Java library function to find shadow file in different directory

Question

I often have code where I loop over a directory (including subdirectories) and need to move / copy the file to a different directory. What I find tedious is the process of identifying where the file will go. I have often done that, usually like this:

File shadow = new File(sourceFile.getAbsolutePath()
                        .replace(
                             sourceFolder.getAbsolutePath(),
                             targetFolder.getAbsolutePath()
                        )
              );

My question: is there a standard routine to do this or something similar in any major open source library? I didn't find one in Commons IO anyway...

I am not looking for complete move / copy solutions, I know tons of those. I just want the equivalent of the above code.

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An Example, as requested:

Source folder:

src/main/resources

Target folder:

target/classes

Source file:

src/main/resources/com/mycompany/SomeFile.txt

Target file (the one I'm looking for):

target/classes/com/mycompany/SomeFile.txt

(I usually do stuff like this in a maven context, hence these folders but they could be non-maven folders, as well, the question has nothing to do with maven)

Answer 1

Have you seen the org.apache.commons.io.FilenameUtils concat method? It takes a base directory (your target) and file-name to append. You would need to calculate the sourceFolder prefix ("src/main/resources".length()) and do a substring. Something like:

File shadow = new File(FilenameUtils.concat(targetFolder.getAbsolutePath(),
    sourceFile.getAbsolutePath().substring(prefixLength));

Not much better than rolling you own though.

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For posterity, Apache's org.apache.commons.io.FileUtils also has functionality that you might use although I don't see a specific solution to your question:

• FileUtils.moveFileToDirectory()
• FileUtils.copyDirectory()
• FileUtils.moveDirectory()

You could use copyDirectory with a FileFilter to choose which files to move over:

• FileUtils.copyDirectory(File, File, FileFilter)

Answer 2

What you are looking for I have never found either but it will exist soon when JDK 7 (eventually) crawls out the door.

Path.relativize(Path) (Java 7 API)

For now I would stick to your current solution (or roll your own equivalent of the above).