Reference: https://medium.com/coderscorner/tale-of-client-server-and-socket-a6ef54a74763
Reference: https://www.amazon.com/Java-Nio-Ron-Hitchens/dp/0596002882

• please refer firstly https://github.com/mtumilowicz/java12-io-socket-client-server-workshop
  • the task is to rewrite SingleThreadedServerAnswer and ClientConnectionAnswer using NIO
• the main goal of this project is to show how to implement blocking server using java NIO
• in the workshop we will try to fix failing tests from test/workshop package by following steps and hints in java/workshop package
• answers: java/answers package

• Java NIO - Java New IO (not Java Non-blocking IO)
• channels are a new, first-class Java I/O paradigm
• channel is a conduit that transports data efficiently between byte buffers and the entity on the other end of the channel
  • you can think of the buffer as a temporary storage place
  • channel can be viewed as an endpoint for communication
    • for example if we take SocketChannel class, it reads from and writes to TCP sockets
    • data must be encoded in ByteBuffer objects for reading and writing
• channel implementations vary radically between operating systems
• I/O falls into two categories: file I/O and stream I/O
  • so there are two types of channels: file and socket
• socket channels are blocking by default
• socket channels can operate in nonblocking mode and are selectable (will be discussed in details in the other workshops)
• a good metaphor for a channel is a pneumatic tube, the type used at drive-up bank-teller windows
  • your paycheck would be the information you're sending
  • the carrier would be like a buffer
  • you fill the buffer (place your paycheck in the carrier), "write" the buffer to the channel (drop the carrier into the tube)
  • the payload is carried to the I/O service (bank teller) on the other end of the channel
  • the response would be the teller filling the buffer (placing your receipt in the carrier) and starting a channel transfer in the opposite direction (dropping the carrier back into the tube)
  • the carrier arrives on your end of the channel (a filled buffer is ready for you to examine)
  • you then flip the buffer (open the lid) and drain it (remove your receipt)
  • you drive away and the next object (bank customer) is ready to repeat the process using the same carrier (Buffer) and tube (Channel) objects
• vs io.sockets
  • in NIO based systems, instead of writing data onto output streams and reading data from input streams, we read and write data from buffers
  • instead of asking for socket’s input and output streams, we are going to write data to the channel itself
• SocketChannel.socket() - retrieves a socket associated with this channel

• SocketChannel - client side of the connection (~ Socket if blocking)
• ServerSocketChannel - server side of the connection (~ ServerSocket if blocking)