RFR [8020669] java.nio.file.Files.readAllBytes() does not read any data when Files.size() is 0

Ivan Gerasimov ivan.gerasimov at oracle.com
Sat Jul 20 22:15:27 UTC 2013

Roger, David thanks for suggestions!

Would you please take a look at an updated webrev?

- File size is used as an initial size of BAOS's buffer.
- BAOS avoids copying its buffer in toByteArray(), if size is correct .

I don't want to initialize BAOS with a positive number if size happened 
to be zero.
Because zero could indicate that the file is really empty.

Sincerely yours,

On 19.07.2013 22:30, David M. Lloyd wrote:
> My mistake, we're not talking about strings.  Still you can subclass 
> and determine whether the buffer size guess was right, and if so 
> return the array as-is (swap in an empty array or something as needed).
> On 07/19/2013 01:28 PM, David M. Lloyd wrote:
>> It's trivial to subclass ByteArrayOutputStream and add a method which
>> converts its contents to a string using the two protected fields which
>> give you all the info you need to do so.  So no extra copy is needed
>> that you aren't already doing.
>> On 07/19/2013 01:06 PM, roger riggs wrote:
>>> Hi Ivan,
>>> I think this change takes too big a hit for the cases where the size is
>>> correct.
>>> No real file system can be wrong about the size of a file so this is a
>>> problem
>>> only for special file systems. If the problem is with size reporting 
>>> zero
>>> then maybe using the incremental read only for size == would be a 
>>> better
>>> fix.
>>> At least you could pass the size to the constructor for BAOS and avoid
>>> the thrashing for every re-size; but still it will allocate and create
>>> an extra copy
>>> of the every time.
>>> $.02, Roger
>>> On 7/19/2013 1:15 PM, Ivan Gerasimov wrote:
>>>> Hello everybody!
>>>> Would you please review a fix for the problem with
>>>> j.n.f.Files.readAllBytes() function?
>>>> The current implementation relies on FileChannel.size() to preallocate
>>>> a buffer for the whole file's content.
>>>> However, some special filesystems can report a wrong size.
>>>> An example is procfs under Linux, which reports many files under /proc
>>>> to be zero sized.
>>>> Thus it is proposed not to rely on the size() and instead continuously
>>>> read until EOF.
>>>> The downside is reallocation and copying file content between buffers.
>>>> But taking into account that the doc says: "It is not intended for
>>>> reading in large files." it should not be a big problem.
>>>> http://bugs.sun.com/view_bug.do?bug_id=8020669
>>>> http://cr.openjdk.java.net/~igerasim/8020669/0/webrev/
>>>> The fix is for JDK8. If it is approved, it can be applied to JDK7 as
>>>> well.
>>>> Sincerely yours,
>>>> Ivan Gerasimov

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