如何将Java代码转换为Lambda和Stream实现?

I have an implementation to find duplicate characters in a String:

Map<Character, Integer> charMap = new HashMap<>();
for (int i = 0; i < word.length(); i++) {
    Character ch = word.charAt(i);
    if (charMap.containsKey(ch)) {
        charMap.put(ch, charMap.get(ch) + 1);
    } else {
        charMap.put(ch, 1);
    }
}

I want to know if I can convert this implementation into an Java 8 and Stream implementation. To do something like this:

Map<Character, Integer> charMap = new HashMap<>();

Then convert the String word into a List of characters:

List<Character> chars = word.chars()
        .mapToObj(i -> (char) i)
        .collect(Collectors.toList());

现在要做这样的事情:

chars.stream()
        .filter(e -> charMap.containsKey(e))...

谢谢!