Netty权威指南之NIO通信模型

NIO简介：与Socket和ServerSocket类相对应，NIO提供了SocketChannel和ServerSocketChannel两种不同的套接字通道实现，这两种新通道都支持阻塞和非阻塞两种模式。阻塞模式使用简单，但是性能和可靠性不好，非阻塞模式正好相反。

　　1.缓冲区Buffer：一个对象，包含一些要写入或要读出的数据。任何时候访问NIO中数据，都是通过缓冲区进行操作。缓冲区实质是一个数据，最常用的缓冲区是ByteBuffer。每一种Java基本类型都对应一种缓冲区，如ByteBuffer字节缓冲区、CharBuffer字符缓冲区、ShortBuffer短整型缓冲区、IntBuffer整型缓冲区、LongBuffer长整型缓冲区、FloatBuffer浮点型缓冲区、DoubleBuffer双精度浮点型缓冲区

　　2.通道Channel：Channel是一个通道，网络数据通过Channel读取和写入。Channel可以用于读取和写入同时进行，因为通道是全双工的，而流只是在一个方向上移动（一个流必须是InputStream或者OutputStream的子类）。Channel可以分为两大类，用于网络读写的SelectableChannel和用于文件操作的FileChannel

　　3.多路复用器Selector：Selector会不断的轮询注册在其上的Channel，如果某个Channel上面发生读或者写事件，这个Channel就处于就绪状态，会被Selector轮询出来，然后通过SelectionKey可以获取就绪Channel的集合，进行后续的I/O操作。一个多路复用器Selector可以同时轮询多个Channel，由于JDK使用了epoll()代替传统的select实现，所以它并没有最大连接句柄1024/2048的限制，意味着一个线程负责Selector的轮询，就可以接入成千上万的客户端

如果发送区TCP缓冲区满，会导致写半包，此时，需要注册监听写操作位，循环写，直到整包消息写入TCP缓冲区

Server对应Accept，Client对应Connection

package com.hjp.netty.nio;

import java.io.IOException;

public class TimeServer {

    public static void main(String[] args) throws IOException {
        int port = 8080;
        if (args != null && args.length > 0) {
            try {
                port = Integer.valueOf(port);
            } catch (NumberFormatException e) {
                e.printStackTrace();
            }
        }
        //创建多路复用类，一个独立线程，负责轮询多路复用器Selector，可以处理多个客户端的并发接入
        MultiplexerTimeServer timeServer = new MultiplexerTimeServer(port);
        new Thread(timeServer, "NIO-MultiplexerTimeServer-001").start();
    }

}

package com.hjp.netty.nio;

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.Date;
import java.util.Iterator;
import java.util.Set;

public class MultiplexerTimeServer implements Runnable {

    private Selector selector;

    private ServerSocketChannel serverChannel;

    private volatile boolean stop;

    /**
     * 初始化多路复用器，绑定监听端口
     *
     * @param port
     */
    public MultiplexerTimeServer(int port) {
        try {
            selector = Selector.open();
            serverChannel = ServerSocketChannel.open();
            serverChannel.configureBlocking(false);
            serverChannel.socket().bind(new InetSocketAddress(port), 1024);
            serverChannel.register(selector, SelectionKey.OP_ACCEPT);
            System.out.println("The time server is start in port : " + port);
        } catch (IOException e) {
            e.printStackTrace();
            System.exit(1);
        }
    }

    public void stop() {
        this.stop = true;
    }

    @Override
    public void run() {
        while (!stop) {
            try {
                selector.select(1000);//休眠一秒
                Set<SelectionKey> selectedKeys = selector.selectedKeys();
                Iterator<SelectionKey> it = selectedKeys.iterator();
                SelectionKey key = null;
                while (it.hasNext()) {
                    key = it.next();
                    it.remove();
                    try {
                        handleInput(key);
                    } catch (Exception e) {
                        if (key != null) {
                            key.cancel();
                            if (key.channel() != null) {
                                key.channel().close();
                            }
                        }
                    }
                }
            } catch (Throwable t) {
                t.printStackTrace();
            }
        }
        //多路复用器关闭后，所有注册在上面的Channel和Pipe等资源都会被自动去注册并关闭，所有不需要重复释放资源
        if (selector != null) {
            try {
                selector.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    private void handleInput(SelectionKey key) throws IOException {
        if (key.isValid()) {
            //处理新接入的请求消息
            if (key.isAcceptable()) {
                //Accept the new connection
                ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
                SocketChannel sc = ssc.accept();
                sc.configureBlocking(false);
                //Add the new connection to the selector
                sc.register(selector, SelectionKey.OP_READ);
            }
            if (key.isReadable()) {
                //Read the data
                SocketChannel sc = (SocketChannel) key.channel();
                ByteBuffer readBuffer = ByteBuffer.allocate(1024);
                int readBytes = sc.read(readBuffer);
                if (readBytes > 0) {
                    readBuffer.flip();
                    byte[] bytes = new byte[readBuffer.remaining()];
                    readBuffer.get(bytes);
                    String body = new String(bytes, "UTF-8");
                    System.out.println("The time server receive order : " + body);
                    String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body) ? new Date(System.currentTimeMillis()).toString() : "BAD ORDER";
                    doWrite(sc, currentTime);
                } else if (readBytes < 0) {
                    //对端链路关闭
                    key.cancel();
                    sc.close();
                } else {
                    ;//读到0字节，忽略
                }
            }
        }
    }

    private void doWrite(SocketChannel channel, String response) throws IOException {
        if (response != null && response.trim().length() > 0) {
            byte[] bytes = response.getBytes();
            ByteBuffer writeBuffer=ByteBuffer.allocate(bytes.length);
            writeBuffer.put(bytes);
            writeBuffer.flip();
            channel.write(writeBuffer);
        }
    }
}

package com.hjp.netty.nio;

import java.io.IOException;

public class TimeClient {

    public static void main(String[] args) throws IOException {
        int port = 8080;
        if (args != null && args.length > 0) {
            try {
                port = Integer.valueOf(args[0]);
            } catch (NumberFormatException e) {
                e.printStackTrace();
            }
        }
        new Thread(new TimeClientHandler("127.0.0.1",port),"TimeClient-001").start();
    }

}

package com.hjp.netty.nio;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectableChannel;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
import java.util.Set;

public class TimeClientHandler implements Runnable {

    private String host;
    private int port;
    private Selector selector;
    private SocketChannel socketChannel;
    private volatile boolean stop;

    public TimeClientHandler(String host, int port) {
        this.host = host == null ? "127.0.0.1" : host;
        this.port = port;
        try {
            selector = Selector.open();
            socketChannel = SocketChannel.open();
            socketChannel.configureBlocking(false);
        } catch (IOException e) {
            e.printStackTrace();
            System.exit(1);
        }
    }

    @Override
    public void run() {
        try {
            doConnect();
        } catch (IOException e) {
            e.printStackTrace();
            System.exit(1);
        }
        while (!stop) {
            try {
                selector.select(1000);
                Set<SelectionKey> selectedKeys = selector.selectedKeys();
                Iterator<SelectionKey> it = selectedKeys.iterator();
                SelectionKey key = null;
                while (it.hasNext()) {
                    key = it.next();
                    it.remove();
                    try {
                        handleInput(key);
                    } catch (Exception e) {
                        if (key != null) {
                            key.cancel();
                            if (key.channel() != null) {
                                key.channel().close();
                            }
                        }
                    }
                }
            } catch (Exception e) {
                e.printStackTrace();
                System.exit(1);
            }
        }
        //多路复用器关闭后，所有注册在上面的Channel和Pipe等资源都会被自动去注册并关闭，所以不需要重复释放资源
        if (selector != null) {
            try {
                selector.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    private void handleInput(SelectionKey key) throws IOException {
        if (key.isValid()) {
            //判断是否连接成功
            SocketChannel sc = (SocketChannel) key.channel();
            if (key.isConnectable()) {
                if (sc.finishConnect()) {
                    sc.register(selector, SelectionKey.OP_READ);
                    doWrite(sc);
                } else {
                    System.exit(1);//连接失败进程退出
                }
            }
            if (key.isReadable()) {
                ByteBuffer readBuffer = ByteBuffer.allocate(1024);
                int readBytes = sc.read(readBuffer);
                if (readBytes > 0) {
                    readBuffer.flip();
                    byte[] bytes = new byte[readBuffer.remaining()];
                    readBuffer.get(bytes);
                    String body = new String(bytes, "UTF-8");
                    System.out.println("Now is : " + body);
                    this.stop = true;
                } else if (readBytes < 0) {
                    //对端链路关闭
                    key.cancel();
                    sc.close();
                } else {
                    ;//对到0字节，忽略
                }
            }
        }
    }

    private void doConnect() throws IOException {
        //如果直接连接成功，则注册到多路复用器上，发送请求消息，读应答
        if (socketChannel.connect(new InetSocketAddress(host, port))) {
            socketChannel.register(selector, SelectionKey.OP_READ);
            doWrite(socketChannel);
        } else {
            socketChannel.register(selector, SelectionKey.OP_CONNECT);
        }
    }

    private void doWrite(SocketChannel sc) throws IOException {
        byte[] req = "QUERY TIME ORDER".getBytes();
        ByteBuffer writeBuffer = ByteBuffer.allocate(req.length);
        writeBuffer.put(req);
        writeBuffer.flip();
        sc.write(writeBuffer);
        if (!writeBuffer.hasRemaining()) {
            System.out.println("Send order 2 server succeed.");
        }
    }
}