How to match objects from list with data from map with condition and save to another map using Java 8 Streams

jhenya-d :

Looking for solution how to match objects from list with data from map with condition if object field starts with map values and save to another map

i have map with some data

Map<String, String> dataMap = new HashMap()
    dataMap.put("d1", "DATA1")
    dataMap.put("d2", "DATA2")
    dataMap.put("d3", "DATA3")

and list of DataElement objects

    List<DataElement> elements = new ArrayList()

elements.add(new DataElement("TEXT1"))
elements.add(new DataElement("TEXT2"))
elements.add(new DataElement("DATA1_text1"))
elements.add(new DataElement("DATA2_text2"))


class DataElement {
            public field;


        public DataElement(String text){
            this.field = text
        }

        public getField(){
            return this.field
        }


    }

And i'am trying to get new Map where keys are values from first map and values are objects(field) from List with condition if object field starts with map value: Result should be:

[d1=DATA1_text1, d2=DATA2_text2]

My code:

    Map<String, String> collect2 = dataMap.entrySet().stream()
            .filter({ map -> elements.stream()
                                .anyMatch({ el -> el.getField().startsWith(map.getValue()) })})
            .collect(Collectors.toMap(KEY, VALUE))

Eran :

Hopefully I got the question right:

Map<String, String> collect2 = 
    dataMap.entrySet()
          .stream()
          .map(e -> elements.stream()
                            // this will search for the first element of the List matching
                            // the value of the current Entry, if exists
                            .filter(el -> el.getField().startsWith(e.getValue()))
                            .findFirst()
                            // this will create a new Entry having the original key and the
                            // value obtained from the List
                            .map(el -> new SimpleEntry<>(e.getKey(),el.getField()))
                            // if findFirst found nothing, map to a null element
                            .orElse(null))
          .filter(Objects::nonNull) // filter out all the nulls
          .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));

You are processing the entries of the input Map, and keep only entries having a value that matches an element of the List (via filter(), though you have some syntax errors), but you need to map the input entries into new entries that contain the desired new value.

This above code produces the Map