### Question:
DomainUtil { public static String getLowerCaseByLabel(String str) { if (StringUtils.isBlank(str)) { return str; } String[] splits = StringUtils.split(str, "."); StringBuffer result = new StringBuffer(); if (str.startsWith(".")) { str = str.replaceFirst("\\.", ""); result.append("."); } for (String split : splits) { split = getLowercaseIfAllAscii(split); result.append(split); result.append("."); } String resultStr = result.toString(); if (!str.endsWith(".") && resultStr.endsWith(".")) { resultStr = resultStr.substring(0, resultStr.length() - 1); } return resultStr; } private  DomainUtil(); static boolean isArpaTldAndLabelIsValid(String domainName); static boolean validateDomainNameIsValidIdna(String domainName,
            boolean forSearch); static boolean validateSearchStringIsValidIdna(String searchString); static String deleteLastPoint(String paramStr); static String getLowerCaseByLabel(String str); static String safeGeneDomainPunyName(String domainName); static String geneDomainPunyName(String domainName); static String urlDecodeAndReplaceAsciiToLowercase(String str); static String replaceAsciiToLowercase(String str); static String urlDecode(String str); static String iso8859Decode(String str); static boolean isLdh(String domain); static boolean validateSearchLdnName(String searchString); static final String XN_PREFIX; static final String ACE_PREFIX; static final int MAX_DOMAIN_LENGTH_WITHOUT_LAST_DOT; static final int MIN_DOMAIN_LENGTH_WITHOUT_LAST_DOT; static final String ARPA_SUFFIX; static final String IPV4_ARPA_SUFFIX; static final String IPV6_ARPA_SUFFIX; static final int MAX_ASCII_CODE; static final String BLANK_IN_DOMAIN; static final java.lang.String DISALLOWED_DELIMITERS; }### Answer:
@Test public void testGetLowerCaseByLabel() { assertEquals("cnnic.cn", DomainUtil.getLowerCaseByLabel("cnnic.cn")); assertEquals("cnnic.cn", DomainUtil.getLowerCaseByLabel("CNNIC.cn")); assertEquals("cnnic", DomainUtil.getLowerCaseByLabel("CNNIC")); assertEquals("cnnic.cn", DomainUtil.getLowerCaseByLabel("CNNIC.CN")); assertEquals("cnnic.cn", DomainUtil.getLowerCaseByLabel("cNNIC.CN")); assertEquals("cnnic.cn", DomainUtil.getLowerCaseByLabel("cNNIC.cN")); assertEquals("清华TSing.cn", DomainUtil.getLowerCaseByLabel("清华TSing.CN")); }