Eclipse JDT: How to get java package name of a non-existing IFolder - eclipse-rcp

Question

Given an IFolder instsance fd (fd may or may not exist), how to get the java package name if fd represents a java package? Currently I coded in this way
IJavaProject jp = JavaCore.create(fd.getProject());
IPackageFragment pf = jp.findPackageFragment(f.getFullPath());
String pname = pf.getElementName();
The code failed when fd does not exist (for example it was just deleted and the deletion was caught in IResourceDelta of an IResourceChangeListener), as IJavaProject#findPackageFragment(IPath) returns null for non-existing item. How to get the package name for a non-existing IFolder? Thanks

Answer 1

Does the inexistent IFolder still have a useful parent chain? If so, you may want to find the parent that corresponds to a package fragment root of the current project.
IContainer parent = fd.getParent();
while (parent != null) {
if (JavaCore.create(parent) instanceof IPackageFragmentRoot)
// success: parent is a source folder
else
parent = parent.getParent();
}
Then take the relative path from the package fragment root to the folder as the package name.
IPath myPath = fd.getFullPath();
IPath parentPath = parent.getFullPath();
IPath packagePath = myPath.makeRelativeTo(parentPath);
PS: per JLS a package is only observable if a compilation unit in the package is observable. Ergo an inexistent folder can never represent a package (but I admit this is picking on words).