Question

I am trying to copy a file using the following code:

1:

        int data=0;
        byte[] buffer = new byte[4096];
        while((data = bufferedInputStream.read())!=-1){
            bufferedOutputStream.write(data);
        }

2:

        byte[] buffer = new byte[4096];
        while(bufferedInputStream.read(buffer)!=-1){
            bufferedOutputStream.write(buffer);
        }

Actual size of file is 3892028 bytes(on windows). The file will be uploaded by the user thro struts2 fileupload. Uploaded file size is exactly same as that of windows. When I try to copy the uploaded file from temporary folder, the copied file varies in size and the time taken also varies(it is negligible). Please find the below readings.

Without using buffer(Code 1)
Time taken 77
3892028
3891200

Buffer size 1024(Code 2)
Time taken 17
3892028
3891200

Buffer size 4096(Code 2)
Time taken 18
3892028
3891200

Buffer size 10240(Code 2)
Time taken 14
3892028
3901440

Buffer size 102400(Code 2)
Time taken 9
3892028
3993600

If I increase the buffer size further, time taken increases, again it is negligible. So my questions are,

1. Why the file size changes?
2. Is there any subtle consequences due to this size variation?
3. What is the best way to accomplish this functionality(copying a file)?

I don’t know what is going beneath? Thanks for any suggestion.
Edit: I have flush() and close() method calls.
Note: I have trimmed my code to make it simpler.

Answer 1

1. Why the file size changes?

You forgot to `flush()` (and `close()`):

bufferedOutputStream.flush()

Also you should pass the number of bytes read to write method:

bufferedOutputStream.write(data, 0, bytesRead);

1. What is the best way to accomplish this functionality(copying a file)?

• FileUtils.copyFile()
• IOUtils.copy()

Both from apache-commons IO.