1.key.attachment为空？ sc.register(selector, SelectionKey.OP_WRITE|SelectionKey.OP_READ,bb); 使用这种方法注册事件时，需要添加第三个参数：attachment对象；或者使用 key.interestOps(SelectionKey.OP_WRITE | SelectionKey.OP_READ)方法;
2.如何捕捉到客户端断开事件？断开时会触发readable key，所以在isreadable中判断read的返回值是否为-1
3.如果不注册写事件则写操作无疑和同步方式一样了，如果注册了写事件则需要在写完时取消该事件
4.key.cancel会同时取消读与写事件
package my;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
public class NIOS {
public static final int SIZE = 1024;
void start(int port) {
ByteBuffer buffer = ByteBuffer.allocate(SIZE);
try {
ServerSocketChannel s = ServerSocketChannel.open();
ServerSocket socket = s.socket();
Selector selector = Selector.open();
InetSocketAddress addr = new InetSocketAddress(port);
socket.bind(addr);
s.configureBlocking(false);
s.register(selector, SelectionKey.OP_ACCEPT);
while (true) {
int selCount = selector.select();
Iterator<SelectionKey> keys = selector.selectedKeys().iterator();
while (keys.hasNext()) {
System.out.println("select Count:" + selCount);
SelectionKey key = (SelectionKey) keys.next();
keys.remove();
if (key.isAcceptable()) {
System.out.println("isacc...");
ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
SocketChannel sc = ssc.accept();
sc.configureBlocking(false);
sc.register(selector, SelectionKey.OP_READ);
} else if (key.isReadable()) {
System.out.println("readable..");
SocketChannel sc = (SocketChannel) key.channel();
try {
int count = sc.read(buffer);
System.out.println("Read byte:" + count);
//log(buffer);
if(count==SIZE){
//如果count等于缓冲区大小，则说明此条消息没读完
//需要设计复杂点的消息结构
}else
if (count == -1) {
//当客户端断开连接时会触发read事件，并且可以读到-1，这时关闭通道
sc.close();
key.cancel();
continue;
}
} catch (Exception e) {
// TODO: handle exception
sc.close();
key.cancel();
System.out.println("close!");
continue;
}
buffer.flip();
ByteBuffer bb = buffer.duplicate();
key.attach(bb);
buffer.clear();
// sc.register(selector,
// SelectionKey.OP_WRITE|SelectionKey.OP_READ,bb);
//等价于
key.interestOps(SelectionKey.OP_WRITE | SelectionKey.OP_READ);
//通常不会注册写事件，除非写的内容巨大，注册写事件后注意取消
} else if (key.isWritable()) {
System.out.println("writable..");
SocketChannel sc = (SocketChannel) key.channel();
ByteBuffer att = (ByteBuffer) key.attachment();
if (att.hasRemaining()) {
int count = sc.write(att);
System.out.println("write:" + count + " byte,hasRemain:" + att.hasRemaining());
} else {
//写完后取消可写事件，仅监听可读事件
key.interestOps(SelectionKey.OP_READ);
}
}
}
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public static void log(ByteBuffer buf){
try {
System.out.println(new String(buf.array(),0,buf.limit(),"utf8"));
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public static void main(String[] args) {
new NIOS().start(802);
}
}