Java中NIO及基础实现

NIO:同步非阻塞IO

来源：BIO是同步阻塞IO操作，当线程在处理任务时，另一方会阻塞着等待该线程的执行完毕，为了提高效率，，JDK1.4后，引入NIO来提升数据的通讯性能

NIO中采用Reactor设计模式，注册的汇集点为Selector，NIO有三个主要组成部分：Channel（通道）、Buffer（缓冲区）、Selector（选择器）

Reactor设计模式：Reactor模式是一种被动事件处理模式，即当某个特定事件发生时触发事件，可参考，https://blog.csdn.net/feimataxue/article/details/7642638，https://www.cnblogs.com/bitkevin/p/5724410.html

NIO采用了轮询的方式来观察事件是否执行完毕，如：A让B打印某个文件，BIO会一直等待着B返回，期间自己不做其他事情，而NIO则会不断的询问B是否完成，未完成则处理自己的时，直至B完成

Channel（通道）：Channel是一个对象，可以通过它读取和写入数据

Selector（对象选择器）： Selector是一个对象，它可以注册到很多个Channel上，监听各个Channel上发生的事件，并且能够根据事件情况决定Channel读写

代码实现：（此实现参考网络上可用的例子）

NIO客户端实现：

package com.learn.nio.client;

import com.study.info.HostInfo;
import com.study.util.InputUtil;

import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SocketChannel;

public class NIOEchoClient {

    public static void main(String[] args) throws Exception{
        SocketChannel clientChannel = SocketChannel.open();
        clientChannel.connect(new InetSocketAddress(HostInfo.HOST_NAME,HostInfo.PORT));
        ByteBuffer buffer = ByteBuffer.allocate(50);
        boolean flag = true;
        while (flag){
            buffer.clear();
            String input = InputUtil.getString("请输入待发送的信息：").trim();
            buffer.put(input.getBytes());   //将数据存入缓冲区
            buffer.flip();  //  重置缓冲区
            clientChannel.write(buffer);    //发送数据
            buffer.clear();
            int read = clientChannel.read(buffer);
            buffer.flip();
            System.err.print(new String(buffer.array(), 0, read));
            if("byebye".equalsIgnoreCase(input)){
                flag = false;
            }
        }
        clientChannel.close();
    }
}

NIO服务端实现：

package com.learn.nio.server;

import com.study.info.HostInfo;

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;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class NIOEchoServer {

    private static class EchoClientHandle implements Runnable {

        //客户端
        private SocketChannel clientChannel;
        // 循环结束标记
        private boolean flag = true;
        public EchoClientHandle(SocketChannel clientChannel){
            this.clientChannel = clientChannel;
        }

        @Override
        public void run() {
            ByteBuffer byteBuffer = ByteBuffer.allocate(50);
            try {
                while (this.flag){
                    byteBuffer.clear();
                    int read = this.clientChannel.read(byteBuffer);
                    String msg = new String(byteBuffer.array(), 0, read).trim();
                    String outMsg = "【Echo】" + msg + "\n"; // 回应信息
                    if("byebve".equals(msg)){
                        outMsg = "会话结束，下次再见！";
                        this.flag = false;
                    }
                    byteBuffer.clear();
                    byteBuffer.put(outMsg.getBytes());  //回传信息放入缓冲区
                    byteBuffer.flip();
                    this.clientChannel.write(byteBuffer);// 回传信息
                }
            }catch (Exception e){
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) throws Exception{
        // 为了性能问题及响应时间，设置固定大小的线程池
        ExecutorService executorService = Executors.newFixedThreadPool(10);
        // NIO基于Channel控制，所以有Selector管理所有的Channel
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        // 设置为非阻塞模式
        serverSocketChannel.configureBlocking(false);
        // 设置监听端口
        serverSocketChannel.bind(new InetSocketAddress(HostInfo.PORT));
        // 设置Selector管理所有Channel
        Selector selector = Selector.open();
        // 注册并设置连接时处理
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
        System.out.println("服务启动成功，监听端口为：" + HostInfo.PORT);
        // NIO使用轮询，当有请求连接时，则启动一个线程
        int keySelect = 0;
        while ((keySelect = selector.select()) > 0){
            Set<SelectionKey> selectionKeys = selector.selectedKeys();
            Iterator<SelectionKey> iterator = selectionKeys.iterator();
            while (iterator.hasNext()){
                SelectionKey next = iterator.next();
                if(next.isAcceptable()){    //  如果是连接的
                    SocketChannel accept = serverSocketChannel.accept();
                    if(accept != null){
                        executorService.submit(new EchoClientHandle(accept));
                    }
                    iterator.remove();
                }
            }
        }
        executorService.shutdown();
        serverSocketChannel.close();
    }
}

工具类：

package com.study.util;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class InputUtil {
    private static final BufferedReader KEYBOARD_INPUT = new BufferedReader(new InputStreamReader(System.in));

    private InputUtil(){
    }

    public static String getString(String prompt){
        boolean flag = true;    //数据接受标记
        String str = null;
        while (flag){
            System.out.println(prompt);
            try {
                str = KEYBOARD_INPUT.readLine();    // 读取一行数据
                if(str == null || "".equals(str)){
                    System.out.println("数据输入错误，不允许为空！");
                }else {
                    flag = false;
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return str;
    }
}

package com.study.info;

public calss HostInfo {
    public static final String HOST_NAME = "localhost";
    public static final int PORT = 9999;
}

NIO结构参考文章： https://www.cnblogs.com/sxkgeek/p/9488703.html#_label2