Write byte[] to file

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andrewzzz - 20 Nov 2006 13:04 GMT

hi guys,
what is the best way to write a byte array to a file?
thanks a lot,bye

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Paul Davis - 20 Nov 2006 13:45 GMT

public void writeFile(byte[] data, String fileName) throws IOException{
    OutputStream out = new FileOutputStream(fileName);
    out.write(data);
    out.close();
}

> hi guys,
> what is the best way to write a byte array to a file?
> thanks a lot,bye

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Thomas Hawtin - 20 Nov 2006 13:52 GMT

> public void writeFile(byte[] data, String fileName) throws IOException{
> OutputStream out = new FileOutputStream(fileName);

try {

> out.write(data);

} finally {

> out.close();

}

> }
>> hi guys,
>> what is the best way to write a byte array to a file?
>> thanks a lot,bye

Tom Hawtin

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M.J. Dance - 20 Nov 2006 13:50 GMT

> hi guys,
> what is the best way to write a byte array to a file?

This question screams for a how-to-make-a-rat-pie recipe type of an answer. So,
without further ado...

1. First you have to obtain those bytes. The best way is to read them from a file:

File file = new File("afile");
InputStream in = new FileInputStream(file);
byte[] bytes = new byte[file.length()];
in.read(bytes);
in.close();

//Exception handling is left to a gentle reader.

2. Now write them to a file.

Simple, heh?

For other not-so-best ways you can also resort to

http://java.sun.com/docs/books/tutorial/essential/io/

or, if the going gets extremely tough,

http://www.justfuckinggoogleit.com/search?q=java+file+io+tutorial

Ta ta!

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Thomas Hawtin - 20 Nov 2006 14:31 GMT

> InputStream in = new FileInputStream(file);
> byte[] bytes = new byte[file.length()];
> in.read(bytes);
> in.close();

Are you sure you don't want to check the return value of read, or use
another method from a decorator?

> or, if the going gets extremely tough,
>
> http://www.justfuckinggoogleit.com/search?q=java+file+io+tutorial

There's a lot of really bad advice on the web. Er, and on Usenet. Oh and
in books too.

Tom Hawtin

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Chris Uppal - 20 Nov 2006 17:45 GMT

> byte[] bytes = new byte[file.length()];
> in.read(bytes);

/NEVER/ do that. Never !

(There are other problems with the code too, but that one is unforgivable, even
for throwaway code).

-- chris

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Thomas Fritsch - 20 Nov 2006 18:30 GMT

>>byte[] bytes = new byte[file.length()];
>>in.read(bytes);
>
> /NEVER/ do that. Never !

It should be replaced by something like this:

byte[] bytes = new byte[file.length()];
for (int n = 0, x; n < bytes.length; n += x ) {
x = in.read(bytes, n, bytes.length - n);
if (x < 0)
throw new EOFException("stream shorter than expected");
}

Signature

Thomas

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Mark Rafn - 20 Nov 2006 19:43 GMT

>>>byte[] bytes = new byte[file.length()];
>>>in.read(bytes);

>> /NEVER/ do that. Never !

>It should be replaced by something like this:
>
[quoted text clipped - 4 lines]
> throw new EOFException("stream shorter than expected");
> }

As long as you're checking for files that got shorter between creating your
byte array and actually reading, you might want to check that it got longer
with in.available() or just by reading another byte and seeing if one's there.

Alternately, you may prefer to just read whatever you can and not trust the
file.length() call at all. This works even if you're not reading from a file
(like from getResourceAsStream() or a network stream).

// best-guess starting size, make it up if we don't have a file.
ByteArrayOutputStream baos = new ByteArrayOutputStream(file.length());
byte[] buf = new byte[1024]; // read up to 1k at a time
boolean done=false;
while (!done) {
int amtRead = in.read(buf);
if (amtRead == -1) {
done = true; // EOF
} else {
baos.write(buf, 0, amtRead);
}
}
byte[] bytes = baos.toByteArray();
--
Mark Rafn dagon@dagon.net <http://www.dagon.net/>

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Write byte[] to file

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