You can place any expression within the <%= %> tags and it will be evaluated and displayed as either a String or a numeric type. If you want to call at function that is easy.

<%=func()%>

And you may define the function else where as

<%! String func(){
doSomething();
} %>

Note the explaination mark to indicate that the code is to be placed into the servlet object, and not into straight into the doRequest method.