Here is an example of using the SimpleKeyDeserializers class from the Jackson databind package in Java:

import com.fasterxml.jackson.databind.KeyDeserializer;
import com.fasterxml.jackson.databind.deser.SimpleKeyDeserializers;

public class MySimpleKeyDeserializers extends SimpleKeyDeserializers {
    private static final long serialVersionUID = 1L;

    public MySimpleKeyDeserializers() {
        // Add custom key deserializers here
        addDeserializer(MyKey.class, new MyKeyDeserializer());
    }

    private static class MyKeyDeserializer extends KeyDeserializer {
        @Override
        public Object deserializeKey(String key, DeserializationContext ctxt) {
            // Implement deserialization logic here
            // ...
        }
    }
}

You can use this custom key deserializers class by registering it with the ObjectMapper:

ObjectMapper mapper = new ObjectMapper();
mapper.setKeyDeserializers(new MySimpleKeyDeserializers());

This creates a custom key deserializer for the MyKey class, which can be used to define custom deserialization logic for map keys when they are of the MyKey type.

Note that this is useful when you have a custom class that you want to use as a key in Map object but it's not a basic type like String, Integer, etc.