java key value store with extra functionality

We want a java class developed that is a (syncronizable) key-value store. This shall be backed by a an in memory datastore (hashmap?, arraylist? ) of objects with the following properties - key (string) - value (string) - sync_state (int) - timestamp (TIMESTAMP (long?)) - is_deleted (boolean) For this we want a 'class' that implements the following methods: setItem(key, value) - add or update the value identified by key. - set sync_state=1 - new items get NULL or zero for timestamp, removeItem(key) - set is_deleted=true for item - set sync_state=1 getItem(key) - return value of item - if item is_deleted this is the same as if the item doesn't exist getItems() - return array of key, value pairs - if item is_deleted = 1 then do not include item - return empty array if no items defined In addition for synchronizing this key-value store we need: getChanges - return an object with { maxTimestamp: (the max value of all timestamps in the database) items: [ {key: ..., value: ..., timestamp: ..., is_deleted: ... }, {key: ..., value: ..., timestamp: ..., is_deleted: ... }, {key: ..., value: ..., timestamp: ..., is_deleted: ... }, {key: ..., value: ..., timestamp: ..., is_deleted: ... }, ... etc ... ]} - items are all objects in the map with sync_state=1 updateChanges(arrayOfNewAndChangedItems) - the argument arrayOfNewAndChangedItems is a list of {key: ..., value: ..., timestamp: ..., is_deleted: ... } - these should update existing items based on key or add new items. sync_state is set to 0.