Java Code Inside Page Directive

Hello,
I want to use somE Java code inside of my page directive for JSP page
such as:

<%@page contentType="text/html;charset=XXXXX_JAVA_CODE_HERE_XXXXX" %>

XXXXX_JAVA_CODE_HERE_XXXXX should be some string I set dynamically:
public static String = "UTF-8";

Please, recommend a solution. Thanks.

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