Java NIO Fundamentals

Basic Concepts

1. Channel & Buffer: data is always read from channel to buffer, or writtern from buffer to channel

2. Non-blocking IO: non-blocking while read and write data

3. Selector: A single thread monitor multiple channels for data

http://tutorials.jenkov.com/java-nio/index.html

Channel & Buffer

Selector

Single thread using just one selector can handle many connections open (channels), but low traffic on each connection (why low traffic?)

1. POSA2 Selector Pattern

2. Why should low traffic is assumption of channel is low traffic?

3. What is better way to handle the heavy traffic application?

4. Is channel also at the same thread of selector?

To use a selector, register a channel with it

Channels

1. FileChannel <=> Files

2. DatagramChannel <=> UDP

3. SocketChannel <=> TCP

4. ServerSocketChannel, listen for incoming TCP connections, like a web server. For each connection, a SocketChannel is created

Buffer

Four steps using buffer:

1. Write data into buffer

2. Call buffer.flip()  // filp switch from writting mode to reading modepos

3. Read data out of buffer

4. Call buffer.clear() or buffer.compact() // once all data have read all the data, need to clear the buffer, to make it ready for writing again

capacity & position & limit

capacity: the fixed memory block for buffer

position and limit are depends on which mode (the writing mode or reading mode?)

References:

http://tutorials.jenkov.com/java-nio/non-blocking-server.html#non-blocking-server-github-repository

http://www.drdobbs.com/jvm/high-performance-io-with-java-nio/184406242