Create a new list with values from HashMap from existing list

Question

I want to create a new List from Map from existing list.

I got an ArrayList as below structure;

ArrayList
 0 = {LinkedHashMap}
 0 = {LinkedHashMapEntry} "name" --> "value"
 1 = {LinkedHashMapEntry} "surname" --> "value"
 1 = {LinkedHashMap}
 0 = {LinkedHashMapEntry} "name" --> "value"
 1 = {LinkedHashMapEntry} "surname" --> "value"
 ....

What I want to do is get all name values as a new list.

List<String> allNames = ....

Is there any way to get this list with using Java Stream?

Answer 1

Yes:

List<String> allNames =
 list.stream() // this creates a Stream<LinkedHashMap<String,String>>
 .map(m->m.get("name")) // this maps the original Stream to a Stream<String>
 // where each Map of the original Stream in mapped to the
 // value of the "name" key in that Map
 .filter(Objects::nonNull) // this filters out any null values
 .collect(Collectors.toList()); // this collects the elements
 // of the Stream to a List

• Bilbo Baggins: Can you please explain this? I was trying something similar on my IDE but didn't get this .map(m-> m.get("name")) thing. As the list is of Map, won't it pass a map as "m" ?
• Eran: @BilboBaggins see edit. Yes, m's type is Map (or LinkedHashMap, depending on how you declared the input List)
• davidxxx: A side note : filter(Objects::nonNull) is not a requirement.
• Eran: @davidxxx It made sense to me to avoid having nulls in the output List.