Wrote OfferWriter and following classes to save offers to persistence

src/main/java/de/rwu/easydrop/service/mapping/OfferMapper.java

@@ -0,0 +1,50 @@
+package de.rwu.easydrop.service.mapping;
+
+import de.rwu.easydrop.api.dto.OfferDTO;
+
+import de.rwu.easydrop.model.Offer;
+
+/**
+ * Maps between Offer, OfferDTO and OfferDTO.
+ *
+ * @since 0.2.0
+ *
+ * @see Offer
+ * @see OfferDTO
+ * @see OfferDTO
+ */
+public final class OfferMapper {
+
+    /**
+     * Private constructor to prevent unwanted instantiation.
+     *
+     * @throws UnsupportedOperationException always
+     */
+    private OfferMapper() throws UnsupportedOperationException {
+        throw new UnsupportedOperationException("This is a mapping class, don't instantiate it.");
+    }
+
+    /**
+     * Creates a Offer object from a corresponding DTO.
+     *
+     * @param dto Offer Data Transfer Object
+     * @return Offer
+     */
+    public static Offer mapOfferFromDTO(final OfferDTO dto) {
+        Offer offer = new Offer();
+
+        return offer;
+    }
+
+    /**
+     * Creates an OfferDTO object from a corresponding offer.
+     *
+     * @param Offer offer
+     * @return OfferDTO
+     */
+    public static OfferDTO mapOfferToDTO(final Offer offer) {
+        OfferDTO dto = new OfferDTO(offer.getOfferId());
+
+        return dto;
+    }
+}