Implementation of counting using group in Java 8

I am looking for the implementation of group by, and then filter it according to the count in the lambda expression

select COUNT(employee_id),department_id  from employee
GROUP BY department_id
HAVING COUNT(employee_id) > 1

Is there a simple implementation of using lambda expressions for this purpose

Solution

You can use the groupingby collector with counting() and collectandthen:

import static java.util.stream.Collectors.collectingAndThen;
import static java.util.stream.Collectors.counting;
import static java.util.stream.Collectors.groupingBy;

...

Map<Long,Long> map = 
    employees.stream()
             .collect(collectingAndThen(groupingBy(Employee::getDeptId,counting()),m -> { m.values().removeIf(v -> v <= 1L); return m; }));

Please note that the variability of the mapping returned by groupingby cannot be guaranteed here, so you can use the overloaded version and provide specific variable instances if necessary