java - Fastest way to write to file?

Question

I made a method that takes a File and a String. It replaces the file with a new file with that string as its contents.

This is what I made:

public static void Save(File file, String textToSave) {

    file.delete();
    try {
        BufferedWriter out = new BufferedWriter(new FileWriter(file));
        out.write(textToSave);
        out.close();
    } catch (IOException e) {
    }
}

However it is painfully slow. It sometimes takes over a minute.

How can I write large files with tens of thousands to maybe up to a million characters in them?

Answer 1

Make sure you allocate a large enough buffer:

BufferedWriter out = new BufferedWriter(new FileWriter(file), 32768);

What sort of OS are you running on? That can make a big difference too. However, taking a minute to write out a file of less-than-enormous size sounds like a system problem. On Linux or other *ix systems, you can use things like strace to see if the JVM is making lots of unnecessary system calls. (A very long time ago, Java I/O was pretty dumb and would make insane numbers of low-level write() system calls if you weren't careful, but when I say "a long time ago" I mean 1998 or so.)

edit — note that the situation of a Java program writing a simple file in a simple way, and yet being really slow, is an inherently odd one. Can you tell if the CPU is heavily loaded while the file is being written? It shouldn't be; there should be almost no CPU load from such a thing.