Build CheckboxTree from the selected project files

Hey!

First of all I want to say that I'm not from the Java world =)

The task that I want to solve: select the selected files / folders in the dialog in CheckboxTree with the structure preserved and filtering "images only". I was faced with a problem in choosing the approach to solving the problem.

Here is the test structure:

Initially, I selected the top level of the folder and then it's enough to build a model for CheckboxTree using recursion. But there are problems there is a choice like this: 

Or even more complicated, like this

There are a lot of problems: for each received VirtualFile [] it is necessary to receive parents and descendants, and also duplication.

So I decided to rely on the file paths in VFS:

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VirtualFile[] files = e.getData(CommonDataKeys.VIRTUAL_FILE_ARRAY);

List<VirtualFile> imageFiles = new ArrayList<>();
List<VirtualFile> uniqueImageFiles = new ArrayList<>();

// Filtering
for (VirtualFile file : files) {
    VfsUtil.visitChildrenRecursively(file, new VirtualFileVisitor() {
    @Override
        public boolean visitFile(@NotNull VirtualFile file) {
            if (file.isInLocalFileSystem() && allowedExtensions.contains(file.getExtension())) {
                imageFiles.add(file);
            }

            return file.isInLocalFileSystem() && file.isDirectory();
        }

    });
}

// Clear duplicate
for (VirtualFile file : imageFiles) {
    if (!uniqueImageFiles.contains(file)) { 
        uniqueImageFiles.add(file);
    }
}
--------

So in uniqueImageFiles, I have everything I need (including children as image files). For each VirtualFile, I execute:

--------
for (VirtualFile file : uniqueImageFiles) {
    // Getting a relative path without the file itself
    String relativePath = file.getParent().getPath().replace(project.getBasePath(), "");
    relativePath = StringUtils.strip(relativePath, "/");

    // Explode path-string to segments
    String[] pathSegments = relativePath.split("\\/", -1);

    buildTreeBranch(pathSegments, file, parentNode);
}
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Thus, I build a model for CheckboxTree easily and simply, keeping the whole structure completely.

But I'm worried about some questions:
1. How many safe pieces of code (file always image):

---------
Project project = ProjectManager.getInstance().GetOpenProjects()[0];
String relativePath = file.getParent().GetPath ().Replace(project.getBasePath (), "");
---------

2. Is there a simple way to get a relative path for VirtualFile?

3. I'm not sure about the correct approach