Java 8: How to get a value from a list contained as a map value?

Question

I have the following situation: I have a LinkedHashMap<> where the key type is a String and the values types varies: double, String, LinkedHashMap, etc. I am trying to extract a value from a key of one of the LinkedHashMaps values which are a value of the main map. For example, I'd like to get the result 1 from the following code (obviously it is a mess since it doesn't even compile):

Map<String, Object> input = new HashMap<>();     
input.put("a", "1234");
input.put("b", "2345");
input.put("c", "3456");
input.put("d", new HashMap<String, String>());

HashMap<String, Object> input2 = (HashMap<String, Object>)(input.get("d"));
input2.put("d1", 1);
input2.put("d2", 2);

Optional<Integer> result = input.entrySet().stream()
            .filter(e -> e.getKey().equals("d"))
            .map(Map.Entry::getValue)
            .filter(e -> e.getKey().equals("d1"))
            .findFirst();

Where do I go wrong, and of course, what is the best way to get the result?

Thanks.

Answer 1

Once you use a Map with different value (and even key) types (and worse, nested maps). Then I suggest taking a step back and try to analyse what you've done. It seems that you're way better with a class than a Map. An example with your keys:

class YourClass {
    String a;
    String b;
    String c;
    YourOtherClass d;
}

class YourOtherClass {
    Integer d1;
    Integer d2;
}

I've omitted getters, setters and constructors for simplicity.

You can then create instances of those objects, like this:

YourOtherClass yoc = new YourOtherClass(1, 2);
YourClass yc = new YourClass("1234", "2345", "3456", yoc);

And then call the specific getter to receive a value with typesafety:

String a = yc.getA(); // works
Integer i = yc.getA(); // doesn't work

Or setting a new value via the setter:

yoc.setD1(4); // works
yoc.setD1("4"); // doesn't work