code: public int doEndTag()
              throws JspException {
          if(_value != null) {
              if(LOGGER.isInfoEnabled() && pageContext.getAttribute(_resultId) != null)
                  LOGGER.info("Overwriting a value in PageContext attribute map with key \"" + _resultId +
                          "\" and object of type \"" + _value.getClass().getName());
  
              pageContext.setAttribute(_resultId, _value);
          }
          else {
              if(LOGGER.isInfoEnabled())
                  LOGGER.info("Removing a value from the PageContext attribute map with key \"" + _resultId +
                          "\".  The object returned by the expression is null.");
  
              pageContext.removeAttribute(_resultId);
          }
  
          localRelease();
          return EVAL_PAGE;
      }
docs: Evaluate the expression at the <code>value</code> attribute and store the result in the
  {@link javax.servlet.jsp.PageContext} under the attribute key specified in {@link #setResultId(String)}.
  If an existing key in the PageContext's attribute map exists, a warning will be written to the log file.
  If errors occur during expression evaluation, they will be reported in the JSP page.  If the value
  returned by the expression is null, an attribute named <code>resultId</code> will be removed from
  the PageContext's attribute map.
  
  @return {@link #EVAL_PAGE}