterator = selectionKeys.iterator();
             while (iterator.hasNext()) {
                SelectionKey selectionKey = iterator.next();
                iterator.remove();
                handleKey(selectionKey);
            }
        }
    }

     // 處理請求
     private void handleKey(SelectionKey selectionKey) throws IOException {
         // 接受請求
        ServerSocketChannel server = null;
        SocketChannel client = null;
        String receiveText;
        String sendText;
         int count = 0;
         // 測試此鍵的通道是否已准備好接受新的套接字連接。
         if (selectionKey.isAcceptable()) {
             // 返回為之創建此鍵的通道。
            server = (ServerSocketChannel) selectionKey.channel();
             // 接受到此通道套接字的連接。
             // 此方法返回的套接字通道（如果有）將處於阻塞模式。
            client = server.accept();
             // 配置為非阻塞
            client.configureBlocking(false);
             // 注冊到selector，等待連接
            client.register(selector, SelectionKey.OP_READ);
        } else if (selectionKey.isReadable()) {
             // 返回為之創建此鍵的通道。
            client = (SocketChannel) selectionKey.channel();
             //將緩沖區清空以備下次讀取
            receivebuffer.clear();
             //讀取服務器發送來的數據到緩沖區中
            count = client.read(receivebuffer);
             if (count > 0) {
                receiveText = new String( receivebuffer.array(), 0,count);
                System.out.println( "服務器端接受客戶端數據--:" +receiveText);
                client.register(selector, SelectionKey.OP_WRITE);
            }
        } else if (selectionKey.isWritable()) {
             //將緩沖區清空以備下次寫入
            sendbuffer.clear();
             // 返回為之創建此鍵的通道。
            client = (SocketChannel) selectionKey.channel();
            sendText = "message from server--" + flag ++;
             //向緩沖區中輸入數據
            sendbuffer.put(sendText.getBytes());
              //將緩沖區各標志復位,因為向里面put了數據標志被改變要想從中讀取數據發向服務器,就要復位
            sendbuffer.flip();
             //輸出到通道
            client.write(sendbuffer);
            System.out.println( "服務器端向客戶端發送數據--：" +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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