Ipc Repository structure, including the full jparepository interface, as well as guava's optional in the findOne

IpcCrudRepository.java

package be.ipc.crp.core.repository;

import com.google.common.base.Optional;
import org.springframework.data.repository.NoRepositoryBean;
import org.springframework.data.repository.Repository;

import java.io.Serializable;

@NoRepositoryBean
public interface IpcCrudRepository<T, ID extends Serializable> extends Repository<T, ID> {

    /**
     * Saves a given entity. Use the returned instance for further operations as the save operation might have changed the
     * entity instance completely.
     *
     * @param entity
     * @return the saved entity
     */
    <S extends T> S save(S entity);

    /**
     * Saves all given entities.
     *
     * @param entities
     * @return the saved entities
     * @throws IllegalArgumentException in case the given entity is (@literal null}.
     */
    <S extends T> Iterable<S> save(Iterable<S> entities);

    /**
     * Retrieves an entity by its id.
     *
     * @param id must not be {@literal null}.
     * @return the entity with the given id or {@literal null} if none found
     * @throws IllegalArgumentException if {@code id} is {@literal null}
     */
    Optional<T> findOne(ID id);

    /**
     * Returns whether an entity with the given id exists.
     *
     * @param id must not be {@literal null}.
     * @return true if an entity with the given id exists, {@literal false} otherwise
     * @throws IllegalArgumentException if {@code id} is {@literal null}
     */
    boolean exists(ID id);

    /**
     * Returns all instances of the type.
     *
     * @return all entities
     */
    Iterable<T> findAll();

    /**
     * Returns all instances of the type with the given IDs.
     *
     * @param ids
     * @return
     */
    Iterable<T> findAll(Iterable<ID> ids);

    /**
     * Returns the number of entities available.
     *
     * @return the number of entities
     */
    long count();

    /**
     * Deletes the entity with the given id.
     *
     * @param id must not be {@literal null}.
     * @throws IllegalArgumentException in case the given {@code id} is {@literal null}
     */
    void delete(ID id);

    /**
     * Deletes a given entity.
     *
     * @param entity
     * @throws IllegalArgumentException in case the given entity is (@literal null}.
     */
    void delete(T entity);

    /**
     * Deletes the given entities.
     *
     * @param entities
     * @throws IllegalArgumentException in case the given {@link Iterable} is (@literal null}.
     */
    void delete(Iterable<? extends T> entities);

    /**
     * Deletes all entities managed by the repository.
     */
    void deleteAll();
}

IpcPagingAndSortingRepository.java

package be.ipc.crp.core.repository;

import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.Sort;
import org.springframework.data.repository.NoRepositoryBean;

import java.io.Serializable;
@NoRepositoryBean
public interface IpcPagingAndSortingRepository<T, ID extends Serializable> extends IpcCrudRepository<T, ID> {
    /**
     * Returns all entities sorted by the given options.
     *
     * @param sort
     * @return all entities sorted by the given options
     */
    Iterable<T> findAll(Sort sort);

    /**
     * Returns a {@link org.springframework.data.domain.Page} of entities meeting the paging restriction provided in the {@code Pageable} object.
     *
     * @param pageable
     * @return a page of entities
     */
    Page<T> findAll(Pageable pageable);
}

IpcRepository.java

package be.ipc.crp.core.repository;

import com.google.common.base.Optional;
import org.springframework.data.domain.Sort;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.repository.NoRepositoryBean;
import org.springframework.data.repository.PagingAndSortingRepository;

import java.io.Serializable;
import java.util.List;

/**
 * JPA specific extension of {@link org.springframework.data.repository.Repository}.
 *
 * edit: made sure it's optional instead of an exception
 *
 * @author Oliver Gierke
 */
@NoRepositoryBean
public interface IpcRepository<T, ID extends Serializable> extends IpcPagingAndSortingRepository<T, ID> {
    /*
	 * (non-Javadoc)
	 * @see org.springframework.data.repository.CrudRepository#findAll()
	 */
    List<T> findAll();

    /*
     * (non-Javadoc)
     * @see org.springframework.data.repository.PagingAndSortingRepository#findAll(org.springframework.data.domain.Sort)
     */
    List<T> findAll(Sort sort);

    /*
     * (non-Javadoc)
     * @see org.springframework.data.repository.CrudRepository#findAll(java.lang.Iterable)
     */
    List<T> findAll(Iterable<ID> ids);

    /*
     * (non-Javadoc)
     * @see org.springframework.data.repository.CrudRepository#save(java.lang.Iterable)
     */
    <S extends T> List<S> save(Iterable<S> entities);

    /**
     * Flushes all pending changes to the database.
     */
    void flush();

    /**
     * Saves an entity and flushes changes instantly.
     *
     * @param entity
     * @return the saved entity
     */
    <S extends T> S saveAndFlush(S entity);

    /**
     * Deletes the given entities in a batch which means it will create a single {@link org.springframework.data.jpa.repository.Query}. Assume that we will clear
     * the {@link javax.persistence.EntityManager} after the call.
     *
     * @param entities
     */
    void deleteInBatch(Iterable<T> entities);

    /**
     * Deletes all entites in a batch call.
     */
    void deleteAllInBatch();

    /**
     * Returns a reference to the entity with the given identifier.
     *
     * @param id must not be {@literal null}.
     * @return a reference to the entity with the given identifier.
     * @see javax.persistence.EntityManager#getReference(Class, Object)
     */
    T getOne(ID id);
}