code: private Object evaluateDataSource()
              throws JspException {
          ExpressionHandling expr = new ExpressionHandling(this);
          String dataSource = getDataSource();
          String ds = expr.ensureValidExpression(dataSource, "dataSource", "DataSourceError");
          if (ds == null)
              return null;
  
          /* have a valid expression */
          return expr.evaluateExpression(dataSource, "dataSource", pageContext);
      }
docs: Return the Object that is represented by the specified data source.
  @return Object
  @throws JspException