Replicating Java 9's Map.of or Guava's ImmutableMap.of in pure Java 8

MapOf.java

// using a coustom keyvalue String per element of the Stream
Map<String, String> map = Stream.of("key1:value1", "key2:value2")
                                .collect(Collectors.toMap(str -> str.split(":")[0],   // key function
                                                          str -> str.split(":")[1])); // value function