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 lt String  String gt  and converting to a Map lt String  AttributeType gt   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 lt String  AttributeType gt  mapConfig Map lt String  String gt  input  String prefix       int subLength   prefix length       return input entrySet   stream   flatMap  Map Entry lt String  Object gt  e  - gt          HashMap lt String  AttributeType gt  r   new HashMap lt  gt           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 lt String  AttributeType gt  mapConfig Map lt String  String gt  input  String prefix       Map lt String  AttributeType gt  result   new HashMap lt  gt         int subLength   prefix length        for Map Entry lt String  String gt  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

User · Accepted Answer

Simply translating the  old for loop way  into streams   private Map lt String  String gt  mapConfig Map lt String  Integer gt  input  String prefix        int subLength   prefix length        return input entrySet   stream                collect Collectors toMap                     entry - gt  entry getKey   substring subLength                       entry - gt  AttributeType GetByName entry getValue

User · Answer

On Java 9 or later  Map entry can be used  so long as you know that neither the key nor value will be null   If either value could legitimately be null  AbstractMap SimpleEntry  as suggested in another answer  or AbstractMap SimpleImmutableEntry would be the way to go   private Map lt String  AttributeType gt  mapConfig Map lt String  String gt  input  String prefix       int subLength   prefix length       return input entrySet   stream   map e - gt         Map entry e getKey   substring subLength   AttributeType GetByName e getValue             collect Collectors toMap Map Entry  getKey  Map Entry  getValue

User · Answer

Please make the following part of the Collectors API    lt K  V gt  Collector lt   super Map Entry lt K  V gt      Map lt K  V gt  gt  toMap       return Collectors toMap Map Entry  getKey  Map Entry  getValue

User · Answer

Question might be a little dated  but you could simply use AbstractMap SimpleEntry lt   as follows   private Map lt String  AttributeType gt  mapConfig      Map lt String  String gt  input  String prefix           int subLength   prefix length           return input entrySet              stream              map e - gt  new AbstractMap SimpleEntry lt  gt                  e getKey   substring subLength                  AttributeType GetByName e getValue                collect Collectors toMap Map Entry  getKey  Map Entry  getValue      any other Pair-like value object would work too  ie  ApacheCommons Pair tuple

User · Answer

Here is a shorter solution by AbacusUtil  Stream of input  toMap e - gt  e getKey   substring subLength                           e - gt  AttributeType GetByName e getValue

[java] Java 8 stream map on entry set

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