Java FileInputStream 在 Windows 和 Linux 中表现出不同的行为

Question

I came across a strange issue when writing unit tests for cross-platform Java applications, specifically using the FileInputStream. This test was originally written in Windows and passed

        FileInputStream inputStream = new FileInputStream(file.getAbsolutePath());
        FileOutputStream outputStream = FileUtils.getFileOutputStream(file.getAbsolutePath());

        outputStream.write('a');
        outputStream.close();


        Assert.assertEquals(inputStream.read(), 'a');

This works perfectly in Windows but fails in Ubuntu as inputStream returns -1 (which is EOF)

However if I reassign inputStream after I close outputStream like so,

        FileInputStream inputStream = new FileInputStream(file.getAbsolutePath());
        FileOutputStream outputStream = FileUtils.getFileOutputStream(file.getAbsolutePath());

        outputStream.write('a');
        outputStream.close();

        inputStream = new FileInputStream(file.getAbsolutePath());

        Assert.assertEquals(inputStream.read(), 'a');

everything works fine in Ubuntu and Windows.

My guess is that it has to do with the different file systems used by Windows and Ubuntu but I was hoping someone could elaborate further.

note: The FileUtils class is custom but works correctly. I checked that the file was being written to in both OS's manually

Answer 1

On windows, while a file is opened it cannot be deleted, nor the directory it is in etc. The FileOutputStream can only truncate the file, it cannot delete and replace it. On Unix, the file lives independently of the directory structure. It can be open, read and written to even if it no longer appears in any directory. This means that FileOutputStream can delete the file and re-create it rather re-use the existing inode.

The difference is whether the file is truncated or replaced. On Linux a file can be replaced even if it is open, on Windows it cannot.