java object数组转成string数组

  private String[] getIndexNamesByTime(TraceLogRequestDto t, String indexName) {
        String startTime = ();
        String endTime = ();
        List<String> days = (startTime, endTime);
        //得到 索引类型为 log-trace-2019-01-02
        List<String> indexNames = ().map(m ->  indexName+"-"+ m ).collect(());
        //默认包含indexName
        (indexName);
        String[] res = (String[]) (new String[()]);
        return res;
    }