Question

What happens when headers are repeated in a .jsp you include in another .jsp?

For example if example.jsp starts with this:

<?xml version="1.0" encoding="UTF-8"?>
<jsp:root version="2.0" xmlns:jsp="http://java.sun.com/JSP/Page">
<jsp:directive.page contentType="text/html; charset=UTF-8" />

<div class="content">

<jsp:include page="support.jsp"/>
...

(it includes support.jsp)

And then support.jsp starts also with this:

<?xml version="1.0" encoding="UTF-8"?>
<jsp:root version="2.0" xmlns:jsp="http://java.sun.com/JSP/Page">
<jsp:directive.page contentType="text/html; charset=UTF-8" />
... 

Is that a problem? Is it bad practice?

What does concretely happen when you repeat several times a header that only corresponds to one header in the resulting .html page?

Answer 1

From JSP Specification:

JSP.5.4 <jsp:include>

…

An included page cannot change the
response status code or set headers.
This precludes invoking methods like
setCookie. Attempts to invoke these
methods will be ignored. The
constraint is equivalent to the one
imposed on the include method of the
RequestDispatcher class.

That is, attempt to set content type will be ignored.