/* package whatever; // don't place package name! */
 
import java.math.BigDecimal;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) 
	{
		Map<String, List<BigDecimal>> map = new HashMap<>();
		map.put("k1", Arrays.asList(new BigDecimal(123), new BigDecimal(55)));
		map.put("k2", Arrays.asList(new BigDecimal(123), new BigDecimal(55), new BigDecimal(33)));
		Map<String, BigDecimal> result = map.entrySet().stream()
		        .collect(Collectors.toMap(
		                Map.Entry::getKey,
		                e -> e.getValue().stream().reduce(BigDecimal.ZERO, BigDecimal::add))
		        );
 
		System.out.println(result);
	}
}

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