问Java高负载NIO TCP服务器

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public class EchoServer {

private static final int BUFFER_SIZE = 1024;
private final static int DEFAULT_PORT = 9090;

// The buffer into which we'll read data when it's available
private ByteBuffer readBuffer = ByteBuffer.allocate(BUFFER_SIZE);

private InetAddress hostAddress = null;

private int port;
private Selector selector;

private long loopTime;
private long numMessages = 0;

public EchoServer() throws IOException {
    this(DEFAULT_PORT);
}

public EchoServer(int port) throws IOException {
    this.port = port;
    selector = initSelector();
    loop();
}

private void loop() {
    while (true) {
        try{
            selector.select();
            Iterator<SelectionKey> selectedKeys = selector.selectedKeys().iterator();
            while (selectedKeys.hasNext()) {
                SelectionKey key = selectedKeys.next();
                selectedKeys.remove();

                if (!key.isValid()) {
                    continue;
                }

                // Check what event is available and deal with it
                if (key.isAcceptable()) {
                    accept(key);
                } else if (key.isReadable()) {
                    read(key);
                } else if (key.isWritable()) {
                    write(key);
                }
            }

        } catch (Exception e) {
            e.printStackTrace();
            System.exit(1);
        }
    }
}

private void accept(SelectionKey key) throws IOException {
    ServerSocketChannel serverSocketChannel = (ServerSocketChannel) key.channel();

    SocketChannel socketChannel = serverSocketChannel.accept();
    socketChannel.configureBlocking(false);
    socketChannel.setOption(StandardSocketOptions.SO_KEEPALIVE, true);
    socketChannel.setOption(StandardSocketOptions.TCP_NODELAY, true);
    socketChannel.register(selector, SelectionKey.OP_READ);

    System.out.println("Client is connected");
}

private void read(SelectionKey key) throws IOException {
    SocketChannel socketChannel = (SocketChannel) key.channel();

    // Clear out our read buffer so it's ready for new data
    readBuffer.clear();

    // Attempt to read off the channel
    int numRead;
    try {
        numRead = socketChannel.read(readBuffer);
    } catch (IOException e) {
        key.cancel();
        socketChannel.close();

        System.out.println("Forceful shutdown");
        return;
    }

    if (numRead == -1) {
        System.out.println("Graceful shutdown");
        key.channel().close();
        key.cancel();

        return;
    }

    socketChannel.register(selector, SelectionKey.OP_WRITE);

    numMessages++;
    if (numMessages%100000 == 0) {
        long elapsed = System.currentTimeMillis() - loopTime;
        loopTime = System.currentTimeMillis();
        System.out.println(elapsed);
    }
}

private void write(SelectionKey key) throws IOException {
    SocketChannel socketChannel = (SocketChannel) key.channel();
    ByteBuffer dummyResponse = ByteBuffer.wrap("ok".getBytes("UTF-8"));

    socketChannel.write(dummyResponse);
    if (dummyResponse.remaining() > 0) {
        System.err.print("Filled UP");
    }

    key.interestOps(SelectionKey.OP_READ);
}

private Selector initSelector() throws IOException {
    Selector socketSelector = SelectorProvider.provider().openSelector();

    ServerSocketChannel serverChannel = ServerSocketChannel.open();
    serverChannel.configureBlocking(false);

    InetSocketAddress isa = new InetSocketAddress(hostAddress, port);
    serverChannel.socket().bind(isa);
    serverChannel.register(socketSelector, SelectionKey.OP_ACCEPT);
    return socketSelector;
}

public static void main(String[] args) throws IOException {
    System.out.println("Starting echo server");
    new EchoServer();
}
}