Java NIO的簡單demo

最近學習了一下NIO的一些api，做了簡單的demo，感覺挺有意思的，有興許的可以一起學習

NIO的上手難度感覺還挺高的，學習曲線有一些，畢竟之前已經習慣了BIO的操作了，一下切過來過來還挺困難的，理清楚了基本的幾個概念就好理解多了，比如channel，buffer，selector，socketChannel，serverSocketChannel這幾個弄清楚基本就可以看得懂NIO的api了，不然連api都很困難弄明白。我是從極客學院看的基礎學習，然後寫的簡單的demo，只是demo而已，基礎學習可以看一下。

服務端程式碼

package org.chao.nio;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
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.nio.charset.Charset;
import java.util.Iterator;

/**
 * server 端
 *
 * @author xiezhengchao
 * @since 2018/4/7 14:32
 */
public class ServerDemo{

    private ByteBuffer readBuffer = ByteBuffer.allocateDirect(1024);
    private ByteBuffer writeBuffer = ByteBuffer.allocateDirect(1024);
    private Selector selector;

    public ServerDemo() throws IOException{
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        serverSocketChannel.configureBlocking(false);
        ServerSocket serverSocket = serverSocketChannel.socket();
        serverSocket.bind(new InetSocketAddress(8080));
        System.out.println("listening on port 8080");

        this.selector = Selector.open();;

        // 繫結channel的accept
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
    }

    public static void main(String[] args) throws Exception{
        new ServerDemo().go();
    }

    private void go() throws Exception{

        // block api
        while(selector.select()>0){

            Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();
            while(iterator.hasNext()){
                SelectionKey selectionKey = iterator.next();
                iterator.remove();
                // 新連線
                if(selectionKey.isAcceptable()){
                    System.out.println("isAcceptable");
                    ServerSocketChannel server = (ServerSocketChannel)selectionKey.channel();

                    // 新註冊channel
                    SocketChannel socketChannel  = server.accept();
                    if(socketChannel==null){
                        continue;
                    }
                    socketChannel.configureBlocking(false);
                     // 注意！這裡和阻塞io的區別非常大，在編碼層面之前的等待輸入已經變成了註冊事件，這樣我們就可以在等待的時候做別的事情，
                    // 比如監聽更多的socket連線，也就是之前說了一個執行緒監聽多個socket連線。這也是在編碼的時候最直觀的感受
                    socketChannel.register(selector, SelectionKey.OP_READ| SelectionKey.OP_WRITE);


                    ByteBuffer buffer = ByteBuffer.allocateDirect(1024);
                    buffer.put("hi new channel".getBytes());
                    buffer.flip();
                    socketChannel.write(buffer);
                }

                // 服務端關心的可讀，意味著有資料從client傳來了，根據不同的需要進行讀取，然後返回
                if(selectionKey.isReadable()){
                    System.out.println("isReadable");
                    SocketChannel socketChannel = (SocketChannel)selectionKey.channel();

                    readBuffer.clear();
                    socketChannel.read(readBuffer);
                    readBuffer.flip();

                    String receiveData= Charset.forName("UTF-8").decode(readBuffer).toString();
                    System.out.println("receiveData:"+receiveData);

                    // 把讀到的資料繫結到key中
                    selectionKey.attach("server message echo:"+receiveData);
                }

                // 實際上服務端不在意這個，這個寫入應該是client端關心的，這只是個demo,順便試一下selectionKey的attach方法
                if(selectionKey.isWritable()){
                    SocketChannel socketChannel = (SocketChannel)selectionKey.channel();

                    String message = (String) selectionKey.attachment();
                    if(message==null){
                        continue;
                    }
                    selectionKey.attach(null);

                    writeBuffer.clear();
                    writeBuffer.put(message.getBytes());
                    writeBuffer.flip();
                    while(writeBuffer.hasRemaining()){
                        socketChannel.write(writeBuffer);
                    }
                }
            }
        }
    }

}

客戶端程式碼

package org.chao.nio;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.InetAddress;
import java.net.InetSocketAddress;
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;

/**
 * client 端
 *
 * @author xiezhengchao
 * @since 2018/4/7 15:10
 */
public class ClientDemo{

    private final ByteBuffer sendBuffer=ByteBuffer.allocate(1024);
    private final ByteBuffer receiveBuffer=ByteBuffer.allocate(1024);
    private Selector selector;

    public ClientDemo()throws IOException{
        SocketChannel socketChannel = SocketChannel.open();
        socketChannel.connect(new InetSocketAddress(InetAddress.getLocalHost(),8080));
        socketChannel.configureBlocking(false);
        System.out.println("與伺服器的連線建立成功");
        selector=Selector.open();
        socketChannel.register(selector,SelectionKey.OP_READ | SelectionKey.OP_WRITE);
    }

    public static void main(String[] args) throws Exception{
        final ClientDemo client=new ClientDemo();
        Thread receiver=new Thread(client::receiveFromUser);

        receiver.start();
        client.talk();
    }

    private void talk()throws IOException {
        while (selector.select() > 0 ){

            Iterator<SelectionKey> it = selector.selectedKeys().iterator();
            while (it.hasNext()){
                SelectionKey key = it.next();
                it.remove();

                if (key.isReadable()) {
                    receive(key);
                }
                // 實際上只要註冊了關心寫操作，這個操作就一直被啟用
                if (key.isWritable()) {
                    send(key);
                }
            }

        }
    }

    private void send(SelectionKey key)throws IOException{
        SocketChannel socketChannel=(SocketChannel)key.channel();
        synchronized(sendBuffer){
            sendBuffer.flip(); //設定寫
            while(sendBuffer.hasRemaining()){
                socketChannel.write(sendBuffer);
            }
            sendBuffer.compact();
        }
    }
    private void receive(SelectionKey key)throws IOException{
        SocketChannel socketChannel=(SocketChannel)key.channel();
        socketChannel.read(receiveBuffer);
        receiveBuffer.flip();
        String receiveData=Charset.forName("UTF-8").decode(receiveBuffer).toString();

        System.out.println("receive server message:"+receiveData);
        receiveBuffer.clear();
    }

    private void receiveFromUser() {
        BufferedReader bufferedReader=new BufferedReader(new InputStreamReader(System.in));
        try{
            String msg;
            while ((msg = bufferedReader.readLine()) != null){
                synchronized(sendBuffer){
                    sendBuffer.put((msg+"\r\n").getBytes());
                }
            }
        }catch(Exception e){
            e.printStackTrace();
        }
    }
}

如果不啟用客戶端程式碼進行測試也可以用telnet命令進行測試telnet 127.0.0.1 8080

telnet命令測試服務端