Java 8 使用 2 个字段排序
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Java 8 Sort using 2 fields
提问by Bharathiraja S
Based one some conditions, I have read data from MongoDB and creating a List<Document>
with resultset.
基于一些条件,我已经从 MongoDB 读取数据并创建了一个List<Document>
结果集。
List<Document> documentList = new ArrayList<Document>();
Sample Record Looks like:
示例记录看起来像:
documentList: [
Document{
{ _id=5975ff00a213745b5e1a8ed9,
u_id=,
visblty = 1,
c_id=5975ff00a213745b5e1a8ed8,
batchid=null,
pdate=Tue Jul 11 17:52:25 IST 2017,
locale=en_US,
subject = "Document2"
} },
Document{
{ _id=597608aba213742554f537a6,
u_id=,
visblty = 1,
c_id=597608aba213742554f537a3,
batchid=null,
pdate=Fri Jul 28 01:26:22 IST 2017,
locale=en_US,
subject = "Document2"
} }
]
Using this documentList, again i am filtering using some conditions and then I need to sort the filter record based on some conditions (which I will get in request).
使用此文档列表,我再次使用某些条件进行过滤,然后我需要根据某些条件(我将在请求中获得)对过滤器记录进行排序。
List<Document> outList = documentList.stream()
.filter(d -> d.getInteger("visblty") == 1
&& (!StringUtils.isEmpty(req.pdate())? (d.getDate(CommonConstants.PDATE).after(afterDate)): true)
&& (!StringUtils.isEmpty(req.pdate())? (d.getDate(CommonConstants.PDATE).before(beforeDate)): true)
.sorted().skip(4).limit()
.collect(Collectors.toList());
Not sure how to sorted (Dynamically needs to change the sorting order based on input, it looks like "pdate by DESC
" or "subject by ASC"
)
不确定如何排序(动态需要根据输入更改排序顺序,它看起来像 " pdate by DESC
" 或 " subject by ASC"
)
Like: "order by pdate DESC" or "order by pdate ASC"" or "order by subject DESC"
喜欢: "order by pdate DESC" or "order by pdate ASC"" or "order by subject DESC"
How to sort using Comparator object of Document class.
如何使用 Document 类的 Comparator 对象进行排序。
Note: I have tried couple of method which was suggested by the folks, but I didn't get any luck yet. Thank you in advance!
注意:我尝试了人们建议的几种方法,但我还没有运气。先感谢您!
回答by KayV
You can use group comparator and parallel stream as follows:
您可以按如下方式使用组比较器和并行流:
List<Document> outList = documentList.stream()
.filter(....)
.sorted(Comparator.comparing(Document::getPdate)
.thenComparing(Document::getSubject))
.parallel();
回答by M. Prokhorov
In terms of Java code, equivalent sorting comparators look like the following:
在 Java 代码方面,等效排序比较器如下所示:
order by pdate
Is represented by
Comparator.comparing(Document::getPDate)
order by subject
Is represented by
Comparator.comparing(Document::getSubject)
order by pdate, subject
Is represented by:
Comparator.comparing(Document::getPDate).thenComparing(Document::getSubject)
order by pdate
由
Comparator.comparing(Document::getPDate)
order by subject
由
Comparator.comparing(Document::getSubject)
order by pdate, subject
代表为:
Comparator.comparing(Document::getPDate).thenComparing(Document::getSubject)
If at any point you need to have descending order, you can call reversed()
on comparator, like this:
如果在任何时候您需要降序,您可以调用reversed()
比较器,如下所示:
Comparator.comparing(Document::getPDate).reversed()
.thenComparing(Comparator.comparing(Document::getSubject).reversed())
Note, that thenComparing
method is overridden, providing ability to pass in:
请注意,该thenComparing
方法被覆盖,提供了传入的能力:
- a Comparator
- a Function-extractor (works if whatever function extracts is-a
Comparable
) - a Function and a Comparator(for when extracted value is not itself a
Comparable
, so you cannot use its natural order and have to specify how it should be compared.
- 比较器
- a Function-extractor (如果任何函数提取 is-a 则工作
Comparable
) - 一个函数和一个比较器(因为当提取的值本身不是 a
Comparable
,所以你不能使用它的自然顺序,必须指定它应该如何比较。
回答by Szymon Stepniak
Instead of .sorted()
try using .sorted(Comparator comparator)
method.
而不是.sorted()
尝试使用.sorted(Comparator comparator)
方法。
You can create the Comparator
used with .sorted(comparator)
by using Comparator.comparing()
:
您可以通过使用创建Comparator
used with :.sorted(comparator)
Comparator.comparing()
Comparator.comparing(Function keyExtractor)
.reversed()
.thenComparing(Function keyExtractor)
for example:
例如:
List<Document> outList = documentList.stream()
// do your filtering here
.sorted(Comparator.comparing(Document::getPdate).reversed()
.thenComparing(Document::getSubject))
.skip(4)
.limit()
.collect(Collectors.toList());
In this example you can use method reference Document::getPdate
and Document::getSubject
instead of lambda expression like d -> d.getPdate()
and d -> d.getSubject()
在这个例子中,你可以使用方法引用Document::getPdate
,Document::getSubject
而不是像d -> d.getPdate()
和这样的 lambda 表达式d -> d.getSubject()