Advantages of Java NIO in blocking mode versus traditional I/O?
I have pretty much already decided not to use asynchronous, non-blocking Java NIO. The complexity versus benefit is very questionable in general, and I think it's not worth it in this project particularly.
But most of what I read about NIO, and comparisons with older java.io.* focuses on non-blocking, asynchronous NIO versus thread-per-connection synchronous I/O using java.io.*. However, NIO can be used in synchronous, blocking, thread-per-connection mode, which is rarely discussed it seems.
Here's the question: Is there any performance advantage of synchronous, blocking NIO versus traditional synchronous, blocking I/O (java.io.*)? Both would be thread-per-connection. How does the complexity compare?
Note that this is a general question, but at the moment I am primarily concerned with TCP socket communication.
Answer
An advantage of NIO over "traditional" IO is that NIO can use direct buffers that allow the OS to use DMA for some operations (e.g. reading from a network connection directly into a memory-mapped file) and thereby avoid copying data to intermediate buffers.
If you're moving large amounts of data in a scenario where this technique does avoid copy operations that would otherwise be performed, this can have a big impact on performance.