Prepare for evaluation of the body. This method is invoked by the JSP page implementation object after setBodyContent and before the first time the body is to be evaluated. This method will not be invoked for empty tags or for non-empty tags whose doStartTag() method returns SKIP_BODY or EVAL_BODY_INCLUDE.
The JSP container will resynchronize any variable values that are indicated as so in TagExtraInfo after the invocation of doInitBody().
@throws JspException
@seealso #doAfterBody