Upload a set of .png files and save into a HashMap

Question

I need to upload a Folder with sum x of .png files and save them into a hashmap. How can I achieve this. My thought was

    HashMap<Integer,Image> map = new HashMap<>();
    for (int i= map.size();map>0;map-- ){
        map.put(i, new Image(new FileInputStream("C:\\Users\\drg\\Documents\\image"+i+".png")));
    }

the problem is, in the beginning my HashMap contains 0 items, therefor it will always remain 0. So how can I add the .png files to my HashMap if I dont know how many .png files are in my folder.

Another problem is that I am using the FileInputStream and need to know the exact "name" of the .png file. How can I find out how many .png files there are and upload them into my HashMap without needing to know their exact filename?

Answer 1

All you need to do is list the contents of the folder and find the matching file names. E.g. using the java.nio API and putting the images into a list:

Path folder = FileSystems.getDefault().getPath("Users", "drg", "Documents");
List<Image> images = Files.list(folder)
    .filter(path -> path.getFileName().toString().matches("image\\d+\\.png"))
    .map(Path::toUri)
    .map(URI::toString)
    .map(Image::new)
    .collect(Collectors.toList());

Or using the old java.io API:

File folder = new File("C:/Users/drg/Documents");
File[] imageFiles = folder.listFiles(file -> file.getName().matches("image\\d+\\.png"));
List<Image> images = new ArrayList<>();
for (File file : imageFiles) {
    images.add(new Image(file.toURI().toString()));
}

If you need to index them by the integer, it's reasonably easy to extract that integer value when you have the filename.