Java12: Teeing collectors

Teeing collector take two different collectors to transform the elements of a Stream and then merge the result.

 

Signature

public static <T,​R1,​R2,​R> Collector<T,​?,​R> teeing​(Collector<? super T,​?,​R1> downstream1, Collector<? super T,​?,​R2> downstream2, BiFunction<? super R1,​? super R2,​R> merger)

 

Type Parameters:

         T - the type of the input elements

         R1 - the result type of the first collector

         R2 - the result type of the second collector

         R - the final result type

Parameters:

         downstream1 - the first downstream collector

         downstream2 - the second downstream collector

         merger - the function which merges two results into the single one

Returns:

a Collector which aggregates the results of two supplied collectors.

 

Example

Following snippet finds minimum and maximum age of employees in a stream.

 

 

employeeAges.stream().collect(teeing(minBy(Integer::compareTo), maxBy(Integer::compareTo), (minAge, maxAge) -> {

         return new EmployeeMinMaxAge(minAge.get(), maxAge.get());

}));

 

Find the below working example.

 

EmployeeMinMaxAge.java

package com.sample.app.model;

public class EmployeeMinMaxAge {
	private int minAge;
	private int maxAge;

	public EmployeeMinMaxAge(int minAge, int maxAge) {
		super();
		this.minAge = minAge;
		this.maxAge = maxAge;
	}

	public int getMinAge() {
		return minAge;
	}

	public void setMinAge(int minAge) {
		this.minAge = minAge;
	}

	public int getMaxAge() {
		return maxAge;
	}

	public void setMaxAge(int maxAge) {
		this.maxAge = maxAge;
	}

	@Override
	public String toString() {
		return "EmployeeMinMaxAge [minAge=" + minAge + ", maxAge=" + maxAge + "]";
	}

}

TeeingExample.java

package com.sample.app.streams;

import static java.util.stream.Collectors.maxBy;
import static java.util.stream.Collectors.minBy;
import static java.util.stream.Collectors.teeing;

import java.util.Arrays;
import java.util.List;

import com.sample.app.model.EmployeeMinMaxAge;

public class TeeingExample {

	public static void main(String args[]) {
		List<Integer> employeeAges = Arrays.asList(19, 23, 44, 35, 36, 65, 50, 43);

		EmployeeMinMaxAge empMinAndMaxAge = employeeAges.stream()
				.collect(teeing(minBy(Integer::compareTo), maxBy(Integer::compareTo), (minAge, maxAge) -> {
					return new EmployeeMinMaxAge(minAge.get(), maxAge.get());
				}));

		System.out.println(empMinAndMaxAge);
	}

}

Output

EmployeeMinMaxAge [minAge=19, maxAge=65]

 

You can download java12 examples from below link.

https://github.com/harikrishna553/java12-demo

 

 

Reference

https://docs.oracle.com/en/java/javase/12/docs/api/java.base/java/util/stream/Collectors.html#teeing(java.util.stream.Collector,java.util.stream.Collector,java.util.function.BiFunction)

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