阅读本教程后：http://rox-xmlrpc.sourceforge.net/niotut/（它是关于编写非阻塞服务器和客户端，我读NIO部分，滑雪SSL部分），现在我正在尝试重写我自己的客户端，但我是在尝试编辑客户端代码时陷入了问题。
首先，我想让您看到本教程的客户端代码，它包含2个文件：
RspHandler.java： http://rox-xmlrpc.sourceforge.net/niotut/src/RspHandler.java
NIOClient.java： http://rox-xmlrpc.sourceforge.net/niotut/src/NioClient.java
但我在main函数中编辑了一下NIOClient.java以解释我的问题，如下所示：
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();
}
}
}
我编辑的客户端只是做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的消息。当然，上面的代码效果很好。它发送2条消息然后正确接收它们。
但是我在上面的客户端中不想要的是：send函数调用此代码：
// Start a new connection SocketChannel socket = this.initiateConnection();
这意味着每个区分消息都会与每个区分新的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();
}
}
}
但是在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这个问题
任何人都知道anwser？
感谢您阅读我的长篇问题。
答案 0 :(得分：4)
你是从错误的地方开始的。该文章存在许多问题。所有挂起 - 更改队列的东西都是一个巨大的，不必要的复杂功能。只需wakeup()选择器，如果你需要注册/取消注册另一个线程（虽然为什么你需要这样做对我来说是一个完全的谜），你可以随时更改interestOps即使他正在推广不同实施的FUD，也会实现完美的可靠性。
这篇文章还有其他几个问题，表明作者并不真正知道他在说什么。 IOException并不一定意味着“远程强行关闭连接”。他的finishConnection()方法忽略了返回值，如果为false，则表示连接仍处于未决状态，因此它会过早地将通道注册到OP_CONNECT阶段之外。关闭频道会取消该密钥，因此紧接cancel()次呼叫之前或之后的所有close()次呼叫都是多余的并且可以被删除（尽管有些地方他取消而不关闭，这也是错误的地方发生）。
此外：
无处在刚引入的两种方法中我们请求了 在套接字通道的选择键上设置OP_CONNECT标志。要是我们 这样做我们会覆盖OP_CONNECT标志并且永远不会完成 连接。如果我们将它们合并在一起，那么我们就冒着尝试写作的风险 一个未连接的渠道（或至少不得不处理该案件）“
这只是完整的A级废话。将OP_CONNECT设置两次，或者“将它们组合”，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可以清除它。
数据已经排队（或者我们不会建立数据 首先是连接。）
一种奇怪而无法解释的假设。
如果你在Oracle论坛迁移后仍能找到它，那么我会很好地看看他引用的“驯服NIO马戏团”主题，而不是那个相当可疑的混乱。免责声明：我写了一些内容。