code: public static ExpressionFactory getExpressionFactory(ELContext context) {
          ExpressionFactory result = getContext(context, ExpressionFactory.class);
          if (result == null) {
              result = ExpressionFactory.newInstance();
              context.putContext(ExpressionFactory.class, result);
          }
          return result;
      }
docs: Get an ExpressionFactory instance for the specified context, using {@link ELContext#getContext(Class)}, and
  setting such a context value, if not found, to {@link javax.el.ExpressionFactory#newInstance()}.
  
  @param context
  @return ExpressionFactory