Collectors collectingAndThen (Collector downstream, Function finisher)
Description
Collectors collectingAndThen(Collector<T,A,R> downstream,
Function<R,RR> finisher)
adapts a Collector
to perform an additional finishing transformation.
Syntax
collectingAndThen
has the following syntax.
public static <T,A,R,RR> Collector<T,A,RR> collectingAndThen(Collector<T,A,R> downstream, Function<R,RR> finisher)
Example
The following example shows how to use collectingAndThen
.
import java.time.LocalDate;
import java.time.Month;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;
import java.util.stream.Collectors;
/*from w w w . j av a 2 s. c o m*/
public class Main {
public static void main(String[] args) {
Map<Month, String> dobCalendar = Employee
.persons()
.stream()
.collect(
Collectors.collectingAndThen(
Collectors.groupingBy(
p -> p.getDob().getMonth(),
Collectors.mapping(Employee::getName,
Collectors.joining(" "))), result -> {
for (Month m : Month.values()) {
result.putIfAbsent(m, "None");
}
return Collections.unmodifiableMap(new TreeMap<>(result));
}));
dobCalendar.entrySet().forEach(System.out::println);
}
}
enum Gender {
MALE, FEMALE
}
class Employee {
private long id;
private String name;
private Gender gender;
private LocalDate dob;
private double income;
public Employee(long id, String name, Gender gender, LocalDate dob,
double income) {
this.id = id;
this.name = name;
this.gender = gender;
this.dob = dob;
this.income = income;
}
public String getName() {
return name;
}
public Gender getGender() {
return gender;
}
public LocalDate getDob() {
return dob;
}
public static List<Employee> persons() {
Employee ken = new Employee(1, "Jame", Gender.MALE, LocalDate.of(1970,
Month.MAY, 4), 6123.0);
Employee jeff = new Employee(2, "Jeff", Gender.MALE, LocalDate.of(1971,
Month.JULY, 5), 7112.0);
Employee donna = new Employee(3, "Jane", Gender.FEMALE, LocalDate.of(1972,
Month.JULY, 9), 8712.0);
Employee chris = new Employee(4, "Jodd", Gender.MALE, LocalDate.of(1973,
Month.DECEMBER, 6), 1823.0);
Employee laynie = new Employee(5, "Janey", Gender.FEMALE, LocalDate.of(
1974, Month.DECEMBER, 3), 1234.0);
Employee lee = new Employee(6, "Jason", Gender.MALE, LocalDate.of(1975,
Month.MAY, 8), 2412.0);
// Create a list of persons
List<Employee> persons = Arrays
.asList(ken, jeff, donna, chris, laynie, lee);
return persons;
}
}
The code above generates the following result.