The JSTL (JavaServer Pages Standard Tag Library) fmt tag library provides a set of tags for formatting and internationalizing data in JSP (JavaServer Pages) pages. One of the tags in the fmt tag library is the <fmt:requestEncoding> tag, which is used to set the character encoding of the request.

The <fmt:requestEncoding> tag is used to set the character encoding of the request to ensure that the server can properly interpret the incoming data. The tag should be placed at the top of the JSP page, before any data is sent to the server. The syntax of the tag is as follows:

<fmt:requestEncoding value="characterEncoding" />

where characterEncoding is the name of the character encoding to use.

For example, to set the character encoding of the request to UTF-8, you would use the following tag:

<fmt:requestEncoding value="UTF-8" />

This tag sets the character encoding of the request to UTF-8.

Note that the fmt tag library must be imported at the beginning of the JSP page using the following tag:

<%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt" %>

This imports the fmt tag library and assigns it a prefix of fmt.