Is there a way to check if a file is a zip file in java?

[ken carlino]

Is there a way to check if a file is a zip file in java?
Checking file extension is one way, but is there a better way?

Thank you.

[Prabhu Venkatachalam]

Use file filters. There is File utility in Apache common.io package.

URL

For example,

IOFileFilter suffixFilter = FileFilterUtils.suffixFileFilter("zip");

[Jim Yingst]

Aside from looking at the file extension, a zip file (or jar file) should begin with a standard "magic number" in the first four bytes. You can check for it thus:

        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");

After that, to see if the whole thing is really a valid zip file, the easiest way is probably to open it up using the ZipFile class, read all the entries, and see if it throws an exception.