java 8流收集最大对象，并按属性区分

Posted 2021-04-21

某些列表在这里

List<Book> list = new ArrayList<>();
{
   list.add(new Book("Core Java", 200));
   list.add(new Book("Core Java", 500));
   list.add(new Book("Core Java", 800));
   list.add(new Book("Learning Freemarker", 150));          
   list.add(new Book("Learning Freemarker", 1350));   
   list.add(new Book("Learning Freemarker", 1250));   
   list.add(new Book("Spring MVC", 300));
   list.add(new Book("Spring MVC", 600)); 
   list.add(new Book("Spring MVC", 1600));
}

我要显示这样的图书清单

Core Java", 800
Learning Freemarker", 1350
Spring MVC", 1600

每个1个元素

list .stream().distinct()
     .sorted(Comparator.comparing(Book::bookname)
     .thenComparing(Book::getPrice)).collect(Collectors.toList());

此代码仅排序。

答案

首先您可以对Book名称进行分组，然后将它们收集到Map<String, List<Book>>中，然后从map.values()中收集每种类型的最高价格书

List<Book> books = list.stream()
                       .collect(Collectors.groupingBy(Book::getName))
                       .values()
                       .stream()
                       .map(book -> book.stream().max(Comparator.comparingInt(Book::getCost)))
                       .filter(Optional::isPresent)
                       .map(Optional::get)
                       .collect(Collectors.toList());