使用 NIO 库在 Java 中创建一个简单的 ChatServer 让我很痛苦。想知道是否有人可以帮助我。我通过使用 SocketChannel 和 Selector 在单个线程中处理多个客户端来做到这一点。问题是：我能够接受新连接并获取它的数据，但是当我尝试发回数据时，SocketChannel 根本不起作用。在 write() 方法中，它返回一个与我传递给它的数据大小相同的整数，但客户端永远不会收到该数据。奇怪的是，当我关闭服务器应用程序时，客户端会收到数据。就像 socketchannel 维护一个缓冲区，它只有在我关闭应用程序时才会被刷新。
这里有一些更多的细节，给你更多的信息来帮助。我正在处理这段代码中的事件：
private void run() throws IOException {
ServerSocketChannel ssc = ServerSocketChannel.open();
// Set it to non-blocking, so we can use select
ssc.configureBlocking( false );
// Get the Socket connected to this channel, and bind it
// to the listening port
this.serverSocket = ssc.socket();
InetSocketAddress isa = new InetSocketAddress( this.port );
serverSocket.bind( isa );
// Create a new Selector for selecting
this.masterSelector = Selector.open();
// Register the ServerSocketChannel, so we can
// listen for incoming connections
ssc.register( masterSelector, SelectionKey.OP_ACCEPT );
while (true) {
// See if we've had any activity -- either
// an incoming connection, or incoming data on an
// existing connection
int num = masterSelector.select();
// If we don't have any activity, loop around and wait
// again
if (num == 0) {
continue;
}
// Get the keys corresponding to the activity
// that has been detected, and process them
// one by one
Set keys = masterSelector.selectedKeys();
Iterator it = keys.iterator();
while (it.hasNext()) {
// Get a key representing one of bits of I/O
// activity
SelectionKey key = (SelectionKey)it.next();
// What kind of activity is it?
if ((key.readyOps() & SelectionKey.OP_ACCEPT) ==
SelectionKey.OP_ACCEPT) {
// Aceita a conexão
Socket s = serverSocket.accept();
System.out.println( "LOG: Conexao TCP aceita de " + s.getInetAddress() + ":" + s.getPort() );
// Make sure to make it non-blocking, so we can
// use a selector on it.
SocketChannel sc = s.getChannel();
sc.configureBlocking( false );
// Registra a conexao no seletor, apenas para leitura
sc.register( masterSelector, SelectionKey.OP_READ );
} else if ( key.isReadable() ) {
SocketChannel sc = null;
// It's incoming data on a connection, so
// process it
sc = (SocketChannel)key.channel();
// Verifica se a conexão corresponde a um cliente já existente
if((clientsMap.getClient(key)) != null){
boolean closedConnection = !processIncomingClientData(key);
if(closedConnection){
int id = clientsMap.getClient(key);
closeClient(id);
}
} else {
boolean clientAccepted = processIncomingDataFromNewClient(key);
if(!clientAccepted){
// Se o cliente não foi aceito, sua conexão é simplesmente fechada
sc.socket().close();
sc.close();
key.cancel();
}
}
}
}
// We remove the selected keys, because we've dealt
// with them.
keys.clear();
}
}
这段代码只是处理想要连接到聊天的新客户端。因此，客户端与服务器建立 TCP 连接，一旦被接受，它就会按照简单的文本协议向服务器发送数据，通知他的 id 并要求注册到服务器。我在方法 processIncomingDataFromNewClient(key) 中处理这个问题。我还在类似于哈希表的数据结构中保存了客户端及其连接的映射。我这样做是因为我需要从连接中恢复客户端 ID 和来自客户端 ID 的连接。这可以显示在：clientsMap.getClient(key) 中。但问题本身在于方法 processIncomingDataFromNewClient(key)。在那里，我只是读取客户端发送给我的数据，验证它，如果没问题，我向客户端发送一条消息，告知它已连接到聊天服务器。这是一段类似的代码：
private boolean processIncomingDataFromNewClient(SelectionKey key){
SocketChannel sc = (SocketChannel) key.channel();
String connectionOrigin = sc.socket().getInetAddress() + ":" + sc.socket().getPort();
int id = 0; //id of the client
buf.clear();
int bytesRead = 0;
try {
bytesRead = sc.read(buf);
if(bytesRead<=0){
System.out.println("Conexão fechada pelo: " + connectionOrigin);
return false;
}
System.out.println("LOG: " + bytesRead + " bytes lidos de " + connectionOrigin);
String msg = new String(buf.array(),0,bytesRead);
// Do validations with the client sent me here
// gets the client id
}catch (Exception e) {
e.printStackTrace();
System.out.println("LOG: Oops. Cliente não conhece o protocolo. Fechando a conexão: " + connectionOrigin);
System.out.println("LOG: Primeiros 10 caracteres enviados pelo cliente: " + msg);
return false;
}
}
} catch (IOException e) {
System.out.println("LOG: Erro ao ler dados da conexao: " + connectionOrigin);
System.out.println("LOG: "+ e.getLocalizedMessage());
System.out.println("LOG: Fechando a conexão...");
return false;
}
// If it gets to here, the protocol is ok and we can add the client
boolean inserted = clientsMap.addClient(key, id);
if(!inserted){
System.out.println("LOG: Não foi possível adicionar o cliente. Ou ele já está conectado ou já têm clientes demais. Id: " + id);
System.out.println("LOG: Fechando a conexão: " + connectionOrigin);
return false;
}
System.out.println("LOG: Novo cliente conectado! Enviando mesnsagem de confirmação. Id: " + id + " Conexao: " + connectionOrigin);
/* Here is the error */
sendMessage(id, "Servidor pet: connection accepted");
System.out.println("LOG: Novo cliente conectado! Id: " + id + " Conexao: " + connectionOrigin);
return true;
}
最后，方法 sendMessage(SelectionKey key) 如下所示：
private void sendMessage(int destId, String msg) {
Charset charset = Charset.forName("ISO-8859-1");
CharBuffer charBuffer = CharBuffer.wrap(msg, 0, msg.length());
ByteBuffer bf = charset.encode(charBuffer);
//bf.flip();
int bytesSent = 0;
SelectionKey key = clientsMap.getClient(destId);
SocketChannel sc = (SocketChannel) key.channel();
try {
/
int total_bytes_sent = 0;
while(total_bytes_sent < msg.length()){
bytesSent = sc.write(bf);
total_bytes_sent += bytesSent;
}
System.out.println("LOG: Bytes enviados para o cliente " + destId + ": "+ total_bytes_sent + " Tamanho da mensagem: " + msg.length());
} catch (IOException e) {
System.out.println("LOG: Erro ao mandar mensagem para: " + destId);
System.out.println("LOG: " + e.getLocalizedMessage());
}
}
因此，发生的事情是服务器在发送消息时打印如下内容：
LOG: Bytes sent to the client: 28 Size of the message: 28
因此，它告诉它发送了数据，但聊天客户端一直阻塞，在 recv() 方法中等待。因此，数据永远不会到达它。但是，当我关闭服务器应用程序时，所有数据都会出现在客户端中。我想知道为什么。
重要的是要说客户端在 C 和服务器 JAVA 中，并且我在同一台机器上运行，在 windows 下的 virtualbox 中运行 Ubuntu 来宾。我也在 windows 主机和 linuxes 主机下运行，并且不断遇到同样的奇怪问题。
我很抱歉这个问题很长，但我已经在很多地方搜索了答案，找到了很多教程和问题，包括在 StackOverflow 上，但找不到合理的解释。我真的不喜欢这个Java NIO，我也看到很多人抱怨它。我在想，如果我在 C 语言中这样做会容易得多:-D
所以，如果有人可以帮助我，甚至讨论这种行为，那就太好了！:-)
先谢谢大家了
彼得森