小白也可以学会的Java NIO的Write事件

//打开选择器
Selector selector = Selector.open();
//打开通到
ServerSocketChannel socketChannel = ServerSocketChannel.open();
//配置非阻塞模型
socketChannel.configureBlocking(false);
//绑定端口
socketChannel.bind(new InetSocketAddress(8080));
//注册事件，OP_ACCEPT只适用于ServerSocketChannel 
socketChannel.register(selector, SelectionKey.OP_ACCEPT);
while (true) {
    selector.select();
    Set<SelectionKey> selectionKeys = selector.selectedKeys();
    Iterator<SelectionKey> iter = selectionKeys.iterator();
    while(iter.hasNext()) {
        SelectionKey key = iter.next();
        if(key.isAcceptable()) {
            SocketChannel channel = ((ServerSocketChannel)key.channel()).accept();
            channel.configureBlocking(false);
            channel.register(selector,SelectionKey.OP_READ);
        }
        
        if(key.isWritable()) {
        }
        
        if(key.isReadable()) {
            SocketChannel channel = (SocketChannel) key.channel();
            ByteBuffer readBuffer = ByteBuffer.allocate(1024);
            channel.read(readBuffer);
            readBuffer.flip();
            // handler Buffer
            // 一般是响应客户端的数据
            // 直接是write写不就完事了嘛，为啥需要write事件？
            // channel.write(...)
        }
        iter.remove();
    }
}

// 200M的Buffer
ByteBuffer buffer = .... 

while(buffer.hasRemaining()) {
    // 该方法只会写入小于socket's output buffer空闲区域的任何字节数
    // 并返回写入的字节数，可能是0字节
    channel.write(buffer);
}

if(key.isReadable()) {
	// 200M Buffer
    ByteBuffer buffer = .... 
    // 注册写事件
    key.interestOps(key.interestOps() | SelectionKey.OP_WRITE);
    // 绑定Buffer
    key.attach(buffer);
}
// 可写分支
if(key.isWritable()) {
    ByteBuffer buffer = (ByteBuffer) key.attachment();
    SocketChannel channel = (SocketChannel) key.channel();
    if (buffer.hasRemaining()) {
        channel.write(buffer)
    } else {
        // 发送完了就取消写事件，否则下次还会进入写事件分支（因为只要还可写，就会进入）
        key.interestOps(key.interestOps() & ~SelectionKey.OP_WRITE);
    }
}

// 打开选择器
Selector selector = Selector.open();
// 打开通道
SocketChannel socketChannel = SocketChannel.open();
// 配置非阻塞模型
socketChannel.configureBlocking(false);
// 连接Server
socketChannel.connect(new InetSocketAddress("127.0.0.1",8080));
// 注册事件
socketChannel.register(selector, SelectionKey.OP_CONNECT | SelectionKey.OP_READ);
// 循环处理
while (true) {
    selector.select();
    Set<SelectionKey> keys = selector.selectedKeys();
    Iterator<SelectionKey> iter = keys.iterator();
    while(iter.hasNext()) {
        SelectionKey key = iter.next();
        if(key.isConnectable()) {
            // 连接建立或者连接建立不成功
            SocketChannel channel = (SocketChannel) key.channel();
            // 完成连接建立
            if(channel.finishConnect()) {
                
            }
        }
        
        if(key.isReadable()) {
            SocketChannel channel = (SocketChannel) key.channel();
            ByteBuffer buffer = ByteBuffer.allocate(500 * 1024 * 1024);
            buffer.clear();
            channel.read(buffer);
            // buffer Handler
        }
        iter.remove();
    }
}