public int readStringsMap(DataInput in, Map<String, Set<String>> map) throws IOException {
        return strategy.readStringsMap(in, map);
    }
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/ExternalizableUtil.java