Support a wider range of data sources i.e. not just `PreparedStatement`

[donalmurtagh]

Is your feature request related to a problem? Please describe.

Currently, the only way to provide the data for a worksheet is via a PreparedStatement. This is not very convenient for projects that don't use raw SQL or don't use a relational database at all.

Describe the solution you'd like In my specific case, database access is usually one of the following

• A method of a Spring Data JPA repository that defines a JPQL query
• A criteria query

As far as I know, there is no way to get a PreparedStatement from a Spring Data JPA repository method such as this one

public interface UserRepository extends CrudRepository<User, UUID> {

    @Query("""
        from    UserRole ur
        where   ur.role.name = 'SYSTEM_ADMIN'""")
    Collection<UserRole> findAllSysAdmins();
}

In this case, the query is relatively simple, so it would not be too arduous to define a PreparedStatement that executes the equivalent SQL query, but for more complex queries the effort required to translate the JPQL/criteria query into SQL could be considerable.

Although support for JPA queries would solve my problem, perhaps it would be better to consider a type that hides the details of where the data comes from, e.g.

interface WorksheetData {
  /* Provides the labels to be used for the columns in row 1 of the worksheet */
  List<String> columnHeaders()

  /* Provides the values to be shown in rows 2 onwards of the worksheet */
  List<List<Object> cellValues()
}

Then a user could provide their own implementation of this object (instead of a PreparedStatement) which might get the data from a web service, a text file, etc. but MemPOI shouldn't know or care where the data comes from.