java8自定义收集器,Java 8复杂的自定义收集器

最新推荐文章于 2022-06-30 08:00:00 发布

转载最新推荐文章于 2022-06-30 08:00:00 发布 · 58 阅读

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#java8自定义收集器

本文介绍了一种使用StreamEx库的groupRuns方法对流式数据进行分组的技术，特别是针对论坛帖子类数据按时间间隔进行分组的方法。

I have a stream of objects which I would like to collect the following way.

Let's say we are handling forum posts:

class Post {

private Date time;

private Data data

}

I want to create a list which groups posts by a period. If there were no posts for X minutes, create new group.

class PostsGroup{

List posts = new ArrayList<> ();

}

I want to get a List containing the posts grouped by the interval.

example: interval 10 minutes.

posts:

[{time:x, data:{}}, {time:x + 3, data:{}} , {time:x+ 12, data:{}, {time:x + 45, data:{}}}]

I want to get a list of posts group:

[

{posts : [{time:x, data:{}}, {time:x + 3, data:{}}, {time:x+ 12, data:{}]]},

{posts : [{time:x+ 45, data:{}]}

]

notice that the first group lasted till X + 22. Then a new post was received at X + 45.

Is this possible?

解决方案

This problem could be easily solved using the groupRuns method of my StreamEx library:

long MAX_INTERVAL = TimeUnit.MINUTES.toMillis(10);

StreamEx.of(posts)

.groupRuns((p1, p2) -> p2.time.getTime() - p1.time.getTime() <= MAX_INTERVAL)

.map(PostsGroup::new)

.toList();

I assume that you have a constructor

class PostsGroup {

private List posts;

public PostsGroup(List posts) {

this.posts = posts;

}

The StreamEx.groupRuns method takes a BiPredicate which is applied to two adjacent input elements and returns true if they must be grouped together. This method creates the stream of lists where each list represents the group. This method is lazy and works fine with parallel streams.