I need to upload files and folders to the server while preserving the hierarchy. At the moment I am using a plugin multiFileUpload that allows you to upload multiple files at the same time, but it ignores the selected folders. I know that neither vaadin nor Html5 has a universal solution that works everywhere for uploading folders.
I'm ready to write my own solution, but climbed the Internet can't find a way to display file selection (perhaps there will a JavaScript call) but the main question - is it possible somehow to POST a request Vaadin's and upload files by way of creating subfolders in which they were?
You can only upload files, not folders. It's simply not doable.
You can upload any number of files, but they won't be structured into folders.
I see two possibilities how you could still achieve what you need if you really wanted to, even if it changes the user experience a bit:
Let the user upload a .zip file of his folder structure. When they upload it, you unzip it on the server side and have now access to all the files in the correct folder structure.
Let the user upload all his files within his folder structure. After all files have been uploaded, You display all the files in a TreeGrid where the user can recreate the original structure using Drag-and-Drop or similar.