我正在学习Java nio选择器.在我的理解中,我认为使用选择器的步骤是首先注册我的兴趣操作,然后我可以检查准备好的设置,最后可以进行与我的兴趣操作相对应的操作.我不知道为什么在这段代码中,写入过程会在if(key.isReadable()){…}块中发生,但是如果if(key.isWritable){…}不会发生,为什么写入操作不起作用注册?
Iterator keys = sel.selectedKeys().iterator();
while (keys.hasNext()) {
SelectionKey key = (SelectionKey)keys.next();
if (!key.isValid())
continue;
if (key.isAcceptable()) {
// increase the counter
connection++;
// remove accept request
keys.remove();
// ACCEPT: get the server channel
ServerSocketChannel ssc =
(ServerSocketChannel) key.channel();
// init a socket for a client
SocketChannel nsc = ssc.accept();
nsc.configureBlocking(false);
// register the socket for READ
nsc.register(sel, SelectionKey.OP_READ);
}
}
while (count < COUNT_MAX + NUM_CHILD - 1) {
sel.select();
// Get all pending events and iterate
Iterator keys = sel.selectedKeys().iterator();
while ( keys.hasNext() ) {
SelectionKey key = (SelectionKey)keys.next();
keys.remove();
if (!key.isValid())
continue;
if (key.isReadable()) {
// READ: get the channel
SocketChannel nsc = (SocketChannel) key.channel();
// clear buffer for reading
readBuffer.clear();
int nBytes = nsc.read(readBuffer);
if (nBytes == -1) {// Check if the client closed the socket
key.channel().close();
key.cancel();
continue;
}
// Read a message
DataInputStream ist = new DataInputStream (
new ByteArrayInputStream(readBuffer.array()));
String msg = ist.readUTF();
System.out.print(msg + "\n");
// Clear the write buffer
writeBuffer.clear();
// Write the counter value on the buffer
count++;
if (count < COUNT_MAX)
writeBuffer.putInt(count);
else
writeBuffer.putInt(-1);
// flip the buffer and write on the channel
writeBuffer.flip();
// Reply to a client
nsc.write(writeBuffer);
}
} // while (key)
解决方法:
您不需要在OP_WRITE中注册兴趣,因为通常该通道已准备好进行写入.但是,如果处于非阻塞模式,则WritableChannel可能无法成功写入给定ByteBuffer的所有内容.参见此处的Java文档:
Some types of channels,
depending upon their state, may write only some of the bytes or
possibly none at all. A socket channel in non-blocking mode, for
example, cannot write any more bytes than are free in the socket’s
output buffer.
在这种情况下,您需要在选择器上注册OP_WRITE的兴趣,以便在通道再次准备好写入时得到通知,以便可以完成写入ByteBuffer的操作.
请参阅此处的相关SO question.
标签:nio,java 来源: https://codeday.me/bug/20191029/1957287.html
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