java - Java Stream.collect groupingBy和聚合的类

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Java 8 chained method reference?
                                
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                            Comparator.comparing(…) of a nested field
                                
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                                去年关闭。
            
                    
这段代码很简单：

Map<String, List<BlogPost>> postsPerType = posts.stream()
  .collect(groupingBy(BlogPost::getType));

BlogPost在哪里：

class BlogPost {
    String title;
    String author;
    String type;
    int likes;
    // getter setter
}

如果BlogPost还有其他一些类作为字段，而我想按这些字段之一分组，例如

class BlogPost {
    String title;
    String author;
    Description description;
    int likes;
    // getter setter
}

class Description {
    String part1;
    String type;
    // getter setter
}

我该如何说

myBlogPost.getDescription().getType()

在lambda表达式中？

伪代码：

Map<String, List<BlogPost>> postsPerType = posts.stream()
      .collect(groupingBy(BlogPost::getDescription::getType));

编辑：
groupingBy是指：

import static java.util.stream.Collectors.groupingBy;

最佳答案

Map<String, List<BlogPost>> postsPerType = posts.stream()
  .collect(groupingBy(bp -> bp.getDescription().getType()));