You can try below java wrapper, notification support is there.
https://github.com/sanjivsingh/stackoverflow-java-sdk
For more detail, follow docs https://github.com/sanjivsingh/stackoverflow-java-sdk/wiki
Query Example :
StackExchangeApiQueryFactory queryFactory = StackExchangeApiQueryFactory.newInstance(
applicationKey, accessToken,StackExchangeSite.STACK_OVERFLOW);
// get all notifications
PagedList<Notification> notifications = queryFactory
.newNotificationApiQuery().list();
// get unread notifications
PagedList<Notification> notification1s = queryFactory
.newNotificationApiQuery().listNotificationsUnread();
// get notifications by userId
PagedList<Notification> notification2s = queryFactory
.newNotificationApiQuery().withUserIds(2384778)
.listUserNotifications();