NIO编程

相关概念

• 缓冲区Buffer
  Buffer是一个对象，它包含一些要写入或者要读出的数据。在NIO库中，所有数据都是用缓冲区处理的。缓冲区实质上是一个数组，最常用的缓冲区是ByteBuffer。

• 通道 Channel
  通道像一个自来水管一样，网络数据通过Channel读取和写入。其和流的区别是，流只能在一个方向上移动，而通道可以用于读、写或者二者同时进行。

• 多路复用器 Selector
  多路复用器提供选择就绪的任务的能力。简单来说Selector会不断的轮询注册在其上的Channel。

NIO服务端时序图

1. 打开ServerSocketChannel，用于监听客户端的连接，它是所有客户端连接的父通道。
2. 绑定监听的端口，设置为非阻塞模式
3. 创建Reactor线程，创建多路复用器并启动线程
4. 将ServerSocketChannel注册到Reactor线程的多路复用器Selector上，监听ACCEPT事件
5. 多路复用器在线程run方法的无限循环体内轮询准备就绪的Key
6. 多路复用器监听到有新的客户端接入，处理新的接入请求，完成TCP三次握手，建立物理链路。
7. 设置客户端链路为非阻塞模式。
8. 将新接入的客户端连接注册到Reactor线程的多路复用器上，监听读操作，读取客户端发送的网络消息。
9. 异步读取客户端请求消息到缓冲区
10. 对ByteBuffer进行编解码，如果有半包消息指针reset，继续读取后续的报文，将解码成功的消息封装成Task，投递到业务线程池中，进行业务逻辑编排。
11. 将POJO对象encode成ByteBuffer，调用SocketChannel异步写入接口，将消息异步发送给客户端。

NIO改造后的TimeServer

public class TimeServer {

    public static void main(String[] args) throws IOException {
        int port  = 8080;
        if (args != null && args.length >0){
            try{
                port = Integer.parseInt(args[0]);
            }catch (NumberFormatException e){

            }
        }

        MultiplexerTimeServer timeServer = new MultiplexerTimeServer(port);

        new Thread(timeServer).start();
    }
}

其中，我们创建了一个MultiplexerTimeServer的多路复用类，它是一个独立的线程，负责轮询多路复用器Selector，其代码如下：

public class MultiplexerTimeServer implements Runnable{

    private Selector selector;

    private ServerSocketChannel serverSocketChannel;

    private volatile boolean stop;

    public MultiplexerTimeServer(int port){
        try {
            selector = Selector.open();
            serverSocketChannel =  ServerSocketChannel.open();
            serverSocketChannel.configureBlocking(false);
            serverSocketChannel.socket().bind(new InetSocketAddress(port),1024);
            serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
        } catch (IOException e) {
            e.printStackTrace();
            System.exit(1);
        }
    }

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

    public void run() {
        while (!stop){
            try{
                selector.select(1000);
                Set<SelectionKey> selectionKeys = selector.selectedKeys();
                Iterator<SelectionKey> iterator = selectionKeys.iterator();
                SelectionKey key = null;
                while (iterator.hasNext()){
                    key = iterator.next();
                    iterator.remove();
                    try {
                        handleInput(key);
                    }catch (Exception e){
                        if (key != null){
                            key.cancel();
                            if (key.channel() != null){
                                key.channel().close();
                            }
                        }
                    }
                }
            } catch (Throwable e) {
                e.printStackTrace();
            }
        }
    }

    private void handleInput(SelectionKey key) throws IOException {
        if (key.isValid()){
            if (key.isAcceptable()){
                ServerSocketChannel ssc = (ServerSocketChannel)key.channel();
                SocketChannel sc = ssc.accept();
                sc.configureBlocking(false);
                sc.register(selector,SelectionKey.OP_READ);
            }
            if (key.isReadable()){
                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");
                    String curentTime = "QUERY TIME ORDER".equalsIgnoreCase(body)?new Date(
                            System.currentTimeMillis()
                    ).toString():"BAD ORDER";
                    doWrite(sc,curentTime);
                }else if(readBytes<0){
                    key.cancel();
                    sc.close();
                }else{

                }
            }
        }
    }

    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);
        }
    }
}

NIO客户端时序图

1. 打开SocketChannel，绑定客户端本地地址
2. 设置SocketChannel为非阻塞模式，同时设置客户端连接的TCP参数
3. 异步连接服务端
4. 判断是否连接成功，如果连接成功，则直接注册读状态未到多路复用器中。
5. 向Reactor线程的多路复用器注册OP_CONNECT状态位，监听服务端的TCP ACK应答。
6. 创建Reactor线程，创建多路复用器启动线程
7. 多路复用器在线程run方法的无限循环体中轮询准备就绪的Key
8. 接受connect事件进行处理
9. 判断连接成功，如果连接成功，注册读事件到多路复用器
10. 注册读事件到多路复用器
11. 异步读客户端请求到缓冲区
12. 对ByteBuffer进行编解码，如果有半包消息接受缓冲区Reset，继续读取后续的报文，将解码成功的消息封装成Task，投递到业务线程池中，进行业务逻辑编排。

NIO改造后 TimeClient

public class TimeClient {

    public static void main(String[] args) throws IOException {
        int port = 8080;
        if (args != null && args.length > 0) {
            try {
                port = Integer.parseInt(args[0]);
            } catch (NumberFormatException e) {

            }
        }
        new Thread(new TimeClientHandle("127.0.0.1",port)).start();
    }
}

与之前不同的地方在于通过创建TimeClientHandle线程来处理异步连接和读写操作 ,因此下面我们看看TimeClientHandle的实现。

public class TimeClientHandle implements Runnable{
    private String host;
    private int port;
    private Selector selector;
    private SocketChannel socketChannel;
    private volatile boolean stop;

    public TimeClientHandle(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);
        }
    }

    public void run() {
        try {
            doConnect();
        } catch (IOException e) {
            e.printStackTrace();
            System.exit(1);
        }
        while (!stop){
            try{
                selector.select(1000);
                Set<SelectionKey> selectionKeys = selector.selectedKeys();
                Iterator<SelectionKey> it = selectionKeys.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 (IOException e) {
                e.printStackTrace();
                System.exit(1);
            }
        }
    }

    private void handleInput(SelectionKey key) throws IOException {
        if (key.isValid()){
            SocketChannel sc = (SocketChannel) key.channel();
            if (key.isConnectable()){
                if (sc.finishConnect()){
                    sc.register(selector,SelectionKey.OP_READ);
                    doWrite(sc);
                }else{
                    System.exit(1);
                }
            }
            if (key.isReadable()){
                ByteBuffer readBuffer = ByteBuffer.allocate(1024);
                int readBytes = sc.read(readBuffer);
                if (readBytes > 0){
                    byte[] bytes = new byte[readBuffer.remaining()];
                    readBuffer.get(bytes);
                    String body = new String(bytes,"UTF-8");
                    System.out.println(body);
                    this.stop = true;
                }else if(readBytes < 0){
                    key.cancel();
                    sc.close();
                }else{

                }
            }
        }
    }

    private void doConnect() throws IOException {
        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[] bytes = "QUERY TIME ORDER".getBytes();
        ByteBuffer writeBuffer = ByteBuffer.allocate(bytes.length);
        writeBuffer.put(bytes);
        writeBuffer.flip();
        sc.write(writeBuffer);
        if (!writeBuffer.hasRemaining()){
            System.out.println("succeed");
        }
    }
}

来源：https://www.cnblogs.com/junjiang3/p/10164513.html