nio Write

ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
serverSocketChannel.configureBlocking(false);
serverSocketChannel.bind(new InetSocketAddress(“127.0.0.1”, 8080), 50);
Selector selector = Selector.open();
SelectionKey serverSocketKey = serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
while (true) {
System.out.println(“aaaa”);
int count = selector.select();
System.out.println(“select event count:” + count);;
Set selectionKeys = selector.selectedKeys();
Iterator iterator = selectionKeys.iterator();
while (iterator.hasNext()) {
System.out.println(“bbbbb”);
SelectionKey selectionKey = iterator.next();
// 有客户端请求建立连接
if (selectionKey.isAcceptable()) {
handleAccept(selectionKey);
iterator.remove();
}
// 有客户端发送数据
else if (selectionKey.isReadable()) {
handleRead(selectionKey);
iterator.remove();
}
// 可以向客户端发送数据
else if (selectionKey.isWritable()) {
handleWrite(selectionKey);
if (!isInterest(selectionKey, SelectionKey.OP_WRITE)) {
selectionKey.interestOps(selectionKey.interestOps() + SelectionKey.OP_WRITE);
}
selector.wakeup();
}

        }
    }
}

private static void handleAccept(SelectionKey selectionKey) throws IOException {
    ServerSocketChannel serverSocketChannel = (ServerSocketChannel) selectionKey.channel();
    SocketChannel socketChannel = serverSocketChannel.accept();
    if (Objects.nonNull(socketChannel)) {
        System.out.println("receive connection from client. client:{}"+ socketChannel.getRemoteAddress());
        // 设置客户端Channel为非阻塞模式，否则在执行socketChannel.read()时会阻塞
        socketChannel.configureBlocking(false);
        Selector selector = selectionKey.selector();
        socketChannel.register(selector, SelectionKey.OP_READ);
    }
}

private static void handleRead(SelectionKey selectionKey) throws IOException {
    SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
    ByteBuffer readBuffer = ByteBuffer.allocate(32);
    int length = 0;
    while (length < 2) {
        length += socketChannel.read(readBuffer);
    }
    System.out.println("receive message from client. client:{} message length:{}");

    ByteBuffer writeBuffer = ByteBuffer.allocate(readBuffer.position());
    readBuffer.flip();
    writeBuffer.put(readBuffer);
    // 读完数据后，为 SelectionKey 注册可写事件
    if (!isInterest(selectionKey, SelectionKey.OP_WRITE)) {
        selectionKey.interestOps(selectionKey.interestOps() + SelectionKey.OP_WRITE);
    }
    writeBuffer.flip();
    selectionKey.attach(writeBuffer);
}

// 服务端可能是为每个Channel维护一块缓冲区，当向某个Channel写数据时缓冲区满了，还可以向其他Channel写数据
private static void handleWrite(SelectionKey selectionKey) throws IOException {
    SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
    ByteBuffer writeBuffer = (ByteBuffer) selectionKey.attachment();
    int writeLength = socketChannel.write(writeBuffer);
    if (!writeBuffer.hasRemaining()) {
        // 写完数据后，要把写事件取消，否则当写缓冲区有剩余空间时，会一直触发写事件
        selectionKey.interestOps(selectionKey.interestOps() - SelectionKey.OP_WRITE);
        // socketChannel.shutdownOutput(); // channel调用shutdownOutput()后，会停止触发写事件
    }
}

// 判断 SelectionKey 对某个事件是否感兴趣
private static boolean isInterest(SelectionKey selectionKey, int event) {
    int interestSet = selectionKey.interestOps();
    boolean isInterest = (interestSet & event) == event;
    return isInterest;
}