What URL.setFileNameMap(FileNameMap map) is used for?

Question

What URL.setFileNameMap(FileNameMap map) method does, how to use it correctly and what is it used for? Is it any useful at all?

Docs are not very much of an explanation:

public static void setFileNameMap(FileNameMap map)

Sets the FileNameMap

+

public static FileNameMap getFileNameMap()

Loads filename map (a mimetable) from a data file. It will first try to load the user-specific table, defined by "content.types.user.table" property. If that fails, it tries to load the default built-in table.

What is a mimetable and FileMap?

P.S. I read the docs for interface FileNameMap. It is also very brief and gives me no clue:

A simple interface which provides a mechanism to map between a file name and a MIME type string.

String getContentTypeFor(String fileName)

Gets the MIME type for the specified file name. Returns: a String indicating the MIME type for the specified file name.

P.S. There is a question about FileNameMap here, but it was not accepted and does not answer my question.

Answer 1

This FileNameMap is internally used by method URLConnection.guessContentTypeFromName(String).
It is implemented like this:

public static String guessContentTypeFromName(String fname) {
    return getFileNameMap().getContentTypeFor(fname);
}