Exploring the J2EE Data Formats

Data formats define the types of data that can be exchanged between different components residing in different tiers. The J2EE architecture supports for the following data formats:

• HTML documents— The markup language used to define hypertext documents accessible over the Internet. HTML enables many display elements to be included in a Web page, such as images, sounds, video, form fields, references to other HTML documents, and basic ASCII data. HTML documents are located by URLs.

• Images— The J2EE platform supports both the GIF (Graphics Interchange Format), and JPEG (Joint Photographic Experts Group) images.

• Class files— The format of a compiled Java file into a bytecode format.

• JAR files— A platform-independent file format (compressed files) that permits many files to be aggregated into one file. Other types of JAR files are Web Archives (WARs), Enterprise Archives (EARs), and Resource Archives (RARs). (See the “Packaging J2EE Applications” section later today for more information.)

• XML documents— A well-formed text-based markup language that is used to define data elements based on a schema. Unlike HTML, XML tags describe the data, rather than the format for displaying it. XML is covered in Appendix C.