Write a utility to flat a Given data structure of Input Map<Key,Object> to Output Map<String,String>.

The Key in the input Map is a String,
The Value in the Input Map can be a String or anothee Map<String,Object>

Example

Given the following map:

{
"customer": { // i.e Map<"customer",custObject>
"id": "123", // i.e Map<"Id","123">
"firstname": "Yem",
"lastname": "Huynh",
"address": {
"address1": "199 Fremont",
"address2": "4th Floor",
"city": "San Francisco",
"state": "CA",
"zip": "94105",
"digitalAddress": {
"email": "abc@def.com
}
}
},
"order": { // i.e Map<"order",orderObject>
"id": "456",
"productId": "789",
"totalCost": "154.76"
}
}

Flatten it into a map where the keys in the map represent the concatenation of the field names that represent the full path to the field value:
{
"customer.id" : "123"
"customer.firstname" : "Yem"
..
..
"customer.address.address1" : "199 Fremont"
"customer.address.address2" : "4th Floor"
"customer.address.digitalAddress.email" : "abc@def.com"
..
..
"order.id" : "456"
}

PS ebay asked me this question twice