不知归期1，netty系列之:NIO和netty详解
简介
netty为什么快呢？这是因为netty底层使用了JAVA的NIO技术，并在其基础上进行了性能的优化，虽然netty不是单纯的JAVA nio，但是netty的底层还是基于的是nio技术。
nio是JDK1.4中引入的，用于区别于传统的IO，所以nio也可以称之为new io。
nio的三大核心是Selector,channel和Buffer，本文我们将会深入探究NIO和netty之间的关系。
NIO常用用法
在讲解netty中的NIO实现之前，我们先来回顾一下JDK中NIO的selector，channel是怎么工作的。对于NIO来说selector主要用来接受客户端的连接，所以一般用在server端。我们以一个NIO的服务器端和客户端聊天室为例来讲解NIO在JDK中是怎么使用的。
因为是一个简单的聊天室，我们选择Socket协议为基础的ServerSocketChannel,首先就是open这个Server channel:
ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
serverSocketChannel.bind(new InetSocketAddress("localhost", 9527));
serverSocketChannel.configureBlocking(false);
然后向server channel中注册selector:
Selector selector = Selector.open();
serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
虽然是NIO，但是对于Selector来说，它的select方法是阻塞方法，只有找到匹配的channel之后才会返回，为了多次进行select操作，我们需要在一个while循环里面进行selector的select操作：
while (true) {
selector.select();
Set<SelectionKey> selectedKeys = selector.selectedKeys();
Iterator<SelectionKey> iter = selectedKeys.iterator();
while (iter.hasNext()) {
SelectionKey selectionKey = iter.next();
if (selectionKey.isAcceptable()) {
register(selector, serverSocketChannel);
}
if (selectionKey.isReadable()) {
serverResponse(byteBuffer, selectionKey);
}
iter.remove();
}
Thread.sleep(1000);
}
selector中会有一些SelectionKey,SelectionKey中有一些表示操作状态的OP Status,根据这个OP Status的不同，selectionKey可以有四种状态，分别是isReadable,isWritable,isConnectable和isAcceptable。
当SelectionKey处于isAcceptable状态的时候，表示ServerSocketChannel可以接受连接了，我们需要调用register方法将serverSocketChannel accept生成的socketChannel注册到selector中，以监听它的OP READ状态，后续可以从中读取数据：
private static void register(Selector selector, ServerSocketChannel serverSocketChannel)
throws IOException {
SocketChannel socketChannel = serverSocketChannel.accept();
socketChannel.configureBlocking(false);
socketChannel.register(selector, SelectionKey.OP_READ);
}
当selectionKey处于isReadable状态的时候，表示可以从socketChannel中读取数据然后进行处理：
private static void serverResponse(ByteBuffer byteBuffer, SelectionKey selectionKey)
throws IOException {
SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
socketChannel.read(byteBuffer);
byteBuffer.flip();
byte[] bytes= new byte[byteBuffer.limit()];
byteBuffer.get(bytes);
log.info(new String(bytes).trim());
if(new String(bytes).trim().equals(BYE_BYE)){
log.info("说再见不如不见！");
socketChannel.write(ByteBuffer.wrap("再见".getBytes()));
socketChannel.close();
}else {
socketChannel.write(ByteBuffer.wrap("你是个好人".getBytes()));
}
byteBuffer.clear();
}
上面的serverResponse方法中，从selectionKey中拿到对应的SocketChannel，然后调用SocketChannel的read方法，将channel中的数据读取到byteBuffer中，要想回复消息到channel中，还是使用同一个socketChannel，然后调用write方法回写消息给client端，到这里一个简单的回写客户端消息的server端就完成了。
接下来就是对应的NIO客户端，在NIO客户端需要使用SocketChannel,首先建立和服务器的连接：
socketChannel = SocketChannel.open(new InetSocketAddress("localhost", 9527));
然后就可以使用这个channel来发送和接受消息了：
public String sendMessage(String msg) throws IOException {
byteBuffer = ByteBuffer.wrap(msg.getBytes());
String response = null;
socketChannel.write(byteBuffer);
byteBuffer.clear();
socketChannel.read(byteBuffer);
byteBuffer.flip();
byte[] bytes= new byte[byteBuffer.limit()];
byteBuffer.get(bytes);
response =new String(bytes).trim();
byteBuffer.clear();
return response;
}
<div class="cnblogs_code">
<pre><span style="color: #000000;">
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pythonpython
</span></pre>
</div>
