Taking the Contents of a File object and converting it to a byte array

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MattC - 30 Dec 2005 16:33 GMT

I have a file that I need to read into my program and convert to a byte
array (byte [] ). The code below works but it seems sort of "smelly".
Can someone suggest a cleaner, more eloquent, way of accomplishing
this?

Thanks!

****************

/* Move the data in the File object to a byte array */
InputStream in = new FileInputStream(templateFile);
int length = new Long(templateFile.length()).intValue();
ByteArrayOutputStream out = new ByteArrayOutputStream(length);

byte[] buf = new byte[1024];
int len;

while ((len = in.read(buf)) > 0) {
out.write(buf, 0, len);
}

byte[] certBytes = new byte[out.size()];
certBytes = out.toByteArray();

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Thomas Hawtin - 30 Dec 2005 17:16 GMT

> I have a file that I need to read into my program and convert to a byte
> array (byte [] ). The code below works but it seems sort of "smelly".
> Can someone suggest a cleaner, more eloquent, way of accomplishing
> this?

What smells about it to you?

> /* Move the data in the File object to a byte array */

You should ensure that you always close the stream.

> InputStream in = new FileInputStream(templateFile);

try {

> int length = new Long(templateFile.length()).intValue();
> ByteArrayOutputStream out = new ByteArrayOutputStream(length);
>
> byte[] buf = new byte[1024];

A bit small in this day an age, I think. I go for 8192 out of habit.
Unlikely to make much difference.

> int len;
>
> while ((len = in.read(buf)) > 0) {

I prefer to avoid side effects in conditional expressions, and also
testing explicitly against -1. A value of 0 probably should not break
the loop.

> out.write(buf, 0, len);
> }

} finally {
in.close();
}

The allocation is entirely pointless as the next line overwrites the array.

> byte[] certBytes = new byte[out.size()];
> certBytes = out.toByteArray();

You could read the length of the file first and allocate an exact sized
buffer, but the code above is safer and less tied to specifics.

Tom Hawtin

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Unemployed English Java programmer
http://jroller.com/page/tackline/

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Roedy Green - 30 Dec 2005 18:02 GMT

> int length = new Long(templateFile.length()).intValue();

this is a bit roundabout. Try
int length = (int) templateFile.length();

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Canadian Mind Products, Roedy Green.
http://mindprod.com Java custom programming, consulting and coaching.

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Roedy Green - 30 Dec 2005 18:05 GMT

> /* Move the data in the File object to a byte array */
> InputStream in = new FileInputStream(templateFile);
[quoted text clipped - 10 lines]
> byte[] certBytes = new byte[out.size()];
> certBytes = out.toByteArray();

You can read the entire file of raw bytes in one i/o into your
certBytes. See http://mindprod.com/applets/fileio.html

You don't need a ByteArrayOutputStream or a byte[1024] buffer.

Even if you did need a buffer, use a BufferedInputStream rather than
rolling your own.

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Canadian Mind Products, Roedy Green.
http://mindprod.com Java custom programming, consulting and coaching.

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Thomas Hawtin - 30 Dec 2005 20:12 GMT

>> /* Move the data in the File object to a byte array */
>> InputStream in = new FileInputStream(templateFile);
>> int length = new Long(templateFile.length()).intValue();

(I didn't see that...)

> You don't need a ByteArrayOutputStream or a byte[1024] buffer.
>
> Even if you did need a buffer, use a BufferedInputStream rather than
> rolling your own.

You don't mean reading a byte at a time, do you? If nothing else, the
synchronisation would kill performance, unless the JVM was something
special.

Tom Hawtin

Signature

Unemployed English Java programmer
http://jroller.com/page/tackline/

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Taking the Contents of a File object and converting it to a byte array

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