public static String toUnderline(String src, boolean isUpper) {
        return toUnderline(src, '_', isUpper);
    }
@Test
    public void testToUnderline() {
        String result = FieldUtils.toUnderline("ToUnderline", true);
        Assert.assertEquals("TO_UNDERLINE", result);
        String result1 = FieldUtils.toUnderline("ToUnderline", false);
        Assert.assertEquals("to_underline", result1);
    }