How could I import a XSL dynamically?

Hello everybody,

 I need to do this:
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform";>
  <xsl:import href="/recursos/propios/plantillas/xsl/opciones.xsl" />
  <xsl:import href="{$ESTILOS_XSL}" />
  <xsl:param name="ESTILOS_XSL"/>
...

  Is to say, I need that the import was dynamic. I have this error:

com.s2k.control.ExcepcionControlador: javax.servlet.ServletException:
javax.xml.transform.TransformerConfigurationException:
javax.xml.transform.TransformerException:
javax.xml.transform.TransformerException: Could not resolve entity reference:
"{$ESTILOS_XSL}"

  I have a JSP, that whit jstl tags made a transform, but this transform depends
of a variable.

  Could I do this with XSL? What could I do to implement this funcionallity?

  A lot of thanks,

    Marcial Atienzar

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