Convert String array to Map using Java 8 Lambda expressions

Question

Is there a better functional way of converting an array of Strings in the form of "key:value" to a Map using the Java 8 lambda syntax?

Arrays.asList("a:1.0", "b:2.0", "c:3.0")         .stream()         .map(elem -> elem.split(":")         .collect(Collectors.toMap(keyMapper?, valueMapper?)); 

The solution I have right now does not seem really functional:

Map<String, Double> kvs = new HashMap<>(); Arrays.asList("a:1.0", "b:2.0", "c:3.0")         .stream()         .map(elem -> elem.split(":"))         .forEach(elem -> kvs.put(elem[0], Double.parseDouble(elem[1]))); 

Answer 1

You can modify your solution to collect the Stream of String arrays into a Map (instead of using forEach) :

Map<String, Double> kvs =     Arrays.asList("a:1.0", "b:2.0", "c:3.0")         .stream()         .map(elem -> elem.split(":"))         .collect(Collectors.toMap(e -> e[0], e -> Double.parseDouble(e[1]))); 

Of course this solution has no protection against invalid input. Perhaps you should add a filter just in case the split String has no separator :

Map<String, Double> kvs =     Arrays.asList("a:1.0", "b:2.0", "c:3.0")         .stream()         .map(elem -> elem.split(":"))         .filter(elem -> elem.length==2)         .collect(Collectors.toMap(e -> e[0], e -> Double.parseDouble(e[1]))); 

This still doesn't protect you against all invalid inputs (for example "c:3r" would cause NumberFormatException to be thrown by parseDouble).