Most elegant way to join a Map to a String in Java 8

Question

I love Guava, and I\'ll continue to use Guava a lot. But, where it makes sense, I try to use the \"new stuff\" in Java 8 instead.

\"Problem\"

Answer 1

 public static void main(String[] args) {


        HashMap<String,Integer> newPhoneBook = new HashMap(){{
            putIfAbsent("Arpan",80186787);
            putIfAbsent("Sanjay",80186788);
            putIfAbsent("Kiran",80186789);
            putIfAbsent("Pranjay",80186790);
            putIfAbsent("Jaiparkash",80186791);
            putIfAbsent("Maya",80186792);
            putIfAbsent("Rythem",80186793);
            putIfAbsent("Preeti",80186794);

        }};


        /**Compining Key and Value pairs and then separate each pair by some delimiter and the add prefix and Suffix*/
        String keyValueCombinedString = newPhoneBook.entrySet().stream().
                map(entrySet -> entrySet.getKey() + ":"+ entrySet.getValue()).
                collect(Collectors.joining("," , "[","]"));
        System.out.println(keyValueCombinedString);

        /**
         *  OUTPUT : [Kiran:80186789,Arpan:80186787,Pranjay:80186790,Jaiparkash:80186791,Maya:80186792,Sanjay:80186788,Preeti:80186794,Rythem:80186793]
         *
         * */


        String keyValueCombinedString1 = newPhoneBook.entrySet().stream().
                map(Objects::toString).
                collect(Collectors.joining("," , "[","]"));
        System.out.println(keyValueCombinedString1);

        /**
         * Objects::toString method concate key and value pairs by =
         * OUTPUT : [Kiran=80186789,Arpan=80186787,Pranjay=80186790,Jaiparkash=80186791,Maya=80186792,Sanjay=80186788,Preeti=80186794,Rythem=80186793]
         * */

    }

> Blockquote

Answer 2

You can grab the stream of the map's entry set, then map each entry to the string representation you want, joining them in a single string using Collectors.joining(CharSequence delimiter).

import static java.util.stream.Collectors.joining;

String s = attributes.entrySet()
                     .stream()
                     .map(e -> e.getKey()+"="+e.getValue())
                     .collect(joining("&"));

But since the entry's toString() already output its content in the format key=value, you can call its toString method directly:

String s = attributes.entrySet()
                     .stream()
                     .map(Object::toString)
                     .collect(joining("&"));