Three components of NIO foundation

I. Channel

Channel is a bit similar to stream, it is a bidirectional channel for reading and writing data. It can read data from channel into buffer, or write buffer data into channel, and the previous stream orWhether it is input or output, channel is a lower level than stream.
Channels are typed, a string channel can only store string type data.
You can use Buffer as a container to take data out or add data to Channel.If Channel is a water tank, then Buffer is a scoop of water.

Common Channels are

• FileChannel
• DatagramChannel
• SocketChannel
• ServerSocketChannel

Second, Buffer

buffer is used to buffer read and write data. Use buffer to read or write data to channel. The buffer is the same as the array used to read and write files. Common buffers include

• ByteBuffer
  • MappedByteBuffer
  • DirectByteBuffer
  • HeapByteBuffer
• ShortBuffer
• IntBuffer
• LongBuffer
• FloatBuffer
• DoubleBuffer
• CharBuffer

Three, Selector

Selector is generally called a selector, which can also be translated as a multiplexer. It is one of the core components of Java NIO and is used to check whether the state of one or more NIO Channels is in a readable and readable state.Writing
can implement a single thread to manage multiple channels, which avoids the overhead of thread context switching compared to using multiple threads.
The role of the selector is to cooperate with a thread to manage multiple channels and obtain the events that occur on these channels. These channels work in non-blocking mode and will not let threads hang on a channel.It is suitable for scenarios with a large number of connections but low traffic (low traffic)
Data reading occurs in the channel. In a single thread, the reading of multiple channels is blocked, and one channel is waiting for the client to read.During the process, other channels will be blocked. If multi-threading is used, it will be a challenge to system performance.

And the selector can also perform multiple operations in a single threadChannel is managed. By means of channel event monitoring, calling selector's select() will block until the channel has read and write ready events. When these events occur, the select method will return these events to thread for processing.
Selector maintains a set of registered Channels, and this registration relationship is encapsulated in SelectionKey.The selector can customize which events to listen to. The types of events that can be bound are:
The types of events that can be bound can be

• connect - fired when the client connects successfully
• accept - fires when the server side successfully accepts the connection
• read - Triggered when the data can be read, there are cases where the data cannot be read temporarily due to weak receiving ability
• write - Triggered when the data can be written out, there are cases where the data cannot be written temporarily due to the weak sending ability