I have List of Objects. Each object holds a List of Long and a List of JsonNode. What I am trying to do is create a third List with Object, wherein each Object is the result of a cross join between the above two Lists.
E.g.
class MyClass{
List<Long> _listLong;
List<JsonNode> _listJsonNode;
}
I have List of MyClass Objects. What I want is to create a List of MyClass.
class MyClass2{
Long id;
JsonNode jsonNode;
}
such that List<MyClass2> holds the result of a cross join of List<Long> and List<JsonNode>.
I am able to do the same using loops. Is there a way to achieve the same using Streams in Java?
If you're starting with a list of MyClass objects, you have to flatten it and use two nested streams for the Cartesian product.
List<MyClass2> result = myClassList.stream().flatMap(
mc -> mc.get_listLong()
.stream()
.flatMap(i -> mc.get_listJsonNode()
.stream()
.map(js -> new MyClass2(i, js))))
.collect(Collectors.toList());
That assumes the constructor MyClass2(Long, JsonNode) exists. The inner flatMap is creating the required Cartesian product, by essentially iterating over all JsonNode elements for each Long element.