Java8 Stream：满足条件后收集元素 [英] Java8 Stream : Collect elements after a condition is met

问题描述

我的POJO如下

class EventUser {
  private id;
  private userId;
  private eventId;
}

我按如下方式检索EventUser对象：

I retrieve EventUser object as follows:

List<EventUser> eventUsers = eventUserRepository.findByUserId(userId);

假设'eventUsers'如下：

Say the 'eventUsers' is as follows:

[
{"id":"id200","userId":"001","eventId":"1010"},
{"id":"id101","userId":"001","eventId":"4212"},
{"id":"id402","userId":"001","eventId":"1221"},
{"id":"id301","userId":"001","eventId":"2423"},
{"id":"id701","userId":"001","eventId":"5423"},
{"id":"id601","userId":"001","eventId":"7423"}
]

使用流式传输，而不使用任何中间变量，如何在给定的EventUser.id之后过滤和收集事件：
ex：

Using streaming, and without using any intermediate variable , how can I filter and collect events after a given EventUser.id: ex:

List<EventUser> filteredByOffSet = eventUsers.stream.SOMEFILTER_AND_COLLECT("id301");

结果应为：

[{"id":"id301","userId":"001","eventId":"2423"},
{"id":"id701","userId":"001","eventId":"5423"},
{"id":"id601","userId":"001","eventId":"7423"}]

推荐答案

在Java 8中，您需要一个有状态过滤器

In Java 8 you need a stateful filter

public static <T> Predicate<T> from(Predicate<T> test) {
    boolean[] found = { false };
    // once found, always true
    return t -> found[0] || (found[0] = test.test(t));
}

注意：这仅对单线程流有意义。

NOTE: this only makes sense for single threaded streams.

List<EventUser> filteredByOffSet = 
     eventUsers.stream()
               .filter(from(e -> "id301".equals(e.getId()))
               .collect(Collectors.toList());

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