The collector class provides Collectors.groupingBy(keyProvider, downstream) , which you can use to group by a pair of values. To connect the two values, you can use AbstractMap.SimpleEntry or you can implement your own class Pair<T,K> , which represents a pair of two values (it is worth mentioning that you have to implement the hashCode() and equals(object) methods in your Pair class if you want to use it as a key in a hash map). Also, the two values that you want to compose in the key must implement the hashCode() and equals(object) methods - in this case, you should use immutable classes.
All grouping part can be performed:
final Map<Map.Entry<City, String>, List<Man>> groupedByCityAndStreet = people.stream() .collect(Collectors.groupingBy( man -> new AbstractMap.SimpleEntry<>(man.getAddress().getCity(), man.getAddress().getStreet()), Collectors.toList() ));
In this example, I used AbstractMap.SimpleEntry to represent a pair of Country and street. He creates a map where for each key he groups a list of Man objects based on country and street. Below you can find a complete example:
import java.util.AbstractMap; import java.util.Arrays; import java.util.List; import java.util.Map; import java.util.Objects; import java.util.stream.Collectors; public class GroupByTest { public static void main(String[] args) { final List<Man> people = Arrays.asList( new Man(1, "John", "Doe", 20, 0, new Address(new Country("England"), new City("London"), "Test Street 2", 10000)), new Man(2, "Mary", "Smith", 54, 4, new Address(new Country("Germany"), new City("Berlin"), "Maine Strasse 32", 10000)), new Man(3, "James", "Rose", 13, 0, new Address(new Country("England"), new City("London"), "Test Street 2", 10000)), new Man(4, "Vincent", "Dog", 43, 2, new Address(new Country("Germany"), new City("Berlin"), "Volkswagen Platz 31", 10000)), new Man(5, "Arnold", "Smoke", 72, 3, new Address(new Country("Italy"), new City("Rome"), "Pepperoni 31", 10000)), new Man(6, "Katy", "Puppet", 33, 3, new Address(new Country("England"), new City("London"), "Test Street 3", 10000)) ); final Map<Map.Entry<City, String>, List<Man>> groupedByCityAndStreet = people.stream() .collect(Collectors.groupingBy( man -> new AbstractMap.SimpleEntry<>(man.getAddress().getCity(), man.getAddress().getStreet()), Collectors.toList() )); // Print people associated with given city and street to console groupedByCityAndStreet.forEach((k, v) -> { System.out.println("People associated with " + k.getKey().name + ", " + k.getValue() + ":"); v.forEach(man -> { System.out.println(man); }); }); } static final class Man { private final int id; private final String firstName; private final String lastName; private final int age; private final int countOfChildren; private final Address address; public Man(int id, String firstName, String lastName, int age, int countOfChildren, Address address) { this.id = id; this.firstName = firstName; this.lastName = lastName; this.age = age; this.countOfChildren = countOfChildren; this.address = address; } public int getId() { return id; } public String getFirstName() { return firstName; } public String getLastName() { return lastName; } public int getAge() { return age; } public int getCountOfChildren() { return countOfChildren; } public Address getAddress() { return address; } @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Man man = (Man) o; return id == man.id && age == man.age && countOfChildren == man.countOfChildren && Objects.equals(firstName, man.firstName) && Objects.equals(lastName, man.lastName) && Objects.equals(address, man.address); } @Override public int hashCode() { return Objects.hash(id, firstName, lastName, age, countOfChildren, address); } @Override public String toString() { return "Man{" + "id=" + id + ", firstName='" + firstName + '\'' + ", lastName='" + lastName + '\'' + ", age=" + age + ", countOfChildren=" + countOfChildren + ", address=" + address + '}'; } } static class Address { private final Country country; private final City city; private final String street; private final long quantityOfPeople; public Address(Country country, City city, String street, long quantityOfPeople) { this.country = country; this.city = city; this.street = street; this.quantityOfPeople = quantityOfPeople; } public Country getCountry() { return country; } public City getCity() { return city; } public String getStreet() { return street; } public long getQuantityOfPeople() { return quantityOfPeople; } @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Address address = (Address) o; return quantityOfPeople == address.quantityOfPeople && Objects.equals(country, address.country) && Objects.equals(city, address.city) && Objects.equals(street, address.street); } @Override public int hashCode() { return Objects.hash(country, city, street, quantityOfPeople); } @Override public String toString() { return "Address{" + "country=" + country + ", city=" + city + ", street='" + street + '\'' + ", quantityOfPeople=" + quantityOfPeople + '}'; } } static class City { private final String name; public City(String name) { this.name = name; } public String getName() { return name; } @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; City city = (City) o; return Objects.equals(name, city.name); } @Override public int hashCode() { return Objects.hash(name); } @Override public String toString() { return "City{" + "name='" + name + '\'' + '}'; } } static class Country { private final String name; public Country(String name) { this.name = name; } public String getName() { return name; } @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Country country = (Country) o; return Objects.equals(name, country.name); } @Override public int hashCode() { return Objects.hash(name); } @Override public String toString() { return "Country{" + "name='" + name + '\'' + '}'; } } }
When running this example, the console will have something like this:
People associated with Rome, Pepperoni 31: Man{id=5, firstName='Arnold', lastName='Smoke', age=72, countOfChildren=3, address=Address{country=Country{name='Italy'}, city=City{name='Rome'}, street='Pepperoni 31', quantityOfPeople=10000}} People associated with London, Test Street 3: Man{id=6, firstName='Katy', lastName='Puppet', age=33, countOfChildren=3, address=Address{country=Country{name='England'}, city=City{name='London'}, street='Test Street 3', quantityOfPeople=10000}} People associated with Berlin, Volkswagen Platz 31: Man{id=4, firstName='Vincent', lastName='Dog', age=43, countOfChildren=2, address=Address{country=Country{name='Germany'}, city=City{name='Berlin'}, street='Volkswagen Platz 31', quantityOfPeople=10000}} People associated with Berlin, Maine Strasse 32: Man{id=2, firstName='Mary', lastName='Smith', age=54, countOfChildren=4, address=Address{country=Country{name='Germany'}, city=City{name='Berlin'}, street='Maine Strasse 32', quantityOfPeople=10000}} People associated with London, Test Street 2: Man{id=1, firstName='John', lastName='Doe', age=20, countOfChildren=0, address=Address{country=Country{name='England'}, city=City{name='London'}, street='Test Street 2', quantityOfPeople=10000}} Man{id=3, firstName='James', lastName='Rose', age=13, countOfChildren=0, address=Address{country=Country{name='England'}, city=City{name='London'}, street='Test Street 2', quantityOfPeople=10000}}
Hope this helps.