[java] Joining a List<String> inside a map

0 Answers

Simply use String.join, no need to create the nested stream:

Map<String, String> result = map.entrySet()
                                e -> e.getKey(), 
                                e -> String.join("|", e.getValue())));

I'm trying to convert a Map<String, List<String>> to a Map<String, String>, where the value for each key is the joint string built by joining all the values in the List in the previous map, e.g.:

A -> ["foo", "bar", "baz"]
B -> ["one", "two", "three"]

should be converted to

A -> "foo|bar|baz"
B -> "one|two|three"

What's the idiomatic way to do this using the Java 8 Streams API?