CODEWITHSUNDEEP
javastringfile-iofilewriter
Chad Mourning
Chad Mourning

Reputation: 619

FileWriter writing extra nulls at end of file

For large strings (60MB or so long), FileWriter is appending extra nulls to the end of my files. For small strings this code works as expected.

For clarity, dat and filePath are Strings.

FileWriter fstream = new FileWriter( filePath );
fstream.write( dat );
fstream.close();

File f = new File( filePath );         
System.out.println("Data: " + dat.length() + ", File: " + f.length());

In short, under what circumstances, should the two printed values be different?

Here's my example output:

Data: 63833144, File: 63833728

I got 584 extra nulls at the end of file for some reason. I find it reasonable that the string might be over allocated, but these shouldn't print to file, right ? To make things worse, if I explicitly give it the length:

fstream.write(dat, 0, dat.length());

The behavior is the same. Coincidentally, if I say (dat.length() - 584), it does what I want, but only in this specific case.

Any ideas?

JDK version: 1.7.0_02

Edited: Add file types for variables (both Strings)

Upvotes: 3

Views: 3781

Answers (4)

Evgeniy Dorofeev
Evgeniy Dorofeev

Reputation: 136042

The file length depends on encoding. This test

System.out.println(dat.getBytes().length);

will show the length in bytes after encoding, because String.getBytes will use the same encoding (default) as new FileWriter(file)

Upvotes: 1

maxammann
maxammann

Reputation: 1048

So run a test with a 63833144 long string with only 'A's in it and the output is: Data: 63833144, File: 63833144

So Im sure the problem is a encoding problem.

(I would have post this as comment but because I have not 50 rep Im not able to :/)

Upvotes: 0

mightyrick
mightyrick

Reputation: 910

What is "dat"? If "dat" is a StringBuffer, you need to be careful. If the length of the StringBuffer is greater than its contents, then nulls will be appended to the end. You might try to use dat.toString(). The null characters will be trimmed in the conversion, I believe.

Upvotes: 2

Alexander Pogrebnyak
Alexander Pogrebnyak

Reputation: 45576

I suggest that you never use FileWriter, because it is using default encoding on your platform to convert String to byte stream.

Instead you should do this:

Writer writer =
  new OutputStreamWriter( 
    new FileOutputStream( fileName ),
    // Always specify encoding compatible with your string
    "UTF-8"
  );

try
{
  writer.write( dat );
  writer.flush( );
}
finally
{
  writer.close( );
}

Also, the String length and resulting byte stream length don't have to match. They will match only for ASCII text string.

Upvotes: 1

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