public String fetchNameServerAddr() {
        try {
            String addrs = this.topAddressing.fetchNSAddr();
            if (!UtilAll.isBlank(addrs)) {
                if (!addrs.equals(this.nameSrvAddr)) {
                    log.info("name server address changed, old=" + this.nameSrvAddr + ", new=" + addrs);
                    this.updateNameServerAddressList(addrs);
                    this.nameSrvAddr = addrs;
                    return nameSrvAddr;
                }
            }
        } catch (Exception e) {
            log.error("fetchNameServerAddr Exception", e);
        }
        return nameSrvAddr;
    }
@Test
    public void assertFetchNameServerAddr() throws NoSuchFieldException, IllegalAccessException {
        setTopAddressing();
        assertEquals(defaultNsAddr, mqClientAPI.fetchNameServerAddr());
    }