Get the number of bytes of a file behind a Java InputStream

Question

As the title says, I need to know how many bytes the file has that's "behind" an InputStream. I don't want to download all bytes and count (takes to long). I just need to know how many bytes the file has.

Like this:

int numberOfBytes = countBytes(inputStream);

So, I need an implementation for countBytes(InputStream inputStream)

Take a look at this post: http://stackoverflow.com/questions/116574/java-get-file-size-efficiently — Mike Yockey, Dec 14 '11 at 14:00
Do you have access to the file, or just an InputStream to it? — Todd, Dec 14 '11 at 14:00
@Todd I only got the stream which refers to an attachment of an email on an imap server via Javamail API. — Timo Ernst, Dec 14 '11 at 14:09
@yock That won't help. The link you posted refers to getting the size from an instanceof File. I only got the stream. — Timo Ernst, Dec 14 '11 at 14:10

NPE · Accepted Answer · 2011-12-14T14:06:48.060

8

Other than by consuming the entire stream and counting the bytes, you can't (there's no API for it).

There's the available() method, but it quite explicitly doesn't do what you're asking:

Note that while some implementations of InputStream will return the total number of bytes in the stream, many will not.

If the InputStream is associated with a file (and not, say, a socket), perhaps you could use a different API to get its size?

edited Dec 14 '11 at 14:06

answered Dec 14 '11 at 13:59

NPE

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Nah, I think it's a socket. The input stream refers an attachment of an email via Javamail. – Timo Ernst Dec 14 '11 at 14:08
Hi @Timo have you found any other solution for this ? – StrawhatLuffy Sep 08 '16 at 12:01
@StrawhatLuffy Sorry, it's so long ago, I don't remember :-) – Timo Ernst Sep 10 '16 at 20:26

score 2 · Answer 2 · answered Dec 14 '11 at 15:29

2

Could you leverage skip() in some way to approximate the size of the file?

int bytes = 1024; // Chunk size for skipping. Adjust as necessary
try {
    int skipped = 0;
    while(stream.available()) {
        stream.skip(bytes);
        skipped += bytes;
        // Elided...do something with skipped
    }
} catch(IOException ex) {
    // Handle a skip that's too big
}

I'm sure too that you could make this loop smarter and avoid the inevitable IOException, but that's an exercise left to the reader.

answered Dec 14 '11 at 15:29

Mike Yockey

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As I said before, I need the EXACT byte size – Timo Ernst Dec 14 '11 at 16:26
Then can you skip one byte at a time? Why do you need to know the exact size? – Mike Yockey Dec 14 '11 at 17:21
I am uploading a file to Dropbox and its API needs the exact amount of bytes that I am uploading. – Timo Ernst Dec 15 '11 at 15:00

Get the number of bytes of a file behind a Java InputStream

2 Answers2

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