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From: Eric Sosman <esosman@ieee-dot-org.invalid>
Newsgroups: comp.lang.java.programmer
Subject: Re: How to append "test" to a filename (after path and before extension)?
Date: Thu, 25 Aug 2011 07:30:02 -0400
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On 8/25/2011 5:50 AM, Jochen Brenzlinger wrote:
> Let's start with a filename which is stored in a String variable e.g.
>
> String fn = "D:\project\java\testproj\log2011.log"

     Aside: Those backslash characters need some attention ...

> I want to append "test" to the file basename but keep path and extension.
> The resulting filename for the example above should be:
>
> string fn2 = "D:\project\java\testproj\log2011test.log"
>
> How can I do this programmatically from Java?

     A bare-bones approach:

	int dot = fn.lastIndexOf('.');
	String fn2 = fn.substring(0, dot) + "test" + fn.substring(dot);

In actual use you'd want some sanity checking to be sure the '.'
is in fact present and is after the last '\', so you wouldn't
get fooled by

	D:\project\java\testproj\config
or
	D:\project\java\testproj.old\data

You could guard against such things by using fn.lastIndexOf('\\')
to locate the rightmost back-slash and checking that the '.' does
in fact appear even further right.  However, I think you're better
off using the File class to chop up and reassemble file names in a
(mostly) platform-independent way, e.g.

	File base = new File(fn);
	String name = base.getName();  // handles / or \ or whatever
	int dot = name.lastIndexOf('.');
	String newname = (dot < 0) ? name + "test"
	    : name.substring(0, dot) + "test" + name.substring(dot);
	File test = new File(base.getParentFile(), newname);
	String fn2 = test.getPath();  // if needed

This may seem like a lot of running around for little effect, but
it protects you from some unpleasant surprises in the long run.

-- 
Eric Sosman
esosman@ieee-dot-org.invalid