如何在Java流中处理时将列表细分为多个列表？ [重复]

Question

这个问题在这里已有答案：

• Is there a common Java utility to break a list into batches? 13个答案
• Split list into multiple lists with fixed number of elements in java 8 6个答案

我有以下API调用

cloudwatchClient.deleteInsightRules(
    new DeleteInsightRulesRequest().withRuleNames(existingRuleNames));

因为失败了

 [exec] Exception in thread "main" com.amazonaws.services.cloudwatch.model.MissingRequiredParameterException: BATCH_REQUEST_TOO_LARGE: Batch size cannot exceed 20 items. (Service: AmazonCloudWatch; Status Code: 400; Error Code: MissingRequiredParameterException; Request ID: 0f820dc2-38b8-11e9-8465-3718764429f1)

现在我知道我必须多次调用blackTun的20个块中的deleteInsight规则。

所以从概念上讲我正在寻找

existingRuleNames
   .stream().
   .chunkIntoSizeOf(20)          // This is an imaginary method, i need to convert it into something concrete
   .foreach(chunk -> cloudwatchClient.deleteInsightRules(
        new DeleteInsightRulesRequest().withRuleNames(chunk));

现在我无法在java 8 streams api中找到任何东西，它允许我将我的列表分成块并处理成块。有点像scala分组功能Split list into multiple lists with fixed number of elements。

任何人都可以帮我解决这个问题吗？谢谢。我当然可以使用命令式样式并使用子列表，但如果可以，我宁愿避免使用。

Answer 1

在下面的forEach中，您可以使用块执行任何操作：

//my list of 30 strings that needs to be processed (existingRuleNames in your case):
List<String> list = IntStream.range(0, 30).mapToObj(String::valueOf).collect(Collectors.toList());

AtomicInteger prev = new AtomicInteger(0);
IntStream.range(1, (int) (20 * (Math.ceil(Math.abs(list.size() / 20.0)))))
        .filter(i -> i % 20 == 0 || i == list.size())
        .forEach(i -> {
            List<String> chunk = list.subList(prev.get(), i);
            System.out.println("Processing " + chunk);
            prev.set(i);
        });

输出：

Processing [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
Processing [20, 21, 22, 23, 24, 25, 26, 27, 28, 29]

---

所以你的代码应该是这样的：

List<String> existingRuleNames = ...;

AtomicInteger prev = new AtomicInteger(0);
IntStream.range(1, (int) (20 * (Math.ceil(Math.abs(existingRuleNames.size() / 20.0)))))
        .filter(i -> i % 20 == 0 || i == existingRuleNames.size())
        .forEach(i -> {
            List<String> chunk = existingRuleNames.subList(prev.get(), i);
            cloudwatchClient.deleteInsightRules(
                    new DeleteInsightRulesRequest().withRuleNames(chunk));
            prev.set(i);
        });