NIO（二）

TimeClient序列图

TimeClient序列图

TimeClient

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

/**
 * Created by liqiushi on 2017/12/12.
 */
public class TimeClient implements Runnable {

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

    public TimeClient(String host, int port) {
        this.host = host == null ? "127.0.0.1" : host;
        this.port = port;
        try {
            selector = selector.open();
            socketChannel = SocketChannel.open();

            //channel要设置成非阻塞
            socketChannel.configureBlocking(false);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void run() {
        try {
            doconnect();
        } catch (IOException e) {
            e.printStackTrace();
        }
        while (!stop) {
            try {
                selector.select(1000);
                Set selectedKeys = selector.selectedKeys();
                Iterator iterator = selectedKeys.iterator();
                while (iterator.hasNext()) {
                    SelectionKey selectionKey = iterator.next();
                    iterator.remove();
                    handleInput(selectionKey);
                }
            } catch (IOException e) {
                e.printStackTrace();
                System.exit(1);
            }
        }
        if (selector != null) {
            try {
                selector.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    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 handleInput(SelectionKey key) throws IOException {
        if (key.isValid()) {
            SocketChannel socketChannel = (SocketChannel) key.channel();
            if (key.isConnectable()) {
                if (socketChannel.finishConnect()) {
                    try {
                        socketChannel.register(selector, SelectionKey.OP_READ);
                        dowrite(socketChannel);
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                } else {
                    System.exit(1);
                }
            }
            if (key.isReadable()) {
                ByteBuffer readBuffer = ByteBuffer.allocate(1024);
                int readBytes = socketChannel.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 : " + body);
                    this.stop = true;
                } else if (readBytes < 0) {
                    //对端链路关闭
                    key.cancel();
                    socketChannel.close();
                }
            }
        }
    }

    private void dowrite(SocketChannel socketChannel) throws IOException {
        ByteBuffer writeBuffer = ByteBuffer.allocate(1024);
        String request = "QUERY TIME ORDER";
        byte[] bytes = request.getBytes();
        writeBuffer.put(bytes);
        writeBuffer.flip();
        socketChannel.write(writeBuffer);

        if (!writeBuffer.hasRemaining()) {
            System.out.println("Send order 2 server succeed.");
        }
    }

    public static void main(String[] args) {
        TimeClient timeClient = new TimeClient("127.0.0.1", 8001);
        new Thread(timeClient).start();
    }
}

疑问

isConnectable()和finishConnect()

if(key.isConnectable()){
            try {
                socketChannel.finishConnect();
                socketChannel.register(selector, SelectionKey.OP_READ);
            } catch (IOException e) {
                e.printStackTrace();
            }
}

在非阻塞模式下，SocketChannel的connect()会直接返回，不会由于io出错或直到连接成功才返回（阻塞情况下），而isConnectable()代表可以连接，接收到了服务端的SYN-ACK，属于第二次握手，此时正处于连接中，需要调用finishConnect()对连接进行确认。