Java case-insensitive map with null key [duplicate]

Question

Is there a Map implementation in Java that will use case-insensitive String matching for the key, but also supports the null key? I know that

new TreeMap<String, String>(String.CASE_INSENSITIVE_ORDER)

supports case-insensitive matching of String keys, but it doesn't support the null key.

Answer 1

If you're on Java 8, the following will create a null-compatible, case-insensitive TreeMap:

Comparator<String> cmp = Comparator.nullsFirst(String.CASE_INSENSITIVE_ORDER);
TreeMap<String, String> map = new TreeMap<>(cmp);

No external libraries needed.

Answer 2

You can use CaseInsensitiveMap for this. This will fulfill your requirement. It is case-insensitive as well as supports null keys.

From the doc

A case-insensitive Map. Before keys are added to the map or compared to other existing keys, they are converted to all lowercase in a locale-independent fashion by using information from the Unicode data file.

Null keys are supported.

The keySet() method returns all lowercase keys, or nulls.