仅通过一个 SocketChannel 发送多条消息

读完本教程后：http://rox-xmlrpc.sourceforge.net/niotut/ http://rox-xmlrpc.sourceforge.net/niotut/（这是关于编写非阻塞服务器和客户端，我阅读了NIO部分，跳过了SSL部分），现在我正在尝试重写我自己的客户端，但是在尝试编辑客户端代码时遇到了问题。

首先，我想让你看一下教程的客户端代码，它包含2个文件：

• RspHandler.java：http://rox-xmlrpc.sourceforge.net/niotut/src/RspHandler.java http://rox-xmlrpc.sourceforge.net/niotut/src/RspHandler.java

• NIOClient.java：http://rox-xmlrpc.sourceforge.net/niotut/src/NioClient.java http://rox-xmlrpc.sourceforge.net/niotut/src/NioClient.java

但我编辑了 NIOClient.java 一点main函数解释我的问题如下：

import java.io.IOException;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.nio.channels.spi.SelectorProvider;
import java.util.*;

public class NIOClient implements Runnable {
// The host:port combination to connect to
private InetAddress hostAddress;
private int port;

// The selector we'll be monitoring
private Selector selector;

// The buffer into which we'll read data when it's available
private ByteBuffer readBuffer = ByteBuffer.allocate(8192);

// A list of PendingChange instances
private List pendingChanges = new LinkedList();

// Maps a SocketChannel to a list of ByteBuffer instances
private Map pendingData = new HashMap();

// Maps a SocketChannel to a RspHandler
private Map rspHandlers = Collections.synchronizedMap(new HashMap());

public NIOClient(InetAddress hostAddress, int port) throws IOException {
    this.hostAddress = hostAddress;
    this.port = port;
    this.selector = this.initSelector();
}

public void send(byte[] data, RspHandler handler) throws IOException {
    // Start a new connection
    SocketChannel socket = this.initiateConnection();

    // Register the response handler
    this.rspHandlers.put(socket, handler);

    // And queue the data we want written
    synchronized (this.pendingData) {
        List queue = (List) this.pendingData.get(socket);
        if (queue == null) {
            queue = new ArrayList();
            this.pendingData.put(socket, queue);
        }
        queue.add(ByteBuffer.wrap(data));
    }

    // Finally, wake up our selecting thread so it can make the required changes
    this.selector.wakeup();
}

public void run() {
    while (true) {
        try {
            // Process any pending changes
            synchronized (this.pendingChanges) {
                Iterator changes = this.pendingChanges.iterator();
                while (changes.hasNext()) {
                    ChangeRequest change = (ChangeRequest) changes.next();
                    switch (change.type) {
                    case ChangeRequest.CHANGEOPS:
                        SelectionKey key = change.socket.keyFor(this.selector);
                        key.interestOps(change.ops);
                        break;
                    case ChangeRequest.REGISTER:
                        change.socket.register(this.selector, change.ops);
                        break;
                    }
                }
                this.pendingChanges.clear();
            }

            // Wait for an event one of the registered channels
            this.selector.select();

            // Iterate over the set of keys for which events are available
            Iterator selectedKeys = this.selector.selectedKeys().iterator();
            while (selectedKeys.hasNext()) {
                SelectionKey key = (SelectionKey) selectedKeys.next();
                selectedKeys.remove();

                if (!key.isValid()) {
                    continue;
                }

                // Check what event is available and deal with it
                if (key.isConnectable()) {
                    this.finishConnection(key);
                } else if (key.isReadable()) {
                    this.read(key);
                } else if (key.isWritable()) {
                    this.write(key);
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

private void read(SelectionKey key) throws IOException {
    SocketChannel socketChannel = (SocketChannel) key.channel();

    // Clear out our read buffer so it's ready for new data
    this.readBuffer.clear();

    // Attempt to read off the channel
    int numRead;
    try {
        numRead = socketChannel.read(this.readBuffer);
    } catch (IOException e) {
        // The remote forcibly closed the connection, cancel
        // the selection key and close the channel.
        key.cancel();
        socketChannel.close();
        return;
    }

    if (numRead == -1) {
        // Remote entity shut the socket down cleanly. Do the
        // same from our end and cancel the channel.
        key.channel().close();
        key.cancel();
        return;
    }

    // Handle the response
    this.handleResponse(socketChannel, this.readBuffer.array(), numRead);
}

private void handleResponse(SocketChannel socketChannel, byte[] data, int numRead) throws IOException {
    // Make a correctly sized copy of the data before handing it
    // to the client
    byte[] rspData = new byte[numRead];
    System.arraycopy(data, 0, rspData, 0, numRead);

    // Look up the handler for this channel
    RspHandler handler = (RspHandler) this.rspHandlers.get(socketChannel);

    // And pass the response to it
    if (handler.handleResponse(rspData)) {
        // The handler has seen enough, close the connection
        socketChannel.close();
        socketChannel.keyFor(this.selector).cancel();
    }
}

private void write(SelectionKey key) throws IOException {
    SocketChannel socketChannel = (SocketChannel) key.channel();

    synchronized (this.pendingData) {
        List queue = (List) this.pendingData.get(socketChannel);

        // Write until there's not more data ...
        while (!queue.isEmpty()) {
            ByteBuffer buf = (ByteBuffer) queue.get(0);
            socketChannel.write(buf);
            if (buf.remaining() > 0) {
                // ... or the socket's buffer fills up
                break;
            }
            queue.remove(0);
        }

        if (queue.isEmpty()) {
            // We wrote away all data, so we're no longer interested
            // in writing on this socket. Switch back to waiting for
            // data.
            key.interestOps(SelectionKey.OP_READ);
        }
    }
}

private void finishConnection(SelectionKey key) throws IOException {
    SocketChannel socketChannel = (SocketChannel) key.channel();

    // Finish the connection. If the connection operation failed
    // this will raise an IOException.
    try {
        socketChannel.finishConnect();
    } catch (IOException e) {
        // Cancel the channel's registration with our selector
        System.out.println(e);
        key.cancel();
        return;
    }

    // Register an interest in writing on this channel
    key.interestOps(SelectionKey.OP_WRITE);
}

private SocketChannel initiateConnection() throws IOException {
    // Create a non-blocking socket channel
    SocketChannel socketChannel = SocketChannel.open();
    socketChannel.configureBlocking(false);

    // Kick off connection establishment
    socketChannel.connect(new InetSocketAddress(this.hostAddress, this.port));

    // Queue a channel registration since the caller is not the 
    // selecting thread. As part of the registration we'll register
    // an interest in connection events. These are raised when a channel
    // is ready to complete connection establishment.
    synchronized(this.pendingChanges) {
        this.pendingChanges.add(new ChangeRequest(socketChannel, ChangeRequest.REGISTER, SelectionKey.OP_CONNECT));
    }

    return socketChannel;
}

private Selector initSelector() throws IOException {
    // Create a new selector
    return SelectorProvider.provider().openSelector();
}

public static void main(String[] args) {
    try {
        NIOClient client = new NIOClient(
                InetAddress.getByName("127.0.0.1"), 9090);
        Thread t = new Thread(client);
        t.setDaemon(true);
        t.start();

        // 1st
        client.send("hehe|||".getBytes());
        System.out.println("SEND: " + "hehe|||");
        handler.waitForResponse();

        System.out.println("------------");

        // 2nd
        client.send(("hehe|||" + " 2").getBytes());
        System.out.println("SEND: " + "hehe|||" + " 2");
        handler.waitForResponse();

    } catch (Exception e) {
        e.printStackTrace();
    }
}
}

我编辑的客户端只做了一件简单的事情，就是向服务器发送消息，然后从服务器接收回显消息。当然，上面的代码运行良好。它发送了 2 条消息，然后正确地收到了它们。

但我不希望在上述客户端中出现的是：send函数调用此代码：

    // Start a new connection
    SocketChannel socket = this.initiateConnection();

这意味着每一个有区别的消息都将与每个有区别的新SocketChannel相对应，但现在我只想使用一个SocketChannel来发送许多消息，所以我像下面的代码一样更改客户端：

import java.io.IOException;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.nio.channels.spi.SelectorProvider;
import java.util.*;

public class MyClient implements Runnable {
// The host:port combination to connect to
private InetAddress hostAddress;
private int port;

// The selector we'll be monitoring
private Selector selector;

// The buffer into which we'll read data when it's available
private ByteBuffer readBuffer = ByteBuffer.allocate(8);

// A list of PendingChange instances
private List pendingChanges = new LinkedList();

// Maps a SocketChannel to a list of ByteBuffer instances
private Map pendingData = new HashMap();

// Maps a SocketChannel to a RspHandler
private Map rspHandlers = Collections.synchronizedMap(new HashMap());


private SocketChannel socket;
private static MyResponseHandler handler;

public MyClient(InetAddress hostAddress, int port) throws IOException {
    this.hostAddress = hostAddress;
    this.port = port;
    this.selector = this.initSelector();

    // Start a new connection
    socket = this.initiateConnection();

    handler = new MyResponseHandler();
    // Register the response handler
    this.rspHandlers.put(socket, handler);      
}

public void send(byte[] data) throws IOException {

    // And queue the data we want written
    synchronized (this.pendingData) {
        List queue = (List) this.pendingData.get(socket);
        if (queue == null) {
            queue = new ArrayList();
            this.pendingData.put(socket, queue);
        }
        queue.add(ByteBuffer.wrap(data));
    }

    // Finally, wake up our selecting thread so it can make the required changes
    this.selector.wakeup();
}

public void run() {
    while (true) {
        try {
            // Process any pending changes
            synchronized (this.pendingChanges) {
                Iterator changes = this.pendingChanges.iterator();
                while (changes.hasNext()) {
                    ChangeRequest change = (ChangeRequest) changes.next();
                    switch (change.type) {
                    case ChangeRequest.CHANGEOPS:
                        SelectionKey key = change.socket.keyFor(this.selector);
                        key.interestOps(change.ops);
                        break;
                    case ChangeRequest.REGISTER:
                        change.socket.register(this.selector, change.ops);
                        break;
                    }
                }
                this.pendingChanges.clear();
            }

            // Wait for an event one of the registered channels
            this.selector.select();

            // Iterate over the set of keys for which events are available
            Iterator selectedKeys = this.selector.selectedKeys().iterator();
            while (selectedKeys.hasNext()) {
                SelectionKey key = (SelectionKey) selectedKeys.next();
                selectedKeys.remove();

                if (!key.isValid()) {
                    continue;
                }

                // Check what event is available and deal with it
                if (key.isConnectable()) {
                    this.finishConnection(key);
                } else if (key.isReadable()) {
                    this.read(key);
                } else if (key.isWritable()) {
                    this.write(key);
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

private void read(SelectionKey key) throws IOException {
    SocketChannel socketChannel = (SocketChannel) key.channel();

    // Clear out our read buffer so it's ready for new data
    this.readBuffer.clear();

    // Attempt to read off the channel
    int numRead;
    try {
        numRead = socketChannel.read(this.readBuffer);
    } catch (IOException e) {
        // The remote forcibly closed the connection, cancel
        // the selection key and close the channel.
        key.cancel();
        socketChannel.close();
        return;
    }

    if (numRead == -1) {
        // Remote entity shut the socket down cleanly. Do the
        // same from our end and cancel the channel.
        key.channel().close();
        key.cancel();
        return;
    }

    // Handle the response
    this.handleResponse(socketChannel, this.readBuffer.array(), numRead);
}

private void handleResponse(SocketChannel socketChannel, byte[] data, int numRead) throws IOException {
    // Make a correctly sized copy of the data before handing it
    // to the client
    byte[] rspData = new byte[numRead];
    System.arraycopy(data, 0, rspData, 0, numRead);

    // Look up the handler for this channel
    MyResponseHandler handler = (MyResponseHandler) this.rspHandlers.get(socketChannel);

    // And pass the response to it
    if (handler.handleResponse(rspData)) {
        // The handler has seen enough, close the connection
        socketChannel.close();
        socketChannel.keyFor(this.selector).cancel();
    }
}

private void write(SelectionKey key) throws IOException {
    SocketChannel socketChannel = (SocketChannel) key.channel();

    synchronized (this.pendingData) {
        List queue = (List) this.pendingData.get(socketChannel);

        // Write until there's not more data ...
        while (!queue.isEmpty()) {
            ByteBuffer buf = (ByteBuffer) queue.remove(0);
            socketChannel.write(buf);

            //-- DEBUG --
            System.out.println("===>>> socketChannel.write: " + new String(buf.array()));

            if (buf.remaining() > 0) {
                // ... or the socket's buffer fills up
                break;
            }
        }

        if (queue.isEmpty()) {
            // We wrote away all data, so we're no longer interested
            // in writing on this socket. Switch back to waiting for
            // data.
            key.interestOps(SelectionKey.OP_READ);
        }
    }
}

private void finishConnection(SelectionKey key) throws IOException {
    SocketChannel socketChannel = (SocketChannel) key.channel();

    // Finish the connection. If the connection operation failed
    // this will raise an IOException.
    try {
        socketChannel.finishConnect();
    } catch (IOException e) {
        // Cancel the channel's registration with our selector
        System.out.println(e);
        key.cancel();
        return;
    }

    // Register an interest in writing on this channel
    key.interestOps(SelectionKey.OP_WRITE);
}

private SocketChannel initiateConnection() throws IOException {
    // Create a non-blocking socket channel
    SocketChannel socketChannel = SocketChannel.open();
    socketChannel.configureBlocking(false);

    // Kick off connection establishment
    socketChannel.connect(new InetSocketAddress(this.hostAddress, this.port));

    // Queue a channel registration since the caller is not the 
    // selecting thread. As part of the registration we'll register
    // an interest in connection events. These are raised when a channel
    // is ready to complete connection establishment.
    synchronized(this.pendingChanges) {
        this.pendingChanges.add(new ChangeRequest(socketChannel, ChangeRequest.REGISTER, SelectionKey.OP_CONNECT));
    }

    return socketChannel;
}

private Selector initSelector() throws IOException {
    // Create a new selector
    return SelectorProvider.provider().openSelector();
}

public static void main(String[] args) {
    try {
        MyClient client = new MyClient(
                InetAddress.getByName("127.0.0.1"), 9090);
        Thread t = new Thread(client);
        t.setDaemon(true);
        t.start();

        // 1st
        client.send("hehe|||".getBytes());
        System.out.println("SEND: " + "hehe|||");
        handler.waitForResponse();

        System.out.println("------------");

        // 2nd
        client.send(("hehe|||" + " 2").getBytes());
        System.out.println("SEND: " + "hehe|||" + " 2");
        handler.waitForResponse();

    } catch (Exception e) {
        e.printStackTrace();
    }
}
}

但是运行上面的客户端后，我只看到第一条消息被发送和接收回来，经过调试，我知道第二条消息没有发送，但我不知道为什么以及如何解决该问题。

有人知道答案吗？

感谢您阅读我很长的问题。

你从错误的地方开始。那篇文章有很多问题。所有这些待更改队列的内容都是一个巨大的、不必要的复杂化。只是wakeup()如果您需要从另一个线程注册/注销选择器（尽管为什么您需要这样做对我来说完全是个谜），并且您可以更改interestOps任何时候都以同样的方式完全可靠，即使他传播的关于不同实现的 FUD 曾经实现过。

这篇文章还有其他几个问题，表明作者并不真正知道自己在说什么。一个IOException并不一定意味着“远程强制关闭连接”。他的finishConnection()方法忽略返回值，如果为 false，则意味着连接仍处于挂起状态，因此它会注册超出OP_CONNECT过早地阶段。关闭通道会取消密钥，因此所有这些cancel()紧接在其之前或之后的调用close()调用是多余的，可以删除（尽管有些地方他取消了而不关闭，这也是错误的地方）。

Further:

在刚刚介绍的两种方法中，我们没有要求 OP_CONNECT 标志设置在套接字通道的选择键上。要是我们 我们会覆盖 OP_CONNECT 标志并且永远不会完成 联系。如果我们把它们结合起来，那么我们就会冒着试图写下去的风险 一个未连接的通道（或者至少必须处理这种情况）”

这完全是A级废话。设置 OP_CONNECT 两次，或者“然后组合它们”，无论这意味着什么，都不可能导致您“永远不会完成连接”或“尝试在未连接的通道上写入”。他似乎认为设置两次就可以清除它。

数据已经排队（否则我们不会建立一个 首先连接）。

一个奇怪且无法解释的假设。

如果您在 Oracle 论坛迁移后仍然可以找到它，我会仔细看看他引用的“驯服 NIO Circus”主题，而不是那种相当可疑的混乱。免责声明：其中一些是我写的。