1 工具类

@Slf4j
public class Recost {

    //重算费请求接口
    private static final String URL = "https://xxx/xxx/xxx/reComCost";
    //算费接口请求头设置：token ------- 使用时替换生产用户登录的token
    private static final String HEADER_AUTHTOKEN = "263464be9c924309af15b7ec21d87739";
    //算费接口请求头设置：路由
    private static final String HEADER_ROUTENAME = "sendWaybillSite";

    //几个线程并发执行
    //所有运单号分成几组执行
    private static final int SPLIT_LEN = 6;
    //每次算费运单个数
    private static final int WAYBILL_COST_SIZE = 250;

    //读取的文件名  ------- 放resources目录下
    private static final String FILE_NAME = "waybillno.txt";

    private static ExecutorService executorService = Executors.newFixedThreadPool(SPLIT_LEN);

    public static void main(String[] args) {
        try {
            long l1 = System.currentTimeMillis();
            List<String> waybillStrList = loadWaybillNoParams();
            int len = (int) Math.ceil((double) waybillStrList.size() / SPLIT_LEN);
            List<List<String>> waybillGroupList = groupList(waybillStrList, len);

            List<CompletableFuture<Void>> futureList = new ArrayList<>();
            for (List<String> list : waybillGroupList) {
                CompletableFuture<Void> future = CompletableFuture.runAsync(() -> {
                    for (String waybillStr : list) {
                        String params = "waybillNos=" + waybillStr;
                        String response = sendPost(URL, params);
                        log.info(response);
                    }
                }, executorService);
                futureList.add(future);
            }
            CompletableFuture<Void> futureAll = CompletableFuture.allOf(futureList.stream().toArray(CompletableFuture[]::new));
            futureAll.join();
            long l2 = System.currentTimeMillis();

            log.info("接口耗时：{}", (l2 - l1));

            executorService.shutdown();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    /*
     * List分割
     */
    public static List<List<String>> groupList(List<String> list, int len) {
        List<List<String>> listGroup = new ArrayList<>();
        int listSize = list.size();
        //子集合的长度
        int toIndex = 2;
        for (int i = 0; i < list.size(); i += len) {
            if (i + len > listSize) {
                len = listSize - i;
            }
            List<String> newList = list.subList(i, i + len);
            listGroup.add(newList);
        }
        return listGroup;
    }

    public static List<String> loadWaybillNoParams() throws IOException, URISyntaxException {
        List<String> resultList = new ArrayList<>();
        URI uri = ClassLoader.getSystemResource(FILE_NAME).toURI();
        List<String> list = Files.readAllLines(Paths.get(uri));
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < list.size(); i++) {
            int pos = i + 1;
            sb.append(list.get(i));
            if (pos % WAYBILL_COST_SIZE == 0 || pos == list.size()) {
                resultList.add(sb.toString());
                sb = new StringBuilder();
            } else {
                sb.append(",");
            }
        }
        return resultList;
    }

    /**
     * @param url
     * @param params name1=value1&name2=value2
     * @return
     */
    public static String sendPost(String url, String params) {
        PrintWriter out;
        out = null;
        BufferedReader in = null;
        StringBuilder result = new StringBuilder();
        try {
            URL realUrl = new URL(url);
            // 打开和URL之间的连接
            URLConnection conn = realUrl.openConnection();
            // 设置通用的请求属性
            conn.setRequestProperty("authToken", HEADER_AUTHTOKEN);
            conn.setRequestProperty("routeName", HEADER_ROUTENAME);
            conn.setRequestProperty("accept", "*/*");
            conn.setRequestProperty("connection", "Keep-Alive");
            conn.setRequestProperty("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
            // 发送POST请求必须设置如下两行
            conn.setDoOutput(true);
            conn.setDoInput(true);
            // 获取URLConnection对象对应的输出流
            out = new PrintWriter(conn.getOutputStream());
            // 发送请求参数
            out.print(params);
            // flush输出流的缓冲
            out.flush();
            // 定义BufferedReader输入流来读取URL的响应
            in = new BufferedReader(
                    new InputStreamReader(conn.getInputStream()));
            String line;
            while ((line = in.readLine()) != null) {
                result.append(line);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        //使用finally块来关闭输出流、输入流
        finally{
            try{
                if(out!=null){
                    out.close();
                }
                if(in!=null){
                    in.close();
                }
            }
            catch(IOException ex){
                ex.printStackTrace();
            }
        }
        return result.toString();
    }
}

2 读取文件（示例）

waybillno.txt

abc300006078626
abc300006043651
abc300006201477
abc300006251049