PRB: "Thumbnails are not generated"

Overview

Some of the customers contacted our support and reported the strange problem with thumbnail generation in Image Uploader Java. It means that Image Uploader neither does not show thumbnails in folder pane nor does not upload thumbnails to a server. It displays and uploads icons instead.
The symptoms are the following:

1. If selected image is smaller than specified thumbnail size, thumbnail is displayed in folder pane and can be uploaded to a server without a problem,
2. If selected image is larger than thumbnail size, thumbnail is not generated.

Reason

Image Uploader uses several algorithms to generate thumbnails. It switches between them dynamically using reflection. It means that the applet tries to load some particular modules from a server. If it does not find them, it uses standard built-in algorithm.

Imagine that your server is set up to return status code 200 (success) for non-existent URLs (for example, you server returns HTML page saying that this resource is not available… and so on). In this case when Image Uploader requests the module, server answers “success”. Actually the applet does not get the module but it “does not know” about it and “thinks” that the module is downloaded and ready to use. The applet tries to use it during thumbnail generation operations and fails. So that is why thumbnails are not generated.

Resolution

The settings of server should be modified to return status code 404 for non-existent *.java files requested from the server.