Format file size as MB, GB, etc

Question

I need to display a file size as a string using sensible units.

For example,

1L ==> "1 B";
1024L ==> "1 KB";
2537253L ==> "2.3 MB"

etc.

I found this previous answer, which I didn't find satisfactory.

I have come up with my own solution which has similar shortcomings:

private static final long K = 1024;
private static final long M = K * K;
private static final long G = M * K;
private static final long T = G * K;

public static String convertToStringRepresentation(final long value){
    final long[] dividers = new long[] { T, G, M, K, 1 };
    final String[] units = new String[] { "TB", "GB", "MB", "KB", "B" };
    if(value < 1)
        throw new IllegalArgumentException("Invalid file size: " + value);
    String result = null;
    for(int i = 0; i < dividers.length; i++){
        final long divider = dividers[i];
        if(value >= divider){
            result = format(value, divider, units[i]);
            break;
        }
    }
    return result;
}

private static String format(final long value,
    final long divider,
    final String unit){
    final double result =
        divider > 1 ? (double) value / (double) divider : (double) value;
    return String.format("%.1f %s", Double.valueOf(result), unit);
}

The main problem is my limited knowledge of Decimalformat and / or String.format. I would like 1024L, 1025L, etc. to map to 1 KB rather than 1.0 KB.

So, two possibilities:

1. I would prefer a good out-of-the-box solution in a public library like Apache Commons or Google Guava.
2. If there isn't, how can I get rid of the '.0' part (without resorting to string replacement and regex, I can do that myself)?

Solution 1

public static String readableFileSize(long size) {
    if(size <= 0) return "0";
    final String[] units = new String[] { "B", "kB", "MB", "GB", "TB" };
    int digitGroups = (int) (Math.log10(size)/Math.log10(1024));
    return new DecimalFormat("#,##0.#").format(size/Math.pow(1024, digitGroups)) + " " + units[digitGroups];
}

This will work up to 1000 TB.... and the program is short!

Solution 2

You'll probably have more luck with java.text.DecimalFormat. This code should probably do it (just winging it though...)

new DecimalFormat("#,##0.#").format(value) + " " + unit

Solution 3

It is surprising for me, but a loop-based algorithm is about 10% faster.

public static String toNumInUnits(long bytes) {
    int u = 0;
    for ( ; bytes > 1024*1024; bytes >>= 10) {
        u++;
    }
    if (bytes > 1024)
        u++;
    return String.format("%.1f %cB", bytes/1024f, " kMGTPE".charAt(u));
}

Comments

[Stefan Hoth]

This should be the "correct" answer as it takes the unit into account.

[ruslanys]

Agree, should be the correct answer. Look here for an even better output.

[Joe]

final String[] units = new String[] { "B", "KB", "MB", "GB", "TB", "EB" }; // now it works up to Long.MAX_VALUE!

[Mr Ed]

To comply with international standards: final String[] units = new String[] { "B", "KB", "MB", "GB", "TB", "PB", "EB" }; /* used with 1000 * / final String[] units = new String[] { "Bi", "KiB", "MiB", "GiB", "TiB", "PiB", "EiB" }; /* used with 1024 */ See: physics.nist.gov/cuu/Units/binary.html

[nefo_x]

and reverse function?...

[Mr Ed]

nefo_x: The reverse function is impossible because you lose precision. If you wanted an approximation, you can parse the string to get the number part, then multiply that number by the factor which corresponds with the units string, i.e. "KB" would use the factor 1000.

[Evgeni Sergeev]

Everything is loop based at the bottom.

[Willem Van Onsem]

A small comment: "kilo" is expressed with a lowercase 'k' and not an uppercase 'K'.

[dbro]

Might want to return "0 B" or otherwise include units in zero case.

[user4955663]

Joe: Petabyte comes before Exabyte and don't forget these: Zettabyte, Yottabyte, so the complete list is: "B", "kB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB" See: en.wikipedia.org/wiki/Yottabyte Yes I know ZB and YB are not needed today, but maybe in the future...;)

[Himanshu Mori]

"This will work up to 1000 TB" yes it is not working after this limit

[Chop]

Maybe using .format(size/Math.pow(1024, Math.min(digitGroups, units.length))) could fix the problem of filesizes above 1000TB?

[Kamil Ibadov]

Perfect, Thank you!

[Erik B]

@WillemVanOnsem kilo is 1000, this is 1024

[Willem Van Onsem]

@ErikB: I did not post this, I only replaced KB with kB :)

[android developer]

Just a tip for Android developers : To show the file size in a nice readable way on Android, you can use Formatter.formatShortFileSize(context,file.length())

[user4955663]

See scala solution ported from this code: stackoverflow.com/questions/35609587/… Also support for ZB and YB.

[Anupreet Kaur]

Getting crash sometimes. Usually when its in KB java.lang.NumberFormatException: For input string: "1,010.3" @WillemVanOnsem Can you please help me

[Denis K]

This DecimalFormat will produce different results based on Locale. I added this to have consistency regardless of environment: DecimalFormatSymbols symbols = new DecimalFormatSymbols(Locale.US); DecimalFormat formatter = new DecimalFormat("#,##0.##", symbols);

[Peter Mortensen]

Does it work as required?

[Peter Mortensen]

@Evgeni Sergeev: What do you mean? Can you elaborate?

[Robert Watkins]

Strangely enough, after ten years, I haven't gone back and tested this. Try it yourself and see...

[xonya]

Warning: this doesn't work for bytes <= 1024 (result is always 0.0 B). You need to add if (bytes <= 1024) { return String.format("%.1f B", (float) bytes); } at the beginning of the method.