Java Mystery: Directory Exists but Does Not?

Well, yesterday for me was another one of those days where you think your computer must be fooling you... There is an issue with a DirectoryCleaner that works for a subproject but does not when called from the parent. But first things first.

The openArchitectureWare Part

We are using oAW (yep, the new version which is part of Eclipse Modeling Project of Eclipse Galileo). Before generating the artifacts from the model, we are executing a directory cleaner that just rubs out the folders, for instance src/generated/java. The workflow file generate.mwe looks like this:

<workflow>
   <property file="generateAll.properties"/>
   <component class='org.eclipse.emf.mwe.utils.DirectoryCleaner' directory='${srcGenDir}'/>
   <component file='.../generateAll.mwe' inheritAll="true">
      <modelFile value='...' />
   </component>
</workflow>

srcGenDir is a property that is defined in the included properties file, but that's irrelevant. The highlighted line configures the mentioned directory cleaner. The relevant code snippet is invokeInternal() method of org.eclipse.emf.mwe.utils.DirectoryCleaner which is part of Eclipse EMF frameworks:

protected void invokeInternal(final WorkflowContext model, 
                 final ProgressMonitor monitor, final Issues issues) {
   if (directory != null) {
      final StringTokenizer st = new StringTokenizer(directory, ",");
      while (st.hasMoreElements()) {
         final String dir = st.nextToken().trim();
         final File f = new File(dir);
         if (f.exists() && f.isDirectory()) {
            ... do the cleanup ...
         }
      }
   }
}

Pretty simple, right? The directory attribute contains one or more directories (comma separated), hence a tokenizer is used to get each of them and to create a file. If this file exists and it's a directory, that will be erased.

The Maven Part

Of course we are using Maven to build the stuff. The Fornax Maven plugin is configured to call the workflow during Maven build. Moreover, the mentioned workflow is part of a subproject B which belongs to an outer multi-module project A.

Now, this is where the mystery begins... When I build B (the submodule), everything is fine and works like expected. However, when I build A (the parent project), B will be built in turn and its workflow is executed, but the directory is not cleaned up! You wouldn't expect this, right?

The Strange Part

In an attempt to find out what's going on, we put some debugging code into DirectoryCleaner. It turns out that the file f returns the same value for getAbsolutePath() in both cases, but f.exists() reveals false when the build is started from the parent project – hence the condition is not met and nothing will be cleaned up.

Unfortunately, you can't look any deeper into the native code that is called when determining if a file exists. So, in a kind of trial and error approach, we found out that using the following code fixes the issue:

protected void invokeInternal(final WorkflowContext model, 
                 final ProgressMonitor monitor, final Issues issues) {
   if (directory != null) {
      final StringTokenizer st = new StringTokenizer(directory, ",");
      while (st.hasMoreElements()) {
         final String dir = st.nextToken().trim();
         final File f1 = new File(dir);
         final File f = new File(f1.getAbsolutePath());
         if (f.exists() && f.isDirectory()) {
            ... do the cleanup ...
         }
      }
   }
}

That is: by creating another file that is using the absolute path of the first one and using this further on, everything is fine in both scenarios – whether called from parent project or submodule.

To be honest: I have no explanation for these findings. Why is File behaving differently? When calculating the exist flag, the code should take into account the file's absolute path, right? So, why is creation of another file based on the absolute path is fixing the issue? Any insights are deeply appreciated...!