线程池的使用示例-批量查询

1.使用countDown

public Map<Long, User> batchQueryUserInfo(List<Long> userIds) {
    List<List<Long>> userIdPartitions = Lists.partition(userIds, 50);
    List<User> userList = new ArrayList<>();

    CountDownLatch latch = new CountDownLatch(userIdPartitions.size());
    userIdPartitions.forEach(userIdsPartition -> {
        executorService.submit(()->{
            try {
                List<User> userInfoList = userService.batchQuery(userIdsPartition.stream().map(String::valueOf).collect(Collectors.toList()));
                userList.addAll(userInfoList);
            } catch (Exception e) {
                //log
                return;
            } finally {
                latch.countDown();
            }
        });
    });
    try {
        latch.await(1, TimeUnit.SECONDS);
    } catch (Exception e) {
        //log
    }
    return userList.stream().collect(Collectors.toMap(user -> Long.parseLong(user.getUserId()), v->v));
}

2.Future.get

future.get方法会阻塞，效率不如CountDownLatch。

public Map<Long, User> batchQueryUserInfo(List<Long> empIds) {
    List<List<Long>> userIdPartitions = Lists.partition(userIds, 50);
    List<User> userList = new ArrayList<>();

    List<Future<List<User>>> futureList = new ArrayList<>();
    userIdPartitions.forEach(userIdsPartition -> {
        Future<List<User>> future = executorService.submit(() -> {
            List<User> userInfoList = null;
            try {
                userInfoList = userService.batchQuery(userIdsPartition.stream().map(String::valueOf).collect(Collectors.toList()));
            } catch (Exception e) {
                //log
            }
            return userInfoList;
        });
        futureList.add(future);

    });
    long timeLimit = 1;
    for (Future<List<User>> future : futureList) {
        try {
            userList.addAll(future.get(timeLimit, TimeUnit.MILLISECONDS));
        } catch (Exception e) {
            //log
        }
    }
    return userList.stream().collect(Collectors.toMap(user -> Long.parseLong(user.getUserId()), v->v));
}