Java Network Programming, Second Edition

MIME

MIME is an open standard for sending multipart, multimedia data through Internet email.^[9] The data may be binary, or it may use multiple ASCII and non-ASCII character sets. Although MIME was originally intended for email, it has become a widely used technique to describe a file’s contents so that client software can tell the difference between different kinds of data. For example, a web browser uses MIME to tell whether a file is a GIF image or a printable PostScript file.

MIME supports almost a hundred predefined types of content. Content types are classified at two levels: a type and a subtype. The type shows very generally what kind of data is contained: is it a picture, is it text, is it a movie? The subtype identifies the specific type of data: GIF image, JPEG image, TIFF image. For example, HTML’s content type is text/html; the type is text, and the subtype is html. The content type for a GIF image is image/gif; the type is image, and the subtype is gif. Table 3.2 lists the more common defined content types. On most systems, a simple text file maintains a mapping between MIME types and the application used to process that type of data; on Unix, this file is called mime.types. The most current list of registered MIME types is available from ftp://ftp.isi.edu/in-notes/iana/assignments/media-types/media-types.^[10]

The data returned by an HTTP 1.0 or 1.1 web server is sent in MIME format. Most web servers and clients understand at least two MIME text content types, text/html ...