MIME types file search order:

The MimetypesFileTypeMap looks in various places in the user's system for MIME types file entries. When requests are made to search for MIME types in the MimetypesFileTypeMap, it searches MIME types files in the following order:

1. Programmatically added entries to the MimetypesFileTypeMap instance.
2. The file .mime.types in the user's home directory.
3. The file mime.types in the Java runtime.
4. The file or resources named META-INF/mime.types.
5. The file or resource named META-INF/mimetypes.default (usually found only in the activation.jar file).

(The current implementation looks for the mime.types file in the Java runtime in the directory java.home/conf if it exists, and otherwise in the directory java.home/lib, where java.home is the value of the "java.home" System property. Note that the "conf" directory was introduced in JDK 9.)

MIME types file format:

# comments begin with a '#'
# the format is <mime type> <space separated file extensions>
# for example:
text/plain txt text TXT
# this would map file.txt, file.text, and file.TXT to
# the mime type "text/plain"