NIO：non-blocking input output

NIO核心类

Channel

1. 类似于Stream，但是是双向的
2. 非阻塞性
3. 操作唯一性，通过Buffer
   文件类：FileChannel
   UDP类：DatagramChannel
   TCP类：ServerSocketChannel/SocketChannel
   使用：

//服务器通过Socket创建channel
ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
//绑定端口
serverSocketChannel.bind(new InetSocketAddress(8000));
//监听客户端连接，建立socketChannel连接
SocketChannel socketChannel = serverSocketChannel.accept();
//客户端连接远成主机
SocketChannel socketChannel = SocketChannel.open(new InetSocketAddress("127.0.0.1", 8000));

Buffer

作用：读写Channel中的数据
属性：

1. Capacity
2. Position
3. Limit
4. Mark
   使用：

//初始化长度为10的Buffer
ByteBuffer byteBuffer = ByteBuffer.allocate(10);
//写入数据
byteBuffer.put("abc", getBytes(Charset.forName("UTF-8")));
//将写切换为读
byteBuffer.flip();
byteBuffer.get();
//记录当前position的位置
byteBuffer.mark();
//回到mark标记的位置
byteBuffer.reset();
byteBuffer.clear();

Selector

作用：I/O就绪选择
使用：

//创建selector
Selector selector = Selector.open();
//将channel注册到selector上，监听就绪事件
SelectionKey selectionKey = channel.register(selector, SelectionKey.OP_READ):
//阻塞等待channel有就绪事件发生
int selectNum = selector.select();
//获取发生就绪事件的channel集合
Set<SelectionKey> selectedKey = selector.selectedKeys(); 

实战-网络聊天室

基本功能：一个客户端发消息其他客户端能收到消息。
客户端：

1. 连接服务端
2. 接收服务端响应
3. 发送消息给服务端

package com.imooc;import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.nio.charset.Charset;
import java.util.Scanner;/*** NIO客户端*/
public class NioClient {/*** 启动*/public void start(String nickname) throws IOException {/*** 连接服务器端*/SocketChannel socketChannel = SocketChannel.open(new InetSocketAddress("127.0.0.1", 8000));/*** 接收服务器端响应*/// 新开线程，专门负责来接收服务器端的响应数据// selector ， socketChannel ， 注册Selector selector = Selector.open();socketChannel.configureBlocking(false);socketChannel.register(selector, SelectionKey.OP_READ);new Thread(new NioClientHandler(selector)).start();/*** 向服务器端发送数据*/Scanner scanner = new Scanner(System.in);while (scanner.hasNextLine()) {String request = scanner.nextLine();if (request != null && request.length() > 0) {socketChannel.write(Charset.forName("UTF-8").encode(nickname + " : " + request));}}}public static void main(String[] args) throws IOException {
//        new NioClient().start();}}

客户端响应服务端发过来的消息

1. 给客户端添加一个Selector，当服务端有消息过来的时候，Selector去告诉客户端。
2. 通过selector.selectedKeys()来获取可以用的channel
3. 判断是哪种SelectionKey
4. 让对应的Handler去处理

package com.imooc;import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.nio.charset.Charset;
import java.util.Iterator;
import java.util.Set;/*** 客户端线程类，专门接收服务器端响应信息*/
public class NioClientHandler implements Runnable {private Selector selector;public NioClientHandler(Selector selector) {this.selector = selector;}@Overridepublic void run() {try {for (;;) {int readyChannels = selector.select();if (readyChannels == 0) continue;/*** 获取可用channel的集合*/Set<SelectionKey> selectionKeys = selector.selectedKeys();Iterator iterator = selectionKeys.iterator();while (iterator.hasNext()) {/*** selectionKey实例*/SelectionKey selectionKey = (SelectionKey) iterator.next();/*** **移除Set中的当前selectionKey***/iterator.remove();/*** 7. 根据就绪状态，调用对应方法处理业务逻辑*//*** 如果是 可读事件*/if (selectionKey.isReadable()) {readHandler(selectionKey, selector);}}}} catch (IOException e) {e.printStackTrace();}}/*** 可读事件处理器*/private void readHandler(SelectionKey selectionKey, Selector selector)throws IOException {/*** 要从 selectionKey 中获取到已经就绪的channel*/SocketChannel socketChannel = (SocketChannel) selectionKey.channel();/*** 创建buffer*/ByteBuffer byteBuffer = ByteBuffer.allocate(1024);/*** 循环读取服务器端响应信息*/String response = "";while (socketChannel.read(byteBuffer) > 0) {/*** 切换buffer为读模式*/byteBuffer.flip();/*** 读取buffer中的内容*/response += Charset.forName("UTF-8").decode(byteBuffer);}/*** 将channel再次注册到selector上，监听他的可读事件*/socketChannel.register(selector, SelectionKey.OP_READ);/*** 将服务器端响应信息打印到本地*/if (response.length() > 0) {System.out.println(response);}}
}

注意：每次用完Channel后都要再次把它注册到Selector上
服务端：
服务端主要作用就是对聊天消息的转发

package com.imooc;import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.nio.charset.Charset;
import java.util.Iterator;
import java.util.Set;/*** NIO服务器端*/
public class NioServer {/*** 启动*/public void start() throws IOException {/*** 1. 创建Selector*/Selector selector = Selector.open();/*** 2. 通过ServerSocketChannel创建channel通道*/ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();/*** 3. 为channel通道绑定监听端口*/serverSocketChannel.bind(new InetSocketAddress(8000));/*** 4. **设置channel为非阻塞模式***/serverSocketChannel.configureBlocking(false);/*** 5. 将channel注册到selector上，监听连接事件*/serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);System.out.println("服务器启动成功！");/*** 6. 循环等待新接入的连接*/for (;;) { // while(true) c for;;/*** TODO 获取可用channel数量*/int readyChannels = selector.select();/*** TODO 为什么要这样！！？*/if (readyChannels == 0) continue;/*** 获取可用channel的集合*/Set<SelectionKey> selectionKeys = selector.selectedKeys();Iterator iterator = selectionKeys.iterator();while (iterator.hasNext()) {/*** selectionKey实例*/SelectionKey selectionKey = (SelectionKey) iterator.next();/*** **移除Set中的当前selectionKey***/iterator.remove();/*** 7. 根据就绪状态，调用对应方法处理业务逻辑*//*** 如果是 接入事件*/if (selectionKey.isAcceptable()) {acceptHandler(serverSocketChannel, selector);}/*** 如果是 可读事件*/if (selectionKey.isReadable()) {readHandler(selectionKey, selector);}}}}/*** 接入事件处理器*/private void acceptHandler(ServerSocketChannel serverSocketChannel,Selector selector)throws IOException {/*** 如果要是接入事件，创建socketChannel*/SocketChannel socketChannel = serverSocketChannel.accept();/*** 将socketChannel设置为非阻塞工作模式*/socketChannel.configureBlocking(false);/*** 将channel注册到selector上，监听 可读事件*/socketChannel.register(selector, SelectionKey.OP_READ);/*** 回复客户端提示信息*/socketChannel.write(Charset.forName("UTF-8").encode("你与聊天室里其他人都不是朋友关系，请注意隐私安全"));}/*** 可读事件处理器*/private void readHandler(SelectionKey selectionKey, Selector selector)throws IOException {/*** 要从 selectionKey 中获取到已经就绪的channel*/SocketChannel socketChannel = (SocketChannel) selectionKey.channel();/*** 创建buffer*/ByteBuffer byteBuffer = ByteBuffer.allocate(1024);/*** 循环读取客户端请求信息*/String request = "";while (socketChannel.read(byteBuffer) > 0) {/*** 切换buffer为读模式*/byteBuffer.flip();/*** 读取buffer中的内容*/request += Charset.forName("UTF-8").decode(byteBuffer);}/*** 将channel再次注册到selector上，监听他的可读事件*/socketChannel.register(selector, SelectionKey.OP_READ);/*** 将客户端发送的请求信息 广播给其他客户端*/if (request.length() > 0) {// 广播给其他客户端broadCast(selector, socketChannel, request);}}/*** 广播给其他客户端*/private void broadCast(Selector selector,SocketChannel sourceChannel, String request) {/*** 获取到所有已接入的客户端channel*/Set<SelectionKey> selectionKeySet = selector.keys();/*** 循环向所有channel广播信息*/selectionKeySet.forEach(selectionKey -> {Channel targetChannel = selectionKey.channel();// 剔除发消息的客户端if (targetChannel instanceof SocketChannel&& targetChannel != sourceChannel) {try {// 将信息发送到targetChannel客户端((SocketChannel) targetChannel).write(Charset.forName("UTF-8").encode(request));} catch (IOException e) {e.printStackTrace();}}});}/*** 主方法* @param args*/public static void main(String[] args) throws IOException {new NioServer().start();}}

重点注意broadCast方法