Re: java.io.File to java.lang.String

From:
Lew <lew@nospam.lewscanon.com>
Newsgroups:
comp.lang.java.programmer
Date:
Thu, 24 May 2007 23:57:54 -0400
Message-ID:
<u8udnZYqlOhfw8vbnZ2dnUVZ_umlnZ2d@comcast.com>
Tom Hawtin wrote:

      FileReader fileReader = new FileReader(file);
      CharBuffer charBuffer = CharBuffer.allocate((int)file.length());

This could allocate a buffer three times to large,


Jeff Higgins wrote:

Going over Javadocs... could you elaborate?


Because Strings and Chars are encoded, as are files. UTF-8, for example, uses
one to three bytes per character depending on the character set and other
factors.

I'm not sure about how Tom arrived at three times as large but I can easily
see how the CharBuffer could be twice as large as the file data. CharBuffers
are allocated at two bytes per character. A file encoding that uses 8 bits
per character will only fill half such a buffer. I'm guessing that Tom is
familiar with some combination of encoding schemes that would have the
CharBuffer wind up three times too large for the file.

or way too small for a huge file.


If the file uses a multibyte encoding with lots of characters that require
more than two bytes each.

      fileReader.read(charBuffer);

This does not necessarily read all that could be read. Should be in a
loop.


Again, I'm sorry but I haven't been able to figure out what might
cause read(charBuffer) to not read all that could be read?

Is this a sufficent loop?
while(fileReader.ready()){fileReader.read(charBuffer);}


No. You'll have to fill the buffer, flip() it, read it to store or processe
the data, then rewind() and repeat. I haven't played with java.nio much but
if I erred here someone should step up and correct me pretty quickly.

<http://java.sun.com/developer/technicalArticles/releases/nio/index.html>
<http://www.javaworld.com/javaworld/jw-09-2001/jw-0907-merlin.html>

GIYF.

--
Lew

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