Memory-mapped files in Java

Question

I\'ve been trying to write some very fast Java code that has to do a lot of I/O. I\'m using a memory mapped file that returns a ByteBuffer:

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Answer 1

Its always good not to reinvent the wheels. Apache has provided a beautiful library for performing I/O operations. Take a look at http://commons.apache.org/io/description.html

Here's the scenario it serves. Suppose you have some data that you'd prefer to keep in memory, but you don't know ahead of time how much data there is going to be. If there's too much, you want to write it to disk instead of hogging memory, but you don't want to write to disk until you need to, because disk is slow and is a resource that needs tracking for cleanup.

So you create a temporary buffer and start writing to that. If / when you reach the threshold for what you want to keep in memory, you'll need to create a file, write out what's in the buffer to that file, and write all subsequent data to the file instead of the buffer.

That's what DeferredOutputStream does for you. It hides all the messing around at the point of switch-over. All you need to do is create the deferred stream in the first place, configure the threshold, and then just write away to your heart's content.

EDIT: I just did a small re-search using google and found this link: http://lists.apple.com/archives/java-dev/2004/Apr/msg00086.html (Lightning fast file read/write). Very impressive.