What is the fastest method for reading from a text file in Java?

Question

I currently use:

BufferedReader input = new BufferedReader(new FileReader("filename"));

Is there a faster way?

Answer 1

Look into java.nio.channels.FileChannel.

Answer 2

Have you benchmarked your other options? I imagine that not using a BufferedReader may be faster in some cases - like extremely small files. I would recommend that you at the very least do some small benchmarks and find the fastest implementation that works with your typical use cases.

Answer 3

While what you've got isn't necessarily the absolute fastest, it's simple. In fact, I wouldn't use quite that form - I'd use something which allows me to specify a charset, e.g.

// Why is there no method to give this guaranteed charset
// without "risk" of exceptions? Grr.
Charset utf8 = Charset.forName("UTF-8");     
BufferedReader input = new BufferedReader(
                           new InputStreamReader(
                               new InputStream("filename"),
                               utf8));

You can probably make it go faster using NIO, but I wouldn't until I'd seen an actual problem. If you see a problem, but you're doing other things with the data, make sure they're not the problem first: write a program to just read the text of the file. Don't forget to do whatever it takes on your box to clear file system caches between runs though...

Answer 4

Depends on what you want to read. The complete file, or from a specific location, do you need to able to seatch through it, or do you want to read the complete text in one go?

Answer 5

If it's /fast/ you want, keep the character data in encoded form (and I don't mean UTF-16). Although disc I/O is generally slow (unless it's cached), decoding and keeping twice the data can also be a problem. Although the fastest to load is probably through java.nio.channels.FileChannel.map(MapMode.READ_ONLY, ...), that has severe problems with deallocation.

Usual caveats apply.