最快的方式写入文件？ [英] Fastest way to write to file?

问题描述

我做了一个方法，它需要一个 File 和一个 String 。它用一个新的文件替换为该文件的内容。

这是我做的：

  public static void Save（File file，String textToSave）{
 
 file.delete（）; 
尝试{
 BufferedWriter out = new BufferedWriter（new FileWriter（file））; 
 out.write（textToSave）; 
 out.close（）; 
} catch（IOException e）{
} 
} 
  

然而，这是痛苦的缓慢。有时需要花费一分钟的时间。

如何编写数以万计的大型文件，其中可能包含多达一百万个字符？

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

你在运行什么样的操作系统？这也可以造成很大的不同。然而，用一个分钟来写出一个尺寸不太大的文件听起来像是一个系统问题。在Linux或其他* ix系统上，可以使用 strace 之类的东西来查看JVM是否进行了大量不必要的系统调用。 （很久以前，Java I / O很愚蠢，如果你不小心的话，会造成疯狂的低层次的 write（）系统调用，但是当我说很久以前我的意思是1998年左右。）

edit —请注意，Java程序以简单的方式编写一个简单的文件，但实际上很慢的情况本质上是一个奇怪的问题。你可以告诉CPU在文件写入过程中是否负载过重吗？它不应该是;应该几乎没有来自这样的事情的CPU负载。

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?

解决方案

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.

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