How to Convert some custom Map object to LinkedHashMap?

Question

Here is what I'm trying to do.

Map<String, List<Address>> mapObj = someService.getSomeAddress();

Using above call I'm getting mapObj of type Map<String, List<Address>>

And I want to send mapObj as a parameter in a another method (that I cannot change) as a LinkedHashMap<String, List<LinkedHashMap>> which does some further processing.

Is there any way that I can solve this problem without affecting data inside mapObj?

• JB Nizet: Well, yes. You need to create a copy anyway. How an Address becomes a List<LinkedHashMap> is unclear, though. And what the order should be is unclear, too. And the fact that the method cares about the concrete type of the map is a smell, too.

Answer 1

You will need to perform a couple of conversion steps.

1. Convert all Address objects to LinkedHashMap objects.
2. Put all Map entries into a LinkedHashMap object.

For 1st one, you can write a utility method some where that can do this conversion. For example,

public static List<LinkedHashMap> addresstoMap(List<Address> addresses)
{
 List<LinkedHashMap> list = new ArrayList<>();
 for(Address a: addresses){
 LinkedHashMap map = new LinkedHashMap();
 // Add address fields to map here
 list.add(map);
 }
 return list;
}

Then, for the 2nd step, you can do this:

LinkedHashMap<String, List<LinkedHashMap>> map = new LinkedHashMap<?,?>();

iterate through the entry sets of mapObj and put them into the above map object.

for (Map.Entry<String, List<Address>> e : m.entrySet()) {
 map.put(e.getKey(), addresstoMap(e.getValue()));
}

The final map object above will contain the correct representation in the LinkedHashMap<String, List<LinkedHashMap>> datatype.

Hope this helps!