public int readStringsMap(DataInput in, Map<String, Set<String>> map) throws IOException {
        Map<String, Set<String>> result = (Map<String, Set<String>>) readObject(in);
        if (result == null) return 0;
        map.putAll(result);
        return result.size();
    }
Reads a Map of String key and Set of Strings value pairs.

@param in the input stream.
@param map a Map of String key and Set of Strings value pairs.
@return number of elements added to the collection.
@throws IOException if an error occurs.
xmppserver/src/main/java/org/jivesoftware/util/cache/DefaultExternalizableUtil.java