How to conditionally insert a Map into a list in Java if the list does not already include a map containing a key value pair

I have a list of HashMap objects in Java.
I would like to conditionally add more HashMap objects to this list if the list does not already contain a HashMap having the same key value pair as in the new HashMap.

Here is an example HashMap list. Note that in reality, there are more keys. Here, I am just including "contact_id" for simplicity.

[{contact_id=16247115}, {contact_id=16247116}, {contact_id=16247117}, {contact_id=16247118}, {contact_id=16247119}]

Adding {contact_id=16247117} to this list should not be allowed.
Adding {contact_id = 74857983}, should be allowed.

Ideally, I would like to be able to conditionally add several HashMaps into this list in one line of code. If I were not to perform the conditional check, I could just use the syntax listname.addAll(batchOfHashMaps). I'd like to do something similar, but precluding redundant HashMaps in the list.

What is the most efficient way to achieve this conditional insert in Java?

I reckon there must be a more efficient solution than evaluating each element in the list inside a for-loop.

If you are only wanting to look at one key-value pair of the maps as an identifier, then you could use a Map instead of a List to hold everything. For example,
Map<String, Map<String, String> mapOfMaps;

Then you could add one like:

mapOfMaps.putIfAbsent(mapToAdd.get("contact_id"), mapToAdd);

you could add multiple like:

batchOfHashMaps.forEach(m -> mapOfMaps.putIfAbsent(m.get("contact_id"), m));

To get a collection of your maps simply call values()

mapOfMaps.values();