public static String getSuffix(String fileName) {
        return fileName.substring(fileName.lastIndexOf('.') + 1);
    }
@Test
    void getSuffix() {
        String fileName = "file_name.model_json";
        String expected = "model_json";
        String source = fileName;
        assertThat(FileNameUtils.getSuffix(source)).isEqualTo(expected);
        source = File.separator + "dir" + File.separator + fileName;
        assertThat(FileNameUtils.getSuffix(source)).isEqualTo(expected);
    }