OOP Lab 6 - Social Network

(the Italian version is available in file README_it.md).

Develop an application to support a social network. All classes must be in the package social.

The system must use Hibernate ORM to enable persistence of the information. To enable proper testing, the class JPAUtil must be used to retrieve the EntityManager objects via the getEntityManager() method.

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R1 - Subscription

The interaction with the system is made using class Social.

You can register a new account using the method addPerson() which receives as parameters a unique code, name and surname.

The method throws the exception PersonExistsException if the code passed is already associated with a subscription.

The method getPerson() returns a string containing code, name and surname of the person, in order, separated by blanks. If the code, passed as a parameter, does not match any person, the method throws the exception NoSuchCodeException.

💡 Hint:

• use the Person class (already provided) to represent the person
• use the repository pattern (already provided)
  • a PersonRepository class that provides the basic ORM-related operations
  • a personRepository object in the facade class that wraps the collection of Person objects

R2 - Friends

Any person, registered in the social, should have the possibility to add friends. Friendship is bidirectional: if person A is a friend of a person B, that means that person B is a friend of person A.

Friendship is created using method addFriendship() that receives as arguments the codes of both persons. The method throws the exception NoSuchCodeException if one or both codes do not exist.

Method listOfFriends() receives as argument the code of a person and returns the collection of his/her friends. The exception NoSuchCodeException is thrown if the code does not exist. If a person has no friends, an empty collection is returned.

R3 - Groups

It is possible to register a new group using method addGroup(). The name of the group must be unique. A GroupExistsException is thrown if the group name already exists.

The updateGroupName() method allows modifying the name of an existing group. It takes as parameters the current name of the group and the new desired name. A GroupExistsException is thrown if the new group name already exists, and a NoSuchCodeException is thrown if the current group name does not exist.

The deleteGroup() method allows deleting an existing group. It takes the name of the group as a parameter. A NoSuchCodeException is thrown if the group name does not exist.

The method listOfGroups() returns the name list names of all registered groups. If there are no groups in the list, the method should return an empty collection.

A person can subscribe to a group through the method addPersonToGroup() that receives as arguments the code of the person and the name of the group. In case the code of the person, or the name of the group are not found a NoSuchCodeException is thrown.

Method listOfPeopleInGroup() returns the collection codes for the people subscribed to a given group. It returns and empty collection if the group does not exist.

R4 - Statistics

Method personWithLargestNumberOfFriends() returns the code of a person that has the largest number of friends (first level). Do not consider the case of ties.

Method largestGroup() returns the name of the group with the largest number of members. Do not consider the case of ties.

Method personInLargestNumberOfGroups() returns the code of a person that is subscribed to the largest number of groups. Do not consider the case of ties.

R5 - Posts

It is possible to add a new post by a given account using the method post() that accepts as arguments the unique code of the person posting, and the text content. The method returns a unique id for the post containing digits and letters only.

Given a post id it is possible to get:

• the timestamp with getTimestamp(),
• the text content with getPostContent().

The timestamp of the post is the current system time at the moment of the post's creation (retrieved through System.currentTimeMillis()).

The paginated list of all posts from a given user, excluding the user's own posts, can be retrieved using the method getPaginatedUserPosts() that accepts the user id, the page number (1 is the first) and the page length. The method returns the ids of the posts sorted by descending timestamp. The list is split into pages, each containing a number of posts specified by the page length. E.g., if page length is 5 and page is 2, then posts with position 6 to 10 are returned. Post are sorted by descending timestamp, i.e., the most recent first.

The paginated list of all posts from the friends of a given user be retrieved using the method getPaginatedFriendPosts() that accepts the user id, the page number (1 is the first) and the page length. The method works like the previous one, but it returns in the list both the author code and the post id, separated by ":".