How to copy files in JAVA by bufferedInputStream and bufferedOutputStream?

Question

I would like to use bufferedInputStream and bufferedOutputStream to copy large binary files from source file to destination file.

Here is my code:

   byte[] buffer = new byte[1000];        
    try {
        FileInputStream fis = new FileInputStream(args[0]);
        BufferedInputStream bis = new BufferedInputStream(fis);

        FileOutputStream fos = new FileOutputStream(args[1]);
        BufferedOutputStream bos = new BufferedOutputStream(fos);

        int numBytes;
        while ((numBytes = bis.read(buffer))!= -1)
        {
            bos.write(buffer);
        }
        //bos.flush();
        //bos.write("\u001a");

        System.out.println(args[0]+ " is successfully copied to "+args[1]);

        bis.close();
        bos.close();
    } catch (IOException e)
    {
        e.printStackTrace();
    }

I can successfully copy but then I use

cmp src dest

in the command line to compare two files. The error message

cmp: EOF on files

appears. May I know where I was wrong?

data is there in file from which you are reading?? or any exception is coming?? — Prashant, Jan 23 '15 at 10:27

Jon Skeet · Accepted Answer · 2015-01-23T10:36:46.450

9

This is the mistake:

bos.write(buffer);

You're writing out the whole buffer, even if you only read data into part of it. You should use:

bos.write(buffer, 0, numBytes);

I'd also suggest using try-with-resources if you're using Java 7 or later, or put the close calls in a finally block otherwise.

As Steffen notes, Files.copy is a simpler approach if that's available to you.

edited Jan 23 '15 at 10:36

answered Jan 23 '15 at 10:27

Jon Skeet

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Thanks a lot! I tried bos.write(buffer, 0, numBytes). It works! – Jan 23 '15 at 10:36
@BinbinTang: Whoops, yes - fixed in the answer :) – Jon Skeet Jan 23 '15 at 10:36

score 2 · Answer 2 · answered Jan 23 '15 at 10:23

2

If you are using Java 8 try the Files.copy(Path source, Path target) method.

answered Jan 23 '15 at 10:23

Steffen

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some additional information about copying files: http://www.journaldev.com/861/4-ways-to-copy-file-in-java – Steffen Jan 23 '15 at 10:25

shikjohari · Answer 3 · 2015-01-23T10:34:29.953

2

you need to close your FileOutputStream and FileInputStream

Also you can use FileChannel to copy like as follows

FileChannel from = new FileInputStream(sourceFile).getChannel();
FileChanngel to = new FileOutputStream(destFile).getChannel();
to.transferFrom(from, 0, from.size());
from.close();
to.close();

edited Jan 23 '15 at 10:34

answered Jan 23 '15 at 10:27

shikjohari

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8
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That's copying a byte at a time though - very inefficient. – Jon Skeet Jan 23 '15 at 10:29
Yep, copy one byte per time is too inefficient. – Jan 23 '15 at 10:32
@JonSkeet yep modified, – shikjohari Jan 23 '15 at 10:38
I found that this didn't work when copying files larger (100GB) than the remaining free space on my C: drive (where the app is running). I am currently trying to use `BufferedInputStream` and `BufferedOutputStream` which appears to be working, but kinda slow. Is there an even faster version of this answer that doesn't require space free on the C: drive? Perhaps some version of the buffered streams? – trademark Nov 05 '20 at 18:25

Akvel · Answer 4 · 2015-01-23T10:48:36.380

0

You could use IOUtils from apatch-commons library

I think copyLarge fucntion it that you need

edited Jan 23 '15 at 10:48

answered Jan 23 '15 at 10:33

Akvel

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as stated in this article (http://www.journaldev.com/861/4-ways-to-copy-file-in-java), the apache-commons is the slowest solution. – Steffen Jan 23 '15 at 10:36

How to copy files in JAVA by bufferedInputStream and bufferedOutputStream?

4 Answers4