一、案例
1、编写一个NIO入门案例，实现服务器端和客户端之间的数据简单通讯（非阻塞）
2、目的：理解NIO非阻塞网络编程机制
3、代码

NIOServer.java

package netty.niostart;import java.io.IOException;
import java.net.InetSocketAddress;
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;
import java.util.Set;public class NIOServer {public static void main(String[] args) throws Exception {//创建ServerSocketChannel -> 类似于ServerSocketServerSocketChannel serverSocketChannel = ServerSocketChannel.open();//得到一个Selector对象Selector selector = Selector.open();//绑定一个端口6666，在服务器端监听serverSocketChannel.socket().bind(new InetSocketAddress(6666));//设置为非阻塞serverSocketChannel.configureBlocking(false);//把serverSocketChannel注册到selector，关心事件为OP_ACCEPTserverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);//循环等待客户端连接while(true) {if (selector.select(5*1000) == 0) {//等待5秒钟，如果没有事件发生，返回System.out.println("服务器等待了5秒，无连接");continue;}//如果返回的>0，就获取到相关的selectionKey集合//1.如果返回的>0，表示已经获取到关注的事件//2.selector.selectedKeys()返回关注的集合//3.通过selectionKeys反向获取通道Set selectionKeys = selector.selectedKeys();//遍历集合Iterator keyIterator = selectionKeys.iterator();while (keyIterator.hasNext()) {//获取到SelectionKeySelectionKey key = keyIterator.next();//根据key，对应的通道发生的事件，做相应的处理if (key.isAcceptable()) {//如果是OP_ACCEPT，有新的客户端连接//给该客户端生成一个SocketChannelSocketChannel socketChannel = serverSocketChannel.accept();//将socketChannel设置为非阻塞模式socketChannel.configureBlocking(false);//将客户端的socketChannel也注册到selector，关注事件为SelectionKey.OP_READ//同时给该socketChannel关联一个buffersocketChannel.register(selector, SelectionKey.OP_READ, ByteBuffer.allocate(10240));System.out.println("from " + socketChannel.hashCode() + " 客户端建立了连接");} else if (key.isReadable()) {//发生OP_READ//通过key反向获取到对应的channelSocketChannel socketChannel = (SocketChannel)key.channel();//获取到该channel关联的bufferByteBuffer byteBuffer = (ByteBuffer)key.attachment();byteBuffer.clear();//把当前通道的数据读到buffer中try {if (socketChannel.read(byteBuffer) == -1) {System.out.println("from " + socketChannel.hashCode() + " 客户端断开了连接");keyIterator.remove();socketChannel.close();continue;}//解析客户端数据//socket通讯格式可以自己定义：4字节报文长度+报文体String request = new String(byteBuffer.array(), 0, byteBuffer.position(), "utf-8");System.out.println("from " + socketChannel.hashCode() + " 客户端：" + request);//----------------------------------------------------------------///*** 业务模块处理（能否做成异步，传入socketChannel对象）主线程只负责网络IO读写*///业务处理System.out.println("业务处理...");//使用新buffer返回ByteBuffer newByteBuffer = ByteBuffer.allocate(10240);newByteBuffer.clear();//获取返回数据String response = "result ok";newByteBuffer.put(response.getBytes("utf-8"));newByteBuffer.put((byte)'9');//注册写事件socketChannel.register(selector, SelectionKey.OP_WRITE, newByteBuffer);//----------------------------------------------------------------//} catch (IOException ioe) {ioe.printStackTrace();keyIterator.remove();socketChannel.close();continue;}} else if (key.isWritable()) {//通过key反向获取到对应的channelSocketChannel socketChannel = (SocketChannel)key.channel();//获取到该channel关联的bufferByteBuffer byteBuffer = (ByteBuffer)key.attachment();//读写切换byteBuffer.flip(); //只有buffer出数据需要切换//把buffer数据写入到channeltry {socketChannel.write(byteBuffer);} catch (IOException ioe) {ioe.printStackTrace();keyIterator.remove();socketChannel.close();continue;}String response = new String(byteBuffer.array(), 0, byteBuffer.position(), "utf-8");System.out.println("to " + socketChannel.hashCode() + " 服务端：" + response);//如果长连接继续注册事件等待//注册读事件//socketChannel.register(selector, SelectionKey.OP_READ, ByteBuffer.allocate(10240));//如果短连接则断开socketChannel.close();} else if (key.isConnectable()) {System.out.println("Connectable");} else if (key.isValid()) {System.out.println("Valid");}//手动从集合中移除当前的SelectionKey，防止重复操作keyIterator.remove();}}}
}

NIOClient.java

package netty.niostart;import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SocketChannel;public class NIOClient {public static void main(String[] args) throws Exception {//得到一个网络通道SocketChannel socketChannel = SocketChannel.open();//设置非阻塞模式socketChannel.configureBlocking(false);//提供服务器端的ip和端口InetSocketAddress inetSocketAddress = new InetSocketAddress("127.0.0.1", 6666);//连接服务器if (!socketChannel.connect(inetSocketAddress)) {while(!socketChannel.finishConnect()) {System.out.println("因为连接需要时间，客户端不会阻塞，可以做其他工作");}}//如果连接成功，就发送数据String str = "111";//客户端也要关联bufferByteBuffer byteBuffer = ByteBuffer.wrap(str.getBytes("utf-8")); //根据字节数组产生buffer//Thread.sleep(30*1000); //模拟线程阻塞//发送数据//将buffer数据写入channelsocketChannel.write(byteBuffer);//获取返回byteBuffer.clear();int numBytesRead;while ((numBytesRead = socketChannel.read(byteBuffer)) != -1) { //-1是读完if (numBytesRead == 0) { //0是读到0个if (byteBuffer.limit() == byteBuffer.position()) {byteBuffer.clear();}continue;}//buffer是数组用这个//System.out.println("客户端收到：" + new String(byteBuffer.array(), byteBuffer.arrayOffset(), byteBuffer.arrayOffset()+byteBuffer.position(), "utf-8"));//单个buffer用这个System.out.println("客户端收到：" + new String(byteBuffer.array(), 0, byteBuffer.position(), "utf-8"));}System.out.println("断开连接...");socketChannel.close();//System.in.read();}
}

二、用telnet测试
1、打开cmd
2、执行：chcp 65001，将编码方式改为“utf-8”
3、telnet连接
4、按Ctrl + ]
5、执行send xxx
6、但是telnet传输字符长度有限制？

三、服务端设想

1、前端请求建立socket连接
2、网络通讯为NIO模型
3、将请求消息和socketChannel对象传到一个队列
4、业务模块维护一个线程池从队列获取请求并处理，还是一请求一线程模式
5、业务线程处理完成后注册写事件，结束
这样网络读写是异步的，通讯和业务处理也是异步的