This example will show how to convert a java.util.stream.Stream into a Map in Java 8. A Collector is a reduction operation that will accumulate elements from a stream into a cumulative result. We must supply a Collector to gather the Stream’s items into Map which we can do by using a connivence method toMap() from the Collectors utility. The first parameter required by toMap is a function that defines the key. It asks, what value in the object will be the key in the map. The second value is a value mapper which will provide the value to the map.