将LongStream划分为具有最大长度的子流 [英] Divide LongStream into substreams with maximal length

问题描述

我的程序中有一些SQL语句包含带有给定ID的 IN -clauses。问题是在某些情况下可能会有超过1000个ID导致Oracle与ORA-01795崩溃。项目太多。

There are some SQL statements in my program that contain IN-clauses with given Ids. The problem is that in some cases there might be more than 1000 Ids which causes Oracle to crash with ORA-01795. Too many items.

所以我想把这个列表分成多个子列表。

So I want to divide this list into multiple sub-lists.

示例：I有2403个ID

Example: I have 2403 Ids

结果将是三个列表：

1. 0 - 999


2. 1000 - 1999


3. 2000 - 2402

我写了一段有效的代码，但看起来很糟糕。有没有更好的解决方案来解决这个问题？可能与收藏家和收藏家有关groupingby或类似的东西？

I have written a piece of code that works, but looks terrible. Is there any better solution for this problem? Maybe something with Collectors & groupingby or anything like that?

我的代码：

    Map<Integer, List<Long>> result = new HashMap<>();
    ArrayList<Long> asList = new ArrayList<Long>(listOfIds);
    IntStream.range(0, (listOfIds.size() / 1000) + 1)
             .forEach(partGroup -> result.put(partGroup, asList.subList(partGroup * 1000, (partGroup * 1000) + Math.min(1000, 
             asList.size() - partGroup * 1000))));

推荐答案

如果不使用第三方库，我不会认为你可以做得更好。我个人使用这个实用功能，它接近你所做的：

Short of using a third party library I don't think you can do much better. I personally use this utility function, which is close to what you've done:

public static <T> Stream<List<T>> splitListStream(List<T> input, int batchSize) {
  if (batchSize <= 0)
    throw new IllegalArgumentException("batchSize must be positive (" + batchSize + ")");
  if (input.size() <= batchSize) return Stream.of(input);
  return IntStream.range(0, (input.size() + batchSize - 1) / batchSize)
          .mapToObj(i -> {
            int from = i * batchSize;
            int to = Math.min((i + 1) * batchSize, input.size());
            return input.subList(from, to);
          });
}

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