import java.util.*;
import static java.util.stream.Collectors.*;
class Ideone {
public static void main (String[] args) {
List<Map<String, List<String>>> list =new ArrayList();
Map<String, List<String>> map1 =new HashMap();
List<String> values =new ArrayList();
values.add("TEST");
values.add("TEST1");
map1.put("level",values);
Map<String, List<String>> map2 =new HashMap();
List<String> values2 =new ArrayList();
values2.add("TEST2");
values2.add("TEST3");
map2.put("level",values2);
list.add(map1);
list.add(map2);

List<String> allValues = list.stream() // a stream of Maps
  .map(Map::values) // a stream of Collection<List<String>>
  .flatMap(Collection::stream) // a stream of List<String>
  .flatMap(List::stream) // a stream of String
  .collect(toList());

System.out.println(allValues);
} }