1：selectionKey.channel()方法返回的 channel是ServerSocketChannel还是SocketChannel是由前边注册这个key时是注册channel确定的。
2：基本处理流程
服务器端先注册接收Key
serverSocketChannel.register(selector,SelectionKey.OP_ACCEPT)
while(true){
selector.select();
Set<SelectionKey> keys=selector.selectedKeys();
Iterator it=keys.iterator();
while(it.hasNext()){
SelectionKey key=it.next();
it.remove();
处理key
}
3：一般ServerSocketChannel只注册accept事件，对于read和write事件是注册到accept的SocketChannel中的
public class NIOServer {
/*标识数字*/
private int flag = 0;
/*缓冲区大小*/
private int BLOCK = 4096;
/*接受数据缓冲区*/
private ByteBuffer sendbuffer = ByteBuffer.allocate(BLOCK);
/*发送数据缓冲区*/
private ByteBuffer receivebuffer = ByteBuffer.allocate(BLOCK);
private Selector selector;
public NIOServer(int port) throws IOException {
// 打开服务器套接字通道
ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
// 服务器配置为非阻塞
serverSocketChannel.configureBlocking(false);
// 检索与此通道关联的服务器套接字
ServerSocket serverSocket = serverSocketChannel.socket();
// 进行服务的绑定
serverSocket.bind(new InetSocketAddress(port));
// 通过open()方法找到Selector
selector = Selector.open();
// 注册到selector，等待连接
serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
System.out.println("Server Start----8888:");
}
// 监听
private void listen() throws IOException {
while (true) {
// 选择一组键，并且相应的通道已经打开
selector.select();
// 返回此选择器的已选择键集。
Set<SelectionKey> selectionKeys = selector.selectedKeys();
Iterator<SelectionKey> iterator = selectionKeys.iterator();
while (iterator.hasNext()) {
SelectionKey selectionKey = iterator.next();
iterator.remove();
handleKey(selectionKey);
}
}
}
// 处理请求
private void handleKey(SelectionKey selectionKey) throws IOException {
// 接受请求
ServerSocketChannel server = null;
SocketChannel client = null;
String receiveText;
String sendText;
int count=0;
// 测试此键的通道是否已准备好接受新的套接字连接。
if (selectionKey.isAcceptable()) {
// 返回为之创建此键的通道。
server = (ServerSocketChannel) selectionKey.channel();
// 接受到此通道套接字的连接。
// 此方法返回的套接字通道（如果有）将处于阻塞模式。
client = server.accept();
// 配置为非阻塞
client.configureBlocking(false);
// 注册到selector，等待连接
client.register(selector, SelectionKey.OP_READ);
} else if (selectionKey.isReadable()) {
// 返回为之创建此键的通道。
client = (SocketChannel) selectionKey.channel();
//将缓冲区清空以备下次读取
receivebuffer.clear();
//读取服务器发送来的数据到缓冲区中
count = client.read(receivebuffer);
if (count > 0) {
receiveText = new String( receivebuffer.array(),0,count);
System.out.println("服务器端接受客户端数据--:"+receiveText);
client.register(selector, SelectionKey.OP_WRITE);
}
} else if (selectionKey.isWritable()) {
//将缓冲区清空以备下次写入
sendbuffer.clear();
// 返回为之创建此键的通道。
client = (SocketChannel) selectionKey.channel();
sendText="message from server--" + flag++;
//向缓冲区中输入数据
sendbuffer.put(sendText.getBytes());
//将缓冲区各标志复位,因为向里面put了数据标志被改变要想从中读取数据发向服务器,就要复位
sendbuffer.flip();
//输出到通道
client.write(sendbuffer);
System.out.println("服务器端向客户端发送数据--："+sendText);
client.register(selector, SelectionKey.OP_READ);
}
}
/**
* @param args
* @throws IOException
*/
public static void main(String[] args) throws IOException {
// TODO Auto-generated method stub
int port = 8888;
NIOServer server = new NIOServer(port);
server.listen();
}
}