application Context within a TagLib

[info]

Hi,

realy basics! I set some values in the web.xml like this:
.
.
.
<context-param>
 <param-name>server_pfad</param-name>
 <param-value>http://localhost:8080/</param-value>
 <description>Server-Pfad</description>
</context-param>
.
.
.

And now I want to get the values within a TagLib:

.
.
pageContext.out().print(pageContext.getServletContext().getAttribute("server_pfad"));
is null
.
.

Whats wrong??

thanks, Rainer