Java I/O catch file exist

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morc - 07 Feb 2006 17:05 GMT

hi,
how do you check if a file exist before you write to it?

I have a registration page which creates a txt file named the username
the user chooses
once registration is complete

Now i don't want user to be overwritten so how do i check if the file
already exists first before writing?

thanks
-morc

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morc - 07 Feb 2006 17:07 GMT

i forgot to mention i am using FileWriter

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Joe Attardi - 07 Feb 2006 17:22 GMT

> hi,
> how do you check if a file exist before you write to it?

Before creating your FileWriter, you can create a new File object
around the file you want to check, then call the exists() method on it.

File txtFile = new File("myfile.txt");
if (txtFile.exists()) { ... } // the file already exists
else { ... } // the file does not exist

Hope this helps..

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Joe Attardi

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Gordon Beaton - 07 Feb 2006 17:28 GMT

> File txtFile = new File("myfile.txt");
> if (txtFile.exists()) { ... } // the file already exists
> else { ... } // the file does not exist

In the interest of avoiding a race condition, this is a better
mechanism since File.create() tests and creates the file atomically,
and only if the file doesn't already exist:

File txtFile = new File("myfile.txt");

if (txtFile.createNewFile()) {
// a new file was created
}
else {
// the file already existed
}

/gordon

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Joe Attardi - 07 Feb 2006 17:31 GMT

> In the interest of avoiding a race condition, this is a better
> mechanism since File.create() tests and creates the file atomically,
> and only if the file doesn't already exist:

Good call, Gordon. Shame on me for missing this one...

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morc - 07 Feb 2006 17:43 GMT

yes perfect thanks again

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Thomas Fritsch - 07 Feb 2006 17:26 GMT

> how do you check if a file exist before you write to it?

String fileName = ...;
File file = new File(fileName);
if (file.exists())
...do something
else
...do something else

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Roedy Green - 08 Feb 2006 23:17 GMT