DOCBOOK: inserting an external source code example into xml docbook

hi,

I would ask someone how can I insert a source code from an external entity 
directly in the the xml book without typing it, or copy/paste it.
For example I would todo something like

<!ENTITY example01 SYSTEM "example01.txt">

<para>
	<example>
		<title>a little example</title>
	&example01;
	</example>
</para>

The problem is that I would to avoid the problem of parsing < and & characters 
that exists in example01.txt, so if I use <![CDATA[ &example01; ]]> I cannot 
solve in this case the problem, because I have &example01; literally and not 
the &example01 entity itself.

some suggestion ?

thanks
Lore