XML allows you to present data in a structured, human-readable form. To display XML from a JSP or servlet, you must use a content type of text/xml instead of text/html. Most modern browsers understand XML and can format it with nice colorized tags or apply XSLT transformations to the data.
Java also supports SAX and DOM parsers that allow you to read XML files and process them either tag-by-tag (SAX) or as a whole document (DOM). In order to ease the burden of writing XML code, JSTL provides tags for parsing, displaying, and transforming XML data.