Most efficient way to create a large file (> 1GB)

Question

I would like to know what is the most efficient way to create a very large dummy File in java. The filesize should be just above 1GB. It will be used to unit test a method which only accepts files <= 1GB.

possible duplicate of [Create file with given size in Java](http://stackoverflow.com/questions/245251/create-file-with-given-size-in-java) — meriton, Sep 27 '10 at 12:49

score 14 · Accepted Answer · edited May 23 '17 at 12:33

14

Create a sparse file. That is, open a file, seek to a position above 1GB and write some bytes.

Relevant: Create file with given size in Java

edited May 23 '17 at 12:33

Community

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answered Sep 27 '10 at 12:38

Sjoerd

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score 2 · Answer 2 · answered Sep 27 '10 at 12:36

2

Can't you make a mock which returns filesize of > 1GB? File IO doesn't sound very unit-testy to me (although that depends on what your idea of a unit test is).

answered Sep 27 '10 at 12:36

Skilldrick

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I want to test a piece of code which loads a file from disk based on a filename and does some validation checks. So it has to be a real file. – Fortega Sep 27 '10 at 12:47

score 1 · Answer 3 · answered Jul 15 '15 at 15:24

Made this function to create sparse files

private boolean createSparseFile(String filePath, Long fileSize) {
    boolean success = true;
    String command = "dd if=/dev/zero of=%s bs=1 count=1 seek=%s";
    String formmatedCommand = String.format(command, filePath, fileSize);
    String s;
    Process p;
    try {
        p = Runtime.getRuntime().exec(formmatedCommand);

        p.waitFor();
        p.destroy();
    } catch (IOException | InterruptedException e) {
        fail(e.getLocalizedMessage());
    }
    return success;
}

Most efficient way to create a large file (> 1GB)

3 Answers3