Convert Collector Results
Description
We can convert the result of the collector to a different type.
collectingAndThen() method of the Collectors class is defined as follows.
collectingAndThen(Collector<T,A,R> downstream, Function<R,RR> finisher)
The first argument is a collector that collects the data. The second argument is a finisher which converts the result.
Example
The following code returns an unmodifiable view of the collected data.
import java.time.LocalDate;
import java.time.Month;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.stream.Collectors;
public class Main {
public static void main(String[] args) {
List<String> names = Employee.persons()
.stream()/*from w w w .ja v a 2s .c o m*/
.map(Employee::getName)
.collect(Collectors.collectingAndThen(Collectors.toList(),
result -> Collections.unmodifiableList(result)));
System.out.println(names);
}
}
class Employee {
public static enum Gender {
MALE, FEMALE
}
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 static List<Employee> persons() {
Employee p1 = new Employee(1, "Jake", Gender.MALE, LocalDate.of(1971,
Month.JANUARY, 1), 2343.0);
Employee p2 = new Employee(2, "Jack", Gender.MALE, LocalDate.of(1972,
Month.JULY, 21), 7100.0);
Employee p3 = new Employee(3, "Jane", Gender.FEMALE, LocalDate.of(1973,
Month.MAY, 29), 5455.0);
Employee p4 = new Employee(4, "Jode", Gender.MALE, LocalDate.of(1974,
Month.OCTOBER, 16), 1800.0);
Employee p5 = new Employee(5, "Jeny", Gender.FEMALE, LocalDate.of(1975,
Month.DECEMBER, 13), 1234.0);
Employee p6 = new Employee(6, "Jason", Gender.MALE, LocalDate.of(1976,
Month.JUNE, 9), 3211.0);
List<Employee> persons = Arrays.asList(p1, p2, p3, p4, p5, p6);
return persons;
}
}
The code above generates the following result.
