NIO的那些事儿
1. 只有非阻塞Channel才能注册，否则会报IllegalBlockingModeException。
2. sk.interestOps(sk.interestOps()& ~SelectionKey.OP_READ);
//处理业务
sk.interestOps(sk.interestOps()| SelectionKey.OP_READ);
sk.interestOps（）操作必须在与register()操作在同一个线程，否则不起作用。这个观点被证明是错的。
package com.guojje.nio;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.ReadableByteChannel;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.channels.spi.SelectorProvider;
import java.util.Iterator;
import java.util.Set;
public class NioServer {
public static void main(String[] args) throws IOException,
InterruptedException {
ServerSocketChannel ssc = ServerSocketChannel.open();
ssc.bind(new InetSocketAddress("0.0.0.0", 8080));
// Thread.currentThread().sleep(100000);
ssc.configureBlocking(false);
Selector selector = SelectorProvider.provider().openSelector();
ssc.register(selector, SelectionKey.OP_ACCEPT);
while (true) {
int readyChannels = selector.select();
System.out.println("ready channels count:" + readyChannels);
if (readyChannels > 0) {
Set<SelectionKey> selectedKeys = selector.selectedKeys();
Iterator<SelectionKey> it = selectedKeys.iterator();
while(it.hasNext()){
SelectionKey sk = it.next();
it.remove();
if((sk.readyOps() & SelectionKey.OP_ACCEPT) != 0){
ServerSocketChannel serverChannel = (ServerSocketChannel)sk.channel();
SocketChannel sc = serverChannel.accept();
System.out.println(sc);
sc.configureBlocking(false);
sc.register(selector, SelectionKey.OP_READ);
}
if((sk.readyOps() & SelectionKey.OP_READ) != 0){
ReadableByteChannel rc = (ReadableByteChannel)sk.channel();
sk.interestOps(sk.interestOps() & ~SelectionKey.OP_READ);
ByteBuffer bb = ByteBuffer.allocate(50);
rc.read(bb);
System.out.println(new String(bb.array(),0,bb.position()));
//sk.interestOps(sk.interestOps() | SelectionKey.OP_READ);
Thread anoThread = new Thread(new AnotherThread(sk));
anoThread.start();
anoThread.join();
}
}
}
}
}
}
package com.guojje.nio;
import java.nio.channels.SelectionKey;
public class AnotherThread implements Runnable {
private SelectionKey sk;
public AnotherThread(SelectionKey sk){
this.sk = sk;
}
@Override
public void run() {
sk.interestOps(sk.interestOps() | SelectionKey.OP_READ);
}
}
三、 一个数组byte[] bs = new byte[10],bs[0]=10, bs[1]=9, bs[2]=8
如果想把SocketChannel读入剩余7个元素，而不影响其他，可以这样：
ByteBuffer bb = ByteBuffer.wrap(bs,3,7).slice();
如果仅仅用ByteBuffer.wrap(bs,3,7)，则bb的capacity仍为bs.length.
而用slice之后，bb的capacity为7,所以你对bb的任务操作都不会影响到前三个元素。
package com.guojje.nio;
import java.nio.ByteBuffer;
public class TestSlice {
public static void main(String[] args) {
byte[] bs = new byte[10];
bs[0]=10;
bs[1]=9;
bs[2]=8;
ByteBuffer bb1 = ByteBuffer.wrap(bs,3,7);
ByteBuffer bb2 = ByteBuffer.wrap(bs,3,7).slice();
System.out.println(bb1.capacity());
System.out.println(bb2.capacity());
}
}
四、 ByteBuffer.put ()与 ByteBuffer.get()都会增长position,并且上限都是limit.
因为:
final int nextGetIndex() { // package-private
if (position >= limit)
throw new BufferUnderflowException();
return position++;
}
final int nextPutIndex() { // package-private
if (position >= limit)
throw new BufferOverflowException();
return position++;
}
position都会增长。
五、 一个 channal 对应同一个SelectionKey in the same selector
六、channel.register操作may block if invoked concurrently with another registration[another.register(...)]
or selection operation[selector.select(...)] involving in the same selector.
这是因为register操作需要regLock与keyLock锁。
七. selectionKey.cancel():
The key will be removed from all of the selector's key sets during the next selection operation[select(...)] 。
cancel may block briefly if invoked concurrently with a cancellation[cancel()] or selection operation[select(...)]
involving the same selector.
参考：http://www.blogjava.net/adapterofcoms/archive/2010/03/02/314242.html