How to identify a zip file in java?

Question

I want to identify my archive whether it is zip or rar. But the problem I get runtime error before I can validate my file. I want to create custom notification:

public class ZipValidator {
  public void validate(Path pathToFile) throws IOException {
    try {
      ZipFile zipFile = new ZipFile(pathToFile.toFile());
      String zipname = zipFile.getName();
    } catch (InvalidZipException e) {
      throw new InvalidZipException("Not a zip file");
    }
  }
}

At the moment I have runtime error:

java.util.zip.ZipException: error in opening zip file

Get the file name. split the file name with . and get extension. Check whether extension is rar or zip . — Ravindra babu, Nov 26 '15 at 09:13
@Ravindrababu - and What is stoppning one from simply changing the extension of a non zip file to zip or rar? — Cyclonecode, Dec 01 '17 at 14:42

bratkartoffel · Answer 1 · 2015-11-26T09:48:18.763

I'd suggest to open a plain InputStream an reading the first few bytes (magic bytes) and not to rely on the file extension as this can be easily spoofed. Also, you can omit the overhead creating and parsing the files.

For RAR the first bytes should be 52 61 72 21 1A 07.

For ZIP it should be one of:

50 4B 03 04
50 4B 05 06 (empty archive)
50 4B 07 08 (spanned archive).

Source: https://en.wikipedia.org/wiki/List_of_file_signatures

Another point, just looked at your code:

Why do you catch die InvalidZipException, throw it away and construct a new one? This way you lose all the information from the original exception, making it hard to debug and understand what exactly went wrong. Either don't catch it at all or, if you have to wrap it, do it right:

} catch (InvalidZipException e) {
  throw new InvalidZipException("Not a zip file", e);
}

score 20 · Answer 2 · edited Apr 16 '19 at 12:06

20

Merging the answers of nanda & bratkartoffel.

private static boolean isArchive(File f) {
    int fileSignature = 0;
    try (RandomAccessFile raf = new RandomAccessFile(f, "r")) {
        fileSignature = raf.readInt();
    } catch (IOException e) {
        // handle if you like
    }
    return fileSignature == 0x504B0304 || fileSignature == 0x504B0506 || fileSignature == 0x504B0708;
}

edited Apr 16 '19 at 12:06

wcmatthysen

445
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19

answered Dec 01 '17 at 14:26

Fabian Braun

3,612
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Better use InputStream as it's handling a more general input, no? – android developer Feb 03 '21 at 20:13
This does not work for me. It evaluates a .docx file to true – Thanasis Namikazee Apr 26 '23 at 19:35
@ThanasisNamikazee a docx file is, in fact, a zip file with a changed file extension – Fabian Braun Apr 27 '23 at 21:00
@FabianBraun its a fact I did not know about. So in reality this code works as expected. – Thanasis Namikazee Apr 30 '23 at 19:23

score 4 · Answer 3 · answered Nov 26 '15 at 09:28

Exception is thrown in line

ZipFile zipFile = new ZipFile(pathToFile.toFile());

That's because if a non-ZipFile is given as parameter for the ZipFileconstructor the ZipException is thrown. So you have to check before generating a new ZipFile Object if your file path points to a correct ZipFile. One solution might be to check the extension of the file path like so

 PathMatcher matcher = FileSystems.getDefault().getPathMatcher("glob:*.zip");
 boolean extensionCorrect = matcher.matches(path);

This does not work. For example I am using a .docx file and does not throw exception — Thanasis Namikazee, Apr 26 '23 at 19:33

score 4 · Answer 4 · edited Nov 26 '15 at 09:39

4

RandomAccessFile raf = new RandomAccessFile(f, "r");

long n = raf.readInt();

raf.close();

if (n == 0x504B0304)

    System.out.println("Should be a zip file");

else

    System.out.println("Not a zip file");

You can see it in the following link. http://www.coderanch.com/t/381509/java/java/check-file-zip-file-java

edited Nov 26 '15 at 09:39

Abhinav Singh Maurya

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answered Nov 26 '15 at 09:30

nanda

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2

Partly correct, there can be 3 different signatures, not just one. – bratkartoffel Nov 26 '15 at 09:45

score 0 · Answer 5 · answered Apr 11 '22 at 20:18

Apache Tika was created to extract metadata from files, but one of its side benefits is it will determine a file's media-type by either its magic bytes and/or the files extension.

public String detect(InputStream stream, String name) throws IOException

Detects the media type of the given document. The type detection is based on the content of the given document stream and the name of the document.

score 0 · Answer 6 · answered Aug 26 '23 at 19:41

I resolved it using Apache Tika (here for gzip):

final MimeTypes mimeTypes = MimeTypes.getDefaultMimeTypes(ClassLoader.getSystemClassLoader());
boolean isCompressed = mimeTypes.forName("application/gzip").matches(
        FileUtils.readFileToByteArray(FileUtils.getFile(filepath))
);

Remark: the library use the magic bytes, so it should be possible to read only some start bytes of the file instead of using FileUtils.getFile().

How to identify a zip file in java?

6 Answers6

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