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@@ -0,0 +1,146 @@
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+## NIO
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+
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+---
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+
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+#### 简介：
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+NIO 是java 1.4引入的新特性。是对原来的standard IO的扩展。
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+
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+Standard IO是对字节流的读写，在进行IO之前，首先创建一个流对象，流对象进行读写操作都是按字节
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+，一个字节一个字节的来读或写。而NIO把IO抽象成块，类似磁盘的读写，每次IO操作的单位都是一个块，块被读入内存之后就是一个byte[]，NIO一次可以读或写多个字节。
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+
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+
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+#####NIO的几大组件：
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+
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+#####1.Selector
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+多路复用选择器，基于“事件驱动”
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+
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+* 创建多路复用器并启动线程
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+
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+```
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+ Selector selector=Selector.open();
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+ new Thread(new ReactorTask()).start();
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+
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+```
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+
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+* 创建Channel
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+
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+```
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+// 打开ServerSocketChannel，用于监听客户端的连接
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+ServerSocketChannel ssc=ServerSocketChannel.open();
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+//设置连接为非阻塞模式
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+ssc.configureBlocking(false);
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+//绑定监听端口
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+ServerSocket ss=ssc.socket();
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+ss.bind(new InetSocketAddress(InetAdderss.getByName("ip"),port));
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+//将ServerSocketChannel注册到多路复用器Selector上，监听ACCEPT事件
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+ssc.register(selector,SelectionKey.OP_ACCEPT);
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+
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+```
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+* 等待客户端的连接
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+
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+```
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+ while (true) {
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+ // selector.select是阻塞的，一直等到有客户端连接过来才返回，然后会检查发生的是哪一种事件，然后根据不同的事件做不同的操作
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+ selector.select();
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+ Set<SelectionKey> selectionKeys = selector.selectedKeys();
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+ Iterator<SelectionKey> it = selectionKeys.iterator();
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+ while (it.hasNext()) {
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+ SelectionKey key = it.next();
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+ if (key.isAcceptable()) {
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+ // 处理新接入的请求消息
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+ ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
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+ SocketChannel sc = ssc.accept();
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+ sc.configureBlocking(false);
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+ // 注册读事件
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+ sc.register(selector, SelectionKey.OP_READ);
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+ }
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+ if (key.isReadable()) {
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+ // 处理读请求
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+ SocketChannel sc = (SocketChannel) key.channel();
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+ ByteBuffer readBuffer = ByteBuffer.allocate(1024);
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+ int readBytes = sc.read(readBuffer);
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+ if (readBytes > 0) {
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+ readBuffer.flip();
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+ byte[] bytes = new byte[readBuffer.remaining()];
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+ readBuffer.get(bytes);
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+ System.out.println(new String(bytes, "UTF-8"));
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+ }
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+ }
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+
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+ }
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+ }
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+
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+```
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+
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+
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+#####2.Channel
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+Channel是NIO对IO抽象的一个新概念，NIO在进行IO时需要创建一个Channel对象，是双向的，不象Standard IO分为输入流和输出流
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+
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+#####3.Buffer
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+
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+Buffer和Channel都是一起使用的，每次都是从一个Channel中读出一个Buffer或者把一个Buffer写入到一个Channel中
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+
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+```
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+ // 处理读请求
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+ SocketChannel sc = (SocketChannel) key.channel();
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+ ByteBuffer readBuffer = ByteBuffer.allocate(1024);
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+ int readBytes = sc.read(readBuffer);
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+ if (readBytes > 0) {
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+ readBuffer.flip();
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+ byte[] bytes = new byte[readBuffer.remaining()];
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+ readBuffer.get(bytes);
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+ System.out.println(new String(bytes, "UTF-8"));
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+ }
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+
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+```
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+
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+Buffer有3个重要的属性
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+
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+* position 正整数，指向Buffer中下一个要读取或写入的字节位置
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+* limit 正整数，指向Buffer中的某个位置，在IO时只读写下标小于limit的字节内容
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+* capacity 正整数，Buffer所能容纳的最大字节数
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+
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+0 <= position <= limit <= capacity
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+
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+初始状态：
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+
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+
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+从Channel中读入5个字到ByteBuffer
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+
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+
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+flip()，准备写入或输出
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+
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+```
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+public final Buffer flip() {
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+ limit = position;
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+ position = 0;
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+ mark = -1;
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+ return this;
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+ }
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+```
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+
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+
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+输出内容后，position就移动到跟limit相同的位置上
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+
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+
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+ByteBuffer如果要重复利用，需要清理，position和limit回到初始状态时的位置，然后可以接着用这个Buffer来读写数据，不需要再New 新的Buffer
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+
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+```
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+ public final Buffer clear() {
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+ position = 0;
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+ limit = capacity;
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+ mark = -1;
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+ return this;
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+ }
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+```
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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wenwan
