Java 8 使用 2 个字段排序

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：

1. order by pdate

   Is represented by

   Comparator.comparing(Document::getPDate)
   

2. order by subject

   Is represented by

   Comparator.comparing(Document::getSubject)
   

3. order by pdate, subject

   Is represented by:

   Comparator.comparing(Document::getPDate).thenComparing(Document::getSubject)

1. order by pdate

   由

   Comparator.comparing(Document::getPDate)
   

2. order by subject

   由

   Comparator.comparing(Document::getSubject)
   

3. 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 thenComparingmethod 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 Comparatorused with .sorted(comparator)by using Comparator.comparing():

您可以通过使用创建Comparatorused 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::getPdateand Document::getSubjectinstead 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()