Jones Jones - 2 years ago 82
Java Question

Java 8 stream and grouping of list

I have a list of orders and I want to group them by user using Java 8 stream and Collectors.groupingBy: -> order.getUser())

This return a map containing users and the list of orders:

Map<User, List<Order>>

I don't need the entire object User just a field of it username which is a String, so I want to get something like this:

Map<String, List<Order>>

I tried to map the User to the username field using but can't get it right. How can I do this as simply as possible?

Answer Source

You can just use the groupingBy collector with the username instead of the whole User object: -> order.getUser().getUsername())
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