Java NIO 从远程机器读取和写入

Question

我想使用 NIO 向远程计算机发送数据/从远程计算机接收数据。我可以随时发送或接收数据，当我需要发送数据时，我只是发送数据，而不需要来自远程机器的任何查询，并且远程机器定期向我发送数据。我不明白NIO机制。什么在 Selector SelectionKey 上生成并读取或写入事件？是否可以在我这边仅使用一个 ServerSocketChannel 从远程机器读取数据并写入数据？这就是我的理解，但我不知道如何触发写入事件...谢谢您的解释。

我已经做了一些编码，我可以读取来自远程机器的数据，但无法写入。我使用选择器，我不知道如何写入数据。记录的消息“handle write”永远不会被写入，但在wireshark中我可以看到我的数据包。

    public class ServerSelector {

    private static final Logger logger = Logger.getLogger(ServerSelector.class.getName());
    private static final int TIMEOUT = 3000; // Wait timeout (milliseconds)
    private static final int MAXTRIES = 3;
    private final Selector selector;

    public ServerSelector(Controller controller, int... servPorts) throws IOException {
        if (servPorts.length <= 0) {
            throw new IllegalArgumentException("Parameter(s) : <Port>...");
        }
        Handler consolehHandler = new ConsoleHandler();
        consolehHandler.setLevel(Level.INFO);
        logger.addHandler(consolehHandler);

        // Create a selector to multiplex listening sockets and connections
        selector = Selector.open();

        // Create listening socket channel for each port and register selector
        for (int servPort : servPorts) {
            ServerSocketChannel listnChannel = ServerSocketChannel.open();
            listnChannel.socket().bind(new InetSocketAddress(servPort));

            listnChannel.configureBlocking(false); // must be nonblocking to register
            // Register selector with channel.  The returned key is ignored
            listnChannel.register(selector, SelectionKey.OP_ACCEPT);
        }

        // Create a handler that will implement the protocol
        IOProtocol protocol = new IOProtocol();

        int tries = 0;
        // Run forever, processing available I/O operations
        while (tries < MAXTRIES) {
            // Wait for some channel to be ready (or timeout)
            if (selector.select(TIMEOUT) == 0) { // returns # of ready chans
                System.out.println(".");
                tries += 1;
                continue;
            }

            // Get iterator on set of keys with I/O to process
            Iterator<SelectionKey> keyIter = selector.selectedKeys().iterator();
            while (keyIter.hasNext()) {
                SelectionKey key = keyIter.next(); // Key is a bit mask
                // Server socket channel has pending connection requests?
                if (key.isAcceptable()) {
                    logger.log(Level.INFO, "handle accept");
                    protocol.handleAccept(key, controller);
                }

                // Client socket channel has pending data?
                if (key.isReadable()) {
                    logger.log(Level.INFO, "handle read");
                    protocol.handleRead(key);
                }

                // Client socket channel is available for writing and
                // key is valid (i.e., channel not closed) ?
                if (key.isValid() && key.isWritable()) {
                    logger.log(Level.INFO, "handle write");
                    protocol.handleWrite(key);
                }
                keyIter.remove(); // remove from set of selected keys
                tries = 0;
            }
        }
    }
}

协议(protocol)

    public class IOProtocol implements Protocol {

    private static final Logger logger = Logger.getLogger(IOProtocol.class.getName());

    IOProtocol() {
        Handler consolehHandler = new ConsoleHandler();
        consolehHandler.setLevel(Level.INFO);
        logger.addHandler(consolehHandler);
    }

    /**
     *
     * @param key
     * @throws IOException
     */
    @Override
    public void handleAccept(SelectionKey key, Controller controller) throws IOException {
        SocketChannel clntChan = ((ServerSocketChannel) key.channel()).accept();
        clntChan.configureBlocking(false); // Must be nonblocking to register
        controller.setCommChannel(clntChan);
        // Register the selector with new channel for read and attach byte buffer
        SelectionKey socketKey = clntChan.register(key.selector(), SelectionKey.OP_READ | SelectionKey.OP_WRITE, controller);
    }

    /**
     * Client socket channel has pending data
     *
     * @param key
     * @throws IOException
     */
    @Override
    public void handleRead(SelectionKey key) throws IOException {
        Controller ctrller = (Controller)key.attachment();
        try {
            ctrller.readData();
        } catch (CommandUnknownException ex) {
            logger.log(Level.SEVERE, null, ex);
        }
        key.interestOps(SelectionKey.OP_READ | SelectionKey.OP_WRITE);
    }

    /**
     * Channel is available for writing, and key is valid (i.e., client channel
     * not closed).
     *
     * @param key
     * @throws IOException
     */
    @Override
    public void handleWrite(SelectionKey key) throws IOException {

        Controller ctrl = (Controller)key.attachment();
        ctrl.writePendingData();
        if (!buf.hasRemaining()) { // Buffer completely written ?
            // Nothing left, so no longer interested in writes
            key.interestOps(SelectionKey.OP_READ);
        }
    buf.compact();
    }
}

Controller

    /**
     * Fill buffer with data.
     * @param msg The data to be sent
     * @throws IOException 
     */
    private void writeData(AbstractMsg msg) throws IOException {
//        
        writeBuffer = ByteBuffer.allocate(msg.getSize() + 4);
        writeBuffer.putInt(msg.getSize());
        msg.writeHeader(writeBuffer);
        msg.writeData(writeBuffer);
        logger.log(Level.INFO, "Write data - message size : {0}", new Object[]{msg.getSize()});
        logger.log(Level.INFO, "Write data - message : {0}", new Object[]{msg});
    }

    /**
     * Write to the SocketChannel
     * @throws IOException 
     */
    public void writePendingData() throws IOException {
        commChannel.write(writeBuffer);
    }

Answer 1

ServerSocketChannel 用于建立连接，但不发送数据。每个连接都需要一个 ServerSocketChannel 和一个 SocketChannel。

使用SocketChannel读写示例:

ByteBuffer buf = ByteBuffer.allocate(48);
int bytesRead = socketChannel.read(buf);

你的程序将在第二行 hibernate ，直到数据到来。您需要将此代码置于无限循环中并在后台线程中运行它。当数据到来时，您可以从该线程处理它，然后等待另一个数据到来。

ByteBuffer buf = ByteBuffer.allocate(48);
buf.clear();
buf.put("Hello!".getBytes());

buf.flip();

while(buf.hasRemaining()) {
    channel.write(buf);
}

没有阻塞方法，因此如果您发送小字节缓冲区，您可以从主线程调用它。

Source

添加:不要在新连接上设置 OP_WRITE 键。仅OP_READ。当您想要写入一些数据时，您需要通知选择器您想要发送一些内容并在事件循环中发送它。好的解决方案是创建一个输出消息的队列。然后按照以下步骤操作:

• 将数据添加到队列
• 将 OP_WRITE 设置为 channel key
• 在 while (keyIter.hasNext()) 循环中，您将拥有可写 key ，从队列中写入所有数据并删除OP_WRITE key .

我很难理解你的代码，但我想你会找出问题所在。另外，如果您只想有一个连接，则无需使用Selector。您绑定(bind)了几个 ServerSocketChannels，这很奇怪。