java collector groupingby code example
Example: java 8 group a collections by 2 property
Map<String, Map<BlogPostType, List>> map = posts.stream()
.collect(groupingBy(BlogPost::getAuthor, groupingBy(BlogPost::getType)));
Map<String, Map<BlogPostType, List>> map = posts.stream()
.collect(groupingBy(BlogPost::getAuthor, groupingBy(BlogPost::getType)));