/* package whatever; // don't place package name! */
 
import java.util.*;
import java.util.function.*;
import java.util.stream.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
    Stream<String> lines = Stream.of("item1,16,2",
          "item2,17,3",
          "item1,16,5");
    Map<String, List<Integer>> map =
    lines.map(s -> s.split(","))
      .collect(Collectors.toMap(a -> a[0],
          a -> Arrays.asList(a).stream()
           .skip(1).map(Integer::parseInt)
            .collect(Collectors.toList()),
          (a, b) -> {for (int i = 0; i < a.size(); i++) a.set(i, a.get(i) + b.get(i)); return a;}));
System.out.println( map);
 
	}
}

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