Java 8 stream map on entry set

Question

I'm trying to perform a map operation on each entry in a Map object.

I need to take a prefix off the key and convert the value from one type to another. My code is taking configuration entries from a Map<String, String> and converting to a Map<String, AttributeType> (AttributeType is just a class holding some information. Further explanation is not relevant for this question.)

The best I have been able to come up with using the Java 8 Streams is the following:

private Map<String, AttributeType> mapConfig(Map<String, String> input, String prefix) {    int subLength = prefix.length();    return input.entrySet().stream().flatMap((Map.Entry<String, Object> e) -> {       HashMap<String, AttributeType> r = new HashMap<>();       r.put(e.getKey().substring(subLength), AttributeType.GetByName(e.getValue()));       return r.entrySet().stream();    }).collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue)); } 

Being unable to construct an Map.Entry due to it being an interface causes the creation of the single entry Map instance and the use of flatMap(), which seems ugly.

Is there a better alternative? It seems nicer to do this using a for loop:

private Map<String, AttributeType> mapConfig(Map<String, String> input, String prefix) {    Map<String, AttributeType> result = new HashMap<>();     int subLength = prefix.length();     for(Map.Entry<String, String> entry : input.entrySet()) {       result.put(entry.getKey().substring(subLength), AttributeType.GetByName( entry.getValue()));    }    return result; } 

Should I avoid the Stream API for this? Or is there a nicer way I have missed?

Answer 1

Simply translating the "old for loop way" into streams:

private Map<String, String> mapConfig(Map<String, Integer> input, String prefix) {     int subLength = prefix.length();     return input.entrySet().stream()             .collect(Collectors.toMap(                    entry -> entry.getKey().substring(subLength),                     entry -> AttributeType.GetByName(entry.getValue()))); } 

Answer 2

Please make the following part of the Collectors API:

<K, V> Collector<? super Map.Entry<K, V>, ?, Map<K, V>> toMap() {   return Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue); }