Is there a Java equivalent of GetCompressedFileSize?

Question

I am looking to get accurate (i.e. the real size on disk and not the normal size that includes all the 0's) measurements of sparse files in Java.

In C++ on Windows one would use GetCompressedFileSize. I have yet to come across how one would go about doing that in Java?

If there isn't a direct equivalent, how would I go about measuring the data within a sparse file, as opposed to the size including all of the zeros?

For clarification, I am look for this to run the sparse file measurements on both on Linux OS as well as Windows, however I don't mind coding two separate applications!

Hi Michael, I have edited my question to answer this. Thanks — J C, Feb 06 '13 at 18:01
possible duplicate of [Calling Win32 API method from Java](http://stackoverflow.com/questions/2389156/calling-win32-api-method-from-java) — Robᵩ, Feb 06 '13 at 18:07
I have added an answer for Linux, although i am not sure in it for all 100% — Michael, Feb 06 '13 at 18:12
@Robᵩ I do not think this is a duplicate as the edited question wants a solution for windows and linux, so it can't just call the Win32 function. — David Brown, Feb 06 '13 at 18:34

score 1 · Answer 1 · edited May 03 '21 at 10:40

If you are doing it on Windows alone, you can write it with Java Native Interface

class NativeInterface{
   public static native long GetCompressedFileSize(String filename);
}

and in C/C++ file:

extern "C"
JNIEXPORT jlong JNICALL Java_NativeInterface_GetCompressedFileSize
  (JNIEnv *env, jobject obj, jstring javaString)
{
    const char *nativeString = env->GetStringUTFChars(javaString, 0);
 
    char buffer[512];
    strcpy(buffer, nativeString);
    env->ReleaseStringUTFChars(javaString, nativeString);
    return (jlong) GetCompressedFileSize(buffer, NULL);
}

score 1 · Answer 2 · answered Jul 28 '18 at 12:39

If you want a pure Java solution you can try jnr-posix. Here's an example implementation

import jnr.posix.*;

final POSIX p = POSIXFactory.getPOSIX();
final int S_BLKSIZE = 512; // from sys/stat.h
final FileStat stat = p.stat("/path/to/file");
final long bytes = stat.blocks() * S_BLKSIZE;

However currently the function won't work for Windows. Until that's fixed you have to use platform-specific code like below

On Linux use the stat64 system call

The st_blocks field indicates the number of blocks allocated to the file, 512-byte units. (This may be smaller than st_size/512 when the file has holes.)
- You can also run the stat command. The number of allocated blocks can be seen in the Blocks field, or printed with the %b format specifier
- Or use du command (without --apparent-size option)
  --apparent-size
  - print apparent sizes, rather than disk usage; although the apparent size is usually smaller, it may be larger due to holes in ('sparse') files, internal fragmentation, indirect blocks, and the like

On Windows you can call the GetCompressedFileSize API

Alternatively you can also run fsutil file layout with admin rights to get detailed information about a file. Find the $DATA stream.

If you see Resident | No clusters allocated in the flags like this then it's a resident file and size on disk would be 0.

PS C:\Users>  fsutil file layout .\desktop.ini

********* File 0x000800000003dbde *********
File reference number   : 0x000800000003dbde
File attributes         : 0x00000026: Hidden | System | Archive
File entry flags        : 0x00000000
Link (ParentID: Name)   : 0x001f0000000238c8: HLINK Name   : \Users\desktop.ini
...
Stream                  : 0x080  ::$DATA
    Attributes          : 0x00000000: *NONE*
    Flags               : 0x0000000c: Resident | No clusters allocated
    Size                : 174
    Allocated Size      : 176

If you don't see the resident flag then check the Allocated Size field, it's the file's size on disk

PS D:\>  fsutil file layout .\nonresident.txt

********* File 0x000400000000084e *********
File reference number   : 0x000400000000084e
File attributes         : 0x00000020: Archive
File entry flags        : 0x00000000
Link (ParentID: Name)   : 0x0005000000000005: HLINK Name   : \nonresident.txt
...
Stream                  : 0x080  ::$DATA
    Attributes          : 0x00000000: *NONE*
    Flags               : 0x00000000: *NONE*
    Size                : 1,520
    Allocated Size      : 4,096
    Extents             : 1 Extents
                        : 1: VCN: 0 Clusters: 1 LCN: 1,497,204

For more information you can read the below questions

score 0 · Answer 3 · answered Feb 06 '13 at 18:10

0

Since an answer was given for windows. i will try to supply for Linux.

I am not sure, but i think it will do the trick (C++):

#include <linux/fs.h>
ioctl(file, BLKGETSIZE64, &file_size_in_bytes);

This can be loaded in the same way that was described in the @Aniket answer (JNI)

answered Feb 06 '13 at 18:10

Michael

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This isn't correct. [`GetCompressedFileSize` returns the real size on disk for compressed and sparse files](https://learn.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-getcompressedfilesizea) – phuclv Jul 13 '18 at 03:54

Is there a Java equivalent of GetCompressedFileSize?

3 Answers3

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