code: private void evaluateExpressions() throws JspException {
          if (dataSourceEL != null) {
              dataSource = ExpressionEvaluatorManager.evaluate
                      ("dataSource", dataSourceEL, Object.class, this, pageContext);
          }
  
          if (driverClassNameEL != null) {
              driverClassName = (String) ExpressionEvaluatorManager.evaluate
                      ("driver", driverClassNameEL, String.class, this, pageContext);
          }
  
          if (jdbcURLEL != null) {
              jdbcURL = (String) ExpressionEvaluatorManager.evaluate
                      ("url", jdbcURLEL, String.class, this, pageContext);
          }
  
          if (userNameEL != null) {
              userName = (String) ExpressionEvaluatorManager.evaluate
                      ("user", userNameEL, String.class, this, pageContext);
          }
  
          if (passwordEL != null) {
              password = (String) ExpressionEvaluatorManager.evaluate
                      ("password", passwordEL, String.class, this, pageContext);
          }
      }
docs: Evaluates expressions as necessary