One 、 Channel

channel A little similar to stream, It is the of reading and writing data Two-way channel , It can be downloaded from channel Read data into buffer, Can also be buffer Data written to channel, And before stream Or enter , Or output ,channel Than stream It's even lower .
channel There are types of , One string Of channel Only store string Type data .
Can pass Buffer As a container , Go to Channel Take out data or add data . If Channel It's a water tank , that Buffer It's the ladle that draws water .

common Channel Yes

• FileChannel
• DatagramChannel
• SocketChannel
• ServerSocketChannel

Two 、Buffer

buffer Is used to buffer read-write data , Use buffer To read or write channel The data of ,buffer Just like the array used when reading and writing files , common buffer Yes

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

3、 ... and 、 Selector

Selector Commonly referred to as selectors , It can also be translated into multiplexer , It is Java NIO One of the core components , Used to check one or more NIO Channel（ passageway ） Whether the state of is readable 、 Can write
You can manage multiple threads with a single thread channels, Instead of using multiple threads , Avoid the overhead of thread context switching .
selector The function of is to cooperate with one thread to manage multiple channel, Get these channel What happened on , these channel Working in non blocking mode , It won't let the thread hang in a channel On . Suitable for a large number of connections , But low traffic scenarios （low traffic）
channel Data reading will appear in , In a single thread , Multiple channel All reads are blocked , One channel While waiting for the client to read , It's blocking other channel, If you use multithreading , It is a challenge to system performance .

and selector, It can be applied to multiple threads in a single thread channel Conduct management , adopt channel The way events are monitored , call selector Of select() Will block until channel A read-write ready event has occurred , These events happened ,select Method will return these events to thread To deal with it .
Selector Maintain registered Channel aggregate , And this registration relationship is encapsulated in SelectionKey in .selector You can customize and choose to listen to those events , The event types that can be bound are ：
The bound event types can be

• connect - Triggered when the client connection is successful
• accept - Triggered when the server successfully accepts the connection
• read - Triggered when data can be read in , Yes, because the reception capacity is weak , The data cannot be read temporarily
• write - Triggered when data can be written out , Yes, because the sending ability is weak , Data cannot be written out temporarily