I have a `Map<String, String>` the `String` key is nothing but numeric value like "123" etc. I'm getting numeric value because this values are coming from the UI in my JSF component. I don't want to change the contract of UI component.   

Now I would like to create a `Map<Long, String>` based on the above `Map`, I saw some `transform` methods in the `Maps` class but all are focusing on the converting value and not key.   

Is there any better way to convert `Map<String, String>` to `Map<Long, String>` ?