Connected application components

src/main/java/de/rwu/easydrop/Main.java

@@ -1,23 +1,8 @@
 package de.rwu.easydrop;
 
-import java.util.List;
-
 import javax.naming.ConfigurationException;
 
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-import org.sqlite.SQLiteDataSource;
-
-import de.rwu.easydrop.api.client.DataSourceFactory;
 import de.rwu.easydrop.core.Core;
-import de.rwu.easydrop.data.connector.AbstractProductPersistence;
-import de.rwu.easydrop.data.connector.SQLiteConnector;
-import de.rwu.easydrop.model.ProductCatalogue;
-import de.rwu.easydrop.service.retriever.CatalogueRetriever;
-import de.rwu.easydrop.service.retriever.ProductRetriever;
-import de.rwu.easydrop.service.writer.CatalogueWriter;
-import de.rwu.easydrop.util.Config;
-import de.rwu.easydrop.util.ProductsConfig;
 
 /**
  * Kickoff point for the service.
@@ -25,11 +10,6 @@ import de.rwu.easydrop.util.ProductsConfig;
  * @since 0.1.0
  */
 public final class Main {
-    /**
-     * Logger for main process.
-     */
-    private static final Logger LOGGER = LoggerFactory.getLogger(Main.class);
-
     /**
      * Prevents unwanted instantiation.
      */
@@ -43,19 +23,6 @@ public final class Main {
      * @param args
      */
     public static void main(final String[] args) throws ConfigurationException {
-        Config config = Config.getInstance();
+        Core.run();
-        ProductsConfig pConfig = ProductsConfig.getInstance();
-        DataSourceFactory dataSourceFactory = new DataSourceFactory(config);
-        ProductRetriever retriever = new ProductRetriever(dataSourceFactory);
-        CatalogueRetriever catRetriever = new CatalogueRetriever(pConfig, retriever);
-        AbstractProductPersistence db = new SQLiteConnector(new SQLiteDataSource());
-        CatalogueWriter catWriter = new CatalogueWriter(db);
-
-        catRetriever.loadCatalogues();
-        List<ProductCatalogue> pCats = catRetriever.getProductCatalogues();
-        catWriter.writeCatalogues(pCats);
-
-        Core core = new Core();
-        core.runCore(pCats);
     }
 }

src/main/java/de/rwu/easydrop/api/client/AmazonProductDataSource.java

@@ -9,6 +9,7 @@ import com.jayway.jsonpath.ReadContext;
 
 import de.rwu.easydrop.api.dto.ProductDTO;
 import de.rwu.easydrop.model.Webshop;
+import de.rwu.easydrop.util.Timestamp;
 
 /**
  * Interface to an Amazon data source.
@@ -61,6 +62,7 @@ public final class AmazonProductDataSource extends AbstractDataSource {
             product.setDeliveryPrice(
                     ctx.read(root + "shippingOptions[0].shippingCost.value.amount", double.class));
             product.setMerchant(ctx.read(root + "merchant.name", String.class));
+            product.setLastUpdate(Timestamp.now());
         } catch (PathNotFoundException e) {
             // Pass, allow incomplete ProductDTO to pass for later validation
         }

src/main/java/de/rwu/easydrop/api/client/DataSourceFactory.java

@@ -2,8 +2,6 @@ package de.rwu.easydrop.api.client;
 
 import javax.naming.ConfigurationException;
 
-import de.rwu.easydrop.data.connector.AbstractProductPersistence;
-import de.rwu.easydrop.exception.PersistenceException;
 import de.rwu.easydrop.util.Config;
 
 /**
@@ -17,17 +15,6 @@ public class DataSourceFactory {
      * The data source config.
      */
     private Config config;
-    /**
-     * Persistence interface.
-     */
-    private AbstractProductPersistence persistence = null;
-
-    /**
-     * @param newPersistence the persistence to set
-     */
-    public void setPersistence(final AbstractProductPersistence newPersistence) {
-        this.persistence = newPersistence;
-    }
 
     /**
      * @param newConfig the config to set
@@ -65,17 +52,4 @@ public class DataSourceFactory {
         String apiKey = config.getProperty("EBAY_API_KEY");
         return new EbayItemDataSource(apiUrl, apiKey);
     }
-
-    /**
-     * Creates a persistence data source.
-     *
-     * @return ProductPersistenceInterface
-     */
-    public AbstractProductPersistence createProductPersistenceDataSource() {
-        if (persistence == null) {
-            throw new PersistenceException("Persistence is not set");
-        }
-
-        return persistence;
-    }
 }

src/main/java/de/rwu/easydrop/api/client/EbayItemDataSource.java

@@ -9,6 +9,7 @@ import com.jayway.jsonpath.ReadContext;
 
 import de.rwu.easydrop.api.dto.ProductDTO;
 import de.rwu.easydrop.model.Webshop;
+import de.rwu.easydrop.util.Timestamp;
 
 /**
  * Interface to an eBay data source.
@@ -70,6 +71,7 @@ public final class EbayItemDataSource extends AbstractDataSource {
             product.setDeliveryPrice(
                     ctx.read(root + "shippingOptions[0].shippingCost.value", double.class));
             product.setMerchant(ctx.read(root + "seller.username", String.class));
+            product.setLastUpdate(Timestamp.now());
         } catch (PathNotFoundException e) {
             // Pass, allow incomplete ProductDTO to pass for later validation
         }

src/main/java/de/rwu/easydrop/api/dto/OfferDTO.java

@@ -1,52 +1,31 @@
 package de.rwu.easydrop.api.dto;
 
 import lombok.Data;
-import de.rwu.easydrop.model.Product;
-import java.util.Date;
 
 /*
- * Offer data transfer object
+ * Offer data transfer object.
+ *
+ * @since 0.3.0
  */
 @Data
 public class OfferDTO {
     /**
-     * Platform internal offer identifier.
+     * ID of the offer, built from identifiers of the source platforms.
      */
     private String offerId;
 
     /**
      * The product that our software buys.
      */
-    private Product sourceProduct;
+    private ProductDTO sourceProduct;
 
     /**
      * The product that our software sells.
      */
-    private Product saleProduct;
+    private ProductDTO targetProduct;
 
     /**
-     * Date of the creation of the offer
+     * Date of last update of the offer.
-     * NOTE: Use Timestamp?
-     * https://docs.oracle.com/javase/8/docs/api/java/sql/Timestamp.html
      */
-    private Date creationDate;
+    private String lastUpdate;
-
-    /**
-     * Date of last update of the offer on the destination website (API).
-     */
-    private Date upDate;
-
-    /**
-     * Date of last check if offer is still valid.
-     */
-    private Date checkDate;
-
-    /**
-     * Creates OfferDTO instance.
-     *
-     * @param newOfferId Internal Offer identifier
-     */
-    public OfferDTO(final String newOfferId) {
-        this.offerId = newOfferId;
-    }
 }

src/main/java/de/rwu/easydrop/api/dto/ProductDTO.java

@@ -40,6 +40,11 @@ public class ProductDTO {
      */
     private boolean available;
 
+    /**
+     * Last update from API.
+     */
+    private String lastUpdate;
+
     /**
      * Creates ProductDTO instance.
      *

src/main/java/de/rwu/easydrop/core/Core.java

@@ -4,42 +4,74 @@ import java.util.List;
 
 import javax.naming.ConfigurationException;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.sqlite.SQLiteDataSource;
+
+import de.rwu.easydrop.api.client.DataSourceFactory;
+import de.rwu.easydrop.data.connector.OfferPersistenceInterface;
+import de.rwu.easydrop.data.connector.ProductPersistenceInterface;
+import de.rwu.easydrop.data.connector.SQLiteConnector;
 import de.rwu.easydrop.model.Offer;
 import de.rwu.easydrop.model.ProductCatalogue;
+import de.rwu.easydrop.service.processing.OfferIdentifier;
+import de.rwu.easydrop.service.processing.OfferProvisioner;
+import de.rwu.easydrop.service.retriever.CatalogueRetriever;
+import de.rwu.easydrop.service.retriever.ProductRetriever;
+import de.rwu.easydrop.service.writer.CatalogueWriter;
+import de.rwu.easydrop.util.Config;
+import de.rwu.easydrop.util.ProductsConfig;
 
 /**
  * The application core.
  *
  * @since 0.3.0
  */
-public class Core {
+public final class Core {
     /**
-     * Offer identifier.
+     * Logging instance.
      */
-    private OfferIdentifier ident;
+    private static final Logger LOGGER = LoggerFactory.getLogger(Core.class);
-    /**
-     * Offer provisioner.
-     */
-    private OfferProvisioner provis;
 
     /**
-     * Constructor.
+     * Hidden Constructor.
-     *
-     * @throws ConfigurationException
      */
-    public Core() throws ConfigurationException {
+    private Core() {
-        this.ident = new OfferIdentifier();
+        // Hidden constructor
-        this.provis = new OfferProvisioner();
-
     }
 
     /**
      * Runs the core.
      *
-     * @param pCats
+     * @throws ConfigurationException
      */
-    public void runCore(final List<ProductCatalogue> pCats) {
+    public static void run() throws ConfigurationException {
+        LOGGER.info("Loading config...");
+        Config config = Config.getInstance();
+        ProductsConfig pConfig = ProductsConfig.getInstance();
+
+        LOGGER.info("Preparing...");
+        DataSourceFactory dataSourceFactory = new DataSourceFactory(config);
+        ProductPersistenceInterface pdb = new SQLiteConnector(new SQLiteDataSource());
+        OfferPersistenceInterface odb = new SQLiteConnector(new SQLiteDataSource());
+        ProductRetriever retriever = new ProductRetriever(dataSourceFactory, pdb);
+        CatalogueRetriever catRetriever = new CatalogueRetriever(pConfig, retriever);
+        CatalogueWriter catWriter = new CatalogueWriter(pdb);
+
+        LOGGER.info("Loading catalogues");
+        catRetriever.loadCatalogues();
+        List<ProductCatalogue> pCats = catRetriever.getProductCatalogues();
+        catWriter.writeCatalogues(pCats);
+
+        LOGGER.info("Creating offers");
+        OfferIdentifier ident = new OfferIdentifier();
         List<Offer> identifiedOffers = ident.runIdentifier(pCats);
+        OfferProvisioner provis = new OfferProvisioner(odb);
         provis.runProvisioner(identifiedOffers);
+
+        // LOGGER.info("Creating transactions");
+        // TODO: Transactions
+
+        LOGGER.info("Done!");
     }
 }

src/main/java/de/rwu/easydrop/core/OfferIdentifier.java

@@ -1,83 +0,0 @@
-package de.rwu.easydrop.core;
-
-import javax.naming.ConfigurationException;
-import java.util.List;
-import java.util.ArrayList;
-import java.util.Date;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
-import de.rwu.easydrop.model.Offer;
-import de.rwu.easydrop.model.ProductCatalogue;
-import de.rwu.easydrop.model.ProductPair;
-import de.rwu.easydrop.service.retriever.OfferRetriever;
-import de.rwu.easydrop.service.processing.OrderManager;
-import de.rwu.easydrop.exception.InvalidCatalogueException;
-
-public class OfferIdentifier {
-    /**
-     * Logger for main process.
-     */
-    private static final Logger LOGGER = LoggerFactory.getLogger(OfferIdentifier.class);
-    /**
-     * OfferRetriever gets the offer from persistence.
-     */
-    private OfferRetriever offerRetriever;
-
-    /**
-     * OfferIdentifier identifies offers that are
-     * feasible to place on a target platform based on
-     * their margin.
-     *
-     * @throws ConfigurationException
-     */
-    public OfferIdentifier() throws ConfigurationException {
-        this.offerRetriever = new OfferRetriever();
-    }
-
-    /**
-     * runIdentifier calls the price function that decides
-     * if it is feasible to dropship products and if so,
-     * at which margin.
-     *
-     * @param pCats
-     * @return newOffers
-     */
-    public List<Offer> runIdentifier(final List<ProductCatalogue> pCats) {
-        List<Offer> identifiedOffers = new ArrayList<>();
-        for (ProductCatalogue pCat : pCats) {
-            try {
-                // Call price finder for all catalogue
-                ProductPair pair = OrderManager.getHighestMarginProducts(pCat);
-                Offer possibleOffer = new Offer();
-                possibleOffer.setCheckDate(new Date());
-                possibleOffer.setSourceProduct(pair.getProduct1());
-                possibleOffer.setSaleProduct(pair.getProduct2());
-                identifiedOffers.add(possibleOffer);
-                LOGGER.info(
-                        "Identified offer "
-                                +
-                                pair.getProduct1().getProductId()
-                                +
-                                " -> "
-                                +
-                                pair.getProduct2().getProductId());
-                // Following fields will be set if offer confirmed
-                // creationDate, offerId
-                // Following fields will be set if offer needs update
-                // upDate
-            } catch (InvalidCatalogueException e) {
-                // if no margin, getHighestMarginProducts will throw
-                System.out.print("product has no margin");
-            }
-        }
-        List<Offer> newOffers = new ArrayList<>();
-        for (Offer identifiedOffer : identifiedOffers) {
-            boolean isNew = true;
-            if (isNew) {
-                newOffers.add(identifiedOffer);
-            }
-        }
-        return newOffers;
-    }
-}

src/main/java/de/rwu/easydrop/core/OfferReviewer.java

@@ -1,81 +0,0 @@
-package de.rwu.easydrop.core;
-
-import de.rwu.easydrop.model.Offer;
-import de.rwu.easydrop.model.Product;
-
-import java.util.List;
-import java.sql.Connection;
-import java.sql.DriverManager;
-import java.sql.ResultSet;
-import java.sql.SQLException;
-import java.sql.Statement;
-import java.util.ArrayList;
-import java.util.Date;
-
-public class OfferReviewer {
-
-    /**
-     *  Check all Offers and compare them with the API.
-     * @return list of all items that need to be changed
-     */
-    public List<Offer> checkOffer(/*OfferReader/retriever for database? */) {
-
-        Connection connection = null;
-        Statement statement = null;
-        ResultSet resultSet = null;
-        List<Offer> changedOffers = new ArrayList<>();
-
-         try {
-            // Establish the database connection
-            connection = DriverManager.getConnection("jdbc:sqlite:persistence.db");
-
-            // Create a SQL statement
-            statement = connection.createStatement();
-
-            // Execute the query to retrieve the entries
-            String query = "SELECT sourceProduct, saleProduct, creationDate, upDate, "
-            + "checkDate, offerId FROM table";
-            resultSet = statement.executeQuery(query);
-
-            // Process the retrieved entries
-            while (resultSet.next()) {
-                Product sourceProduct = (Product) resultSet.getObject("sourceProduct");
-                Product saleProduct = (Product) resultSet.getObject("saleProduct");
-                java.sql.Date creationDate = resultSet.getDate("creationDate");
-                Date updateDate = resultSet.getDate("upDate");
-                Date checkDate = resultSet.getDate("checkDate");
-                String offerId = resultSet.getString("offerId");
-
-                // Call the API to get the current price
-                double apiPrice = getPriceFromAPI(sourceProduct);
-
-                // Compare the prices
-                if (saleProduct.getCurrentPrice() != apiPrice) {
-                // Price has changed, create a Product object and add it to the changedProducts list
-                    Offer offer = new Offer();
-                    changedOffers.add(offer);
-                }
-            }
-        } catch (SQLException e) {
-            e.printStackTrace();
-        } finally {
-            try {
-                if (resultSet != null) {
-                    resultSet.close();
-                }
-                if (statement != null) {
-                    statement.close();
-                }
-                if (connection != null) {
-                    connection.close();
-                }
-            } catch (SQLException e) {
-                e.printStackTrace();
-            }
-        }
-        return new ArrayList<Offer>();
-    }
-
-
-
-}

src/main/java/de/rwu/easydrop/core/OfferUpdater.java

@@ -1,110 +0,0 @@
-package de.rwu.easydrop.core;
-
-import java.sql.Connection;
-import java.sql.DriverManager;
-import java.sql.PreparedStatement;
-import java.sql.SQLException;
-import java.util.List;
-import de.rwu.easydrop.model.Offer;
-import de.rwu.easydrop.model.Product;
-
-
-public class OfferUpdater {
-
-    /**
-     * a.
-     */
-    public OfferUpdater() {
-
-      OfferReviewer offerReviewer = new OfferReviewer();
-      List<Offer> changedOffers = offerReviewer.checkOffer();
-    }
-
-    /**
-     * A.
-     * @param offersToUpdate
-     */
-    public void runUpdater(final List<Offer> offersToUpdate) {
-        Connection connection = null;
-        PreparedStatement deleteStatement = null;
-        PreparedStatement insertStatement = null;
-
-        try {
-        // Establish the database connection
-        connection = DriverManager.getConnection("jdbc:sqlite:persistence.db");
-
-        // Disable auto-commit to perform a transaction
-        connection.setAutoCommit(false);
-
-        // Prepare the DELETE statement to remove the existing entries
-        String deleteQuery = "DELETE FROM your_table WHERE product_id = ?";
-        deleteStatement = connection.prepareStatement(deleteQuery);
-
-        // Prepare the INSERT statement to add the new entries
-        String insertQuery = "INSERT INTO your_table (product_id, product_name, price)"
-        + "VALUES (?, ?, ?)";
-        insertStatement = connection.prepareStatement(insertQuery);
-
-        // Retrieve the existing entries from the database
-        List<Product> existingProducts = retrieveExistingProducts(connection);
-
-        // Delete the existing entries that are not present in the changedProducts list
-        for (Product existingProduct : existingProducts) {
-            if (!changedOffers.(existingProduct)) {
-                deleteStatement.setString(1, existingProduct.getProductId());
-                deleteStatement.executeUpdate();
-            }
-        }
-
-        // Insert the new entries or update the existing entries
-        for (Product changedOffers : offersToUpdate) {
-            if (existingProducts.contains(changedOffers)) {
-                // Update the existing entry with the new data
-                // You need to modify the update query and statement based on your requirements
-                // Here's an example of updating the price of an existing entry
-                String updateQuery = "UPDATE table SET currentPrice = ? WHERE offerId = ?";
-                PreparedStatement updateStatement = connection.prepareStatement(updateQuery);
-                updateStatement.setDouble(1, changedOffers.getCurrentPrice());
-                updateStatement.setString(2, changedOffers.getProductId());
-                updateStatement.executeUpdate();
-                updateStatement.close();
-            } else {
-                // Insert the new entry
-                insertStatement.setString(1, changedOffers.getProductId());
-                insertStatement.setString(2, changedOffers.getMerchant());
-                insertStatement.setDouble(3, changedOffers.getCurrentPrice());
-                insertStatement.executeUpdate();
-            }
-        }
-
-        // Commit the transaction
-        connection.commit();
-    } catch (SQLException e) {
-        // Rollback the transaction in case of an exception
-        if (connection != null) {
-            try {
-                connection.rollback();
-            } catch (SQLException rollbackException) {
-                rollbackException.printStackTrace();
-            }
-        }
-        e.printStackTrace();
-    } finally {
-        // Close the resources (deleteStatement, insertStatement, connection) in a finally block
-        try {
-            if (deleteStatement != null) {
-                deleteStatement.close();
-            }
-            if (insertStatement != null) {
-                insertStatement.close();
-            }
-            if (connection != null) {
-                connection.close();
-            }
-        } catch (SQLException e) {
-            e.printStackTrace();
-        }
-    }
-}
-}
-

src/main/java/de/rwu/easydrop/data/connector/AbstractProductPersistence.java

@@ -1,34 +0,0 @@
-package de.rwu.easydrop.data.connector;
-
-import de.rwu.easydrop.api.client.AbstractDataSource;
-import de.rwu.easydrop.api.dto.ProductDTO;
-
-/**
- * Allows connecting to a persistent product data store.
- *
- * @since 0.2.0
- */
-public abstract class AbstractProductPersistence extends AbstractDataSource {
-    /**
-     * Data origin.
-     */
-    public static final String DATA_ORIGIN = "Persistence";
-
-    /**
-     * Writes a ProductDTO to persistence.
-     *
-     * @param dto
-     */
-    public abstract void saveProduct(ProductDTO dto);
-
-    /**
-     * Gets a ProductDTO from persistence.
-     */
-    @Override
-    public abstract ProductDTO getProductDTOById(String productId);
-
-    /**
-     * Deletes all data from persistence.
-     */
-    public abstract void clearData();
-}

src/main/java/de/rwu/easydrop/data/connector/OfferPersistenceInterface.java

@@ -2,13 +2,13 @@ package de.rwu.easydrop.data.connector;
 
 import de.rwu.easydrop.api.dto.OfferDTO;
 
-public abstract class AbstractOfferPersistence {
+public interface OfferPersistenceInterface {
     /**
      * Writes a ProductDTO to persistence.
      *
      * @param dto
      */
-    public abstract void saveOffer(OfferDTO dto);
+    void writeOffer(OfferDTO dto);
 
     /**
      * Gets a OfferDTO from persistence.
@@ -16,10 +16,10 @@ public abstract class AbstractOfferPersistence {
      * @param offerId
      * @return Offer data transfer object
      */
-    public abstract OfferDTO getOfferDTOById(String offerId);
+    OfferDTO getOfferDTOById(String offerId);
 
     /**
      * Deletes all data from persistence.
      */
-    public abstract void clearData();
+    void clearData();
 }

src/main/java/de/rwu/easydrop/data/connector/ProductPersistenceInterface.java

@@ -0,0 +1,30 @@
+package de.rwu.easydrop.data.connector;
+
+import de.rwu.easydrop.api.dto.ProductDTO;
+
+/**
+ * Allows connecting to a persistent product data store.
+ *
+ * @since 0.2.0
+ */
+public interface ProductPersistenceInterface {
+    /**
+     * Writes a ProductDTO to persistence.
+     *
+     * @param dto
+     */
+    void writeProduct(ProductDTO dto);
+
+    /**
+     * Gets a ProductDTO from persistence.
+     *
+     * @param productId Product identifier
+     * @return Product data transfer object
+     */
+    ProductDTO getProductDTOById(String productId);
+
+    /**
+     * Deletes all data from persistence.
+     */
+    void clearData();
+}

src/main/java/de/rwu/easydrop/data/connector/SQLiteConnector.java

@@ -1,6 +1,5 @@
 package de.rwu.easydrop.data.connector;
 
-import java.net.URL;
 import java.sql.Connection;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
@@ -9,6 +8,7 @@ import java.sql.Statement;
 
 import org.sqlite.SQLiteDataSource;
 
+import de.rwu.easydrop.api.dto.OfferDTO;
 import de.rwu.easydrop.api.dto.ProductDTO;
 import de.rwu.easydrop.exception.PersistenceException;
 import de.rwu.easydrop.model.Webshop;
@@ -18,7 +18,8 @@ import de.rwu.easydrop.model.Webshop;
  *
  * @since 0.2.0
  */
-public final class SQLiteConnector extends AbstractProductPersistence {
+public final class SQLiteConnector implements
+        ProductPersistenceInterface, OfferPersistenceInterface {
     /**
      * SQLite Database.
      */
@@ -53,8 +54,8 @@ public final class SQLiteConnector extends AbstractProductPersistence {
             Connection connection = db.getConnection();
 
             // Execute SQL statements to create tables
-            Statement statement = connection.createStatement();
+            Statement createProducts = connection.createStatement();
-            statement.execute(
+            createProducts.execute(
                     "CREATE TABLE IF NOT EXISTS products ("
                             + "dataOrigin TEXT, "
                             + "productId TEXT, "
@@ -62,12 +63,29 @@ public final class SQLiteConnector extends AbstractProductPersistence {
                             + "merchant TEXT, "
                             + "deliveryPrice REAL, "
                             + "available INT, "
-                            + "lastupdate TEXT, "
+                            + "lastUpdate TEXT, "
                             + "UNIQUE(productId, dataOrigin) ON CONFLICT REPLACE"
                             + ")");
 
-            // Close the statement and connection
+            // Close the statement
-            statement.close();
+            createProducts.close();
+
+            Statement createOffers = connection.createStatement();
+            createOffers.execute(
+                    "CREATE TABLE IF NOT EXISTS offers ("
+                            + "offerId TEXT, "
+                            + "sourceWebshop TEXT, "
+                            + "sourceId TEXT,"
+                            + "sourcePrice REAL, "
+                            + "targetWebshop TEXT, "
+                            + "targetId TEXT, "
+                            + "targetPrice REAL, "
+                            + "lastUpdate TEXT, "
+                            + "UNIQUE(offerId) ON CONFLICT REPLACE"
+                            + ")");
+            createOffers.close();
+
+            // Close the connection
             connection.close();
         } catch (SQLException e) {
             throw new PersistenceException("Something went wrong while initializing SQLite DB", e);
@@ -79,12 +97,12 @@ public final class SQLiteConnector extends AbstractProductPersistence {
      *
      * @param dto
      */
-    public void saveProduct(final ProductDTO dto) {
+    public void writeProduct(final ProductDTO dto) {
         String query = "INSERT INTO products ("
                 + "dataOrigin, productId, currentPrice, merchant, "
-                + "deliveryPrice, available, lastupdate"
+                + "deliveryPrice, available, lastUpdate"
                 + ") VALUES ("
-                + "?, ?, ?, ?, ?, ?, datetime('now', 'localtime')"
+                + "?, ?, ?, ?, ?, ?, ?"
                 + ")";
 
         try (Connection connection = db.getConnection();
@@ -97,6 +115,7 @@ public final class SQLiteConnector extends AbstractProductPersistence {
             statement.setString(++index, dto.getMerchant());
             statement.setDouble(++index, dto.getDeliveryPrice());
             statement.setBoolean(++index, dto.isAvailable());
+            statement.setString(++index, dto.getLastUpdate());
 
             statement.executeUpdate();
         } catch (SQLException e) {
@@ -138,7 +157,7 @@ public final class SQLiteConnector extends AbstractProductPersistence {
     public void clearData() {
         try (Connection connection = db.getConnection();
                 Statement statement = connection.createStatement()) {
-            String query = "DELETE FROM products";
+            String query = "DELETE FROM products; DELETE FROM offers;";
             statement.executeUpdate(query);
         } catch (SQLException e) {
             throw new PersistenceException("Something went wrong while clearing the database", e);
@@ -146,26 +165,68 @@ public final class SQLiteConnector extends AbstractProductPersistence {
     }
 
     @Override
-    protected Webshop getDataOrigin() {
+    public void writeOffer(final OfferDTO dto) {
-        throw new UnsupportedOperationException(
+        String query = "INSERT INTO offers ("
-                this.getClass().getName() + " doesn't support getDataOrigin");
+                + "offerId, "
+                + "sourceWebshop, sourceId, sourcePrice, "
+                + "targetWebshop, targetId, targetPrice, "
+                + "lastUpdate"
+                + ") VALUES ("
+                + "?, ?, ?, ?, ?, ?, ?, ?"
+                + ")";
+
+        try (Connection connection = db.getConnection();
+                PreparedStatement statement = connection.prepareStatement(query)) {
+            int index = 0;
+            ProductDTO sourceProduct = dto.getSourceProduct();
+            ProductDTO targetProduct = dto.getTargetProduct();
+
+            statement.setString(++index, dto.getOfferId());
+            statement.setString(++index, sourceProduct.getProductId());
+            statement.setString(++index, sourceProduct.getDataOrigin().toString());
+            statement.setDouble(++index, sourceProduct.getCurrentPrice());
+            statement.setString(++index, targetProduct.getProductId());
+            statement.setString(++index, targetProduct.getDataOrigin().toString());
+            statement.setDouble(++index, targetProduct.getCurrentPrice());
+            statement.setString(++index, dto.getLastUpdate());
+
+            statement.executeUpdate();
+        } catch (SQLException e) {
+            throw new PersistenceException("Something went wrong while saving to SQLite", e);
+        }
     }
 
     @Override
-    protected String getApiKey() {
+    public OfferDTO getOfferDTOById(final String offerId) {
-        throw new UnsupportedOperationException(
+        String query = "SELECT * FROM offers WHERE offerId = ?";
-                this.getClass().getName() + " doesn't support getApiKey");
+        OfferDTO dto = null;
+
+        try (Connection connection = db.getConnection();
+                PreparedStatement statement = connection.prepareStatement(query)) {
+
+            statement.setString(1, offerId);
+
+            try (ResultSet resultSet = statement.executeQuery()) {
+                if (resultSet.next()) {
+                    dto = new OfferDTO();
+                    ProductDTO srcProduct = new ProductDTO(
+                            resultSet.getString("sourceId"),
+                            Webshop.fromString(resultSet.getString("sourceWebshop")));
+                    srcProduct.setCurrentPrice(resultSet.getDouble("sourcePrice"));
+                    ProductDTO targetProduct = new ProductDTO(
+                            resultSet.getString("targetId"),
+                            Webshop.fromString(resultSet.getString("targetWebshop")));
+                    srcProduct.setCurrentPrice(resultSet.getDouble("targetPrice"));
+                    dto.setOfferId(resultSet.getString("offerId"));
+                    dto.setSourceProduct(srcProduct);
+                    dto.setTargetProduct(targetProduct);
+                    dto.setLastUpdate(resultSet.getString("lastUpdate"));
+                }
+            }
+        } catch (SQLException e) {
+            throw new PersistenceException("Something went wrong while reading from SQLite", e);
         }
 
-    @Override
+        return dto;
-    protected ProductDTO buildProductDTO(final ProductDTO product, final String json) {
-        throw new UnsupportedOperationException(
-                this.getClass().getName() + " doesn't support buildProductDTO");
-    }
-
-    @Override
-    protected URL createApiUrl(final String productIdentifier) {
-        throw new UnsupportedOperationException(
-                this.getClass().getName() + " doesn't support createApiUrl");
     }
 }

src/main/java/de/rwu/easydrop/exception/InvalidOfferException.java

@@ -0,0 +1,22 @@
+package de.rwu.easydrop.exception;
+
+public class InvalidOfferException extends RuntimeException {
+    /**
+     * Throws an exception that signifies the data of an Offer are invalid.
+     *
+     * @param message
+     */
+    public InvalidOfferException(final String message) {
+        super(message);
+    }
+
+    /**
+     * Throws an exception that signifies the data of an Offer are invalid.
+     *
+     * @param message
+     * @param cause
+     */
+    public InvalidOfferException(final String message, final Throwable cause) {
+        super(message, cause);
+    }
+}

src/main/java/de/rwu/easydrop/model/Offer.java

@@ -1,8 +1,5 @@
 package de.rwu.easydrop.model;
 
-import java.util.Date;
-
-
 import lombok.Data;
 
 /**
@@ -10,9 +7,13 @@ import lombok.Data;
  *
  * @since 0.3.0
  */
-
 @Data
 public class Offer {
+    /**
+     * ID of the offer, built from identifiers of the source platforms.
+     */
+    private String offerId;
+
     /**
      * The product that our software buys.
      */
@@ -21,27 +22,10 @@ public class Offer {
     /**
      * The product that our software sells.
      */
-    private Product saleProduct;
+    private Product targetProduct;
 
     /**
-     * Date of the creation of the offer.
+     * Date of last update of the offer.
-     * NOTE: Use Timestamp? https://docs.oracle.com/javase/8/docs/api/java/sql/Timestamp.html
      */
-    private Date creationDate;
+    private String lastUpdate;
-
-    /**
-     * Date of last update of the offer on the destination website (API).
-     */
-    private Date upDate;
-
-    /**
-     * Date of last check if offer is still valid.
-     */
-    private Date checkDate;
-
-    /**
-     * ID of the offer.
-     */
-    private String offerId;
-
 }

src/main/java/de/rwu/easydrop/model/Product.java

@@ -40,6 +40,11 @@ public class Product {
      */
     private boolean available;
 
+    /**
+     * Last update from API.
+     */
+    private String lastUpdate;
+
     @Override
     public final String toString() {
         return "Product: ["

src/main/java/de/rwu/easydrop/model/ProductCatalogue.java

@@ -68,7 +68,7 @@ public class ProductCatalogue {
     @Override
     public String toString() {
         StringBuilder sb = new StringBuilder();
-        sb.append("Product Catalogue: ").append(productName).append("\n");
+        sb.append("Catalogue Name: ").append(productName).append("\n");
         sb.append("Description: ").append(description).append("\n");
         sb.append("Products:\n");
         for (Product product : products) {

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

@@ -1,7 +1,6 @@
 package de.rwu.easydrop.service.mapping;
 
 import de.rwu.easydrop.api.dto.OfferDTO;
-
 import de.rwu.easydrop.model.Offer;
 
 /**
@@ -31,6 +30,10 @@ public final class OfferMapper {
      */
     public static Offer mapOfferFromDTO(final OfferDTO dto) {
         Offer offer = new Offer();
+        offer.setOfferId(dto.getOfferId());
+        offer.setSourceProduct(ProductMapper.mapProductFromDTO(dto.getSourceProduct()));
+        offer.setTargetProduct(ProductMapper.mapProductFromDTO(dto.getTargetProduct()));
+        offer.setLastUpdate(dto.getLastUpdate());
 
         return offer;
     }
@@ -42,7 +45,11 @@ public final class OfferMapper {
      * @return OfferDTO
      */
     public static OfferDTO mapOfferToDTO(final Offer offer) {
-        OfferDTO dto = new OfferDTO(offer.getOfferId());
+        OfferDTO dto = new OfferDTO();
+        dto.setOfferId(offer.getOfferId());
+        dto.setSourceProduct(ProductMapper.mapProductToDTO(offer.getSourceProduct()));
+        dto.setTargetProduct(ProductMapper.mapProductToDTO(offer.getTargetProduct()));
+        dto.setLastUpdate(offer.getLastUpdate());
 
         return dto;
     }

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

@@ -39,6 +39,7 @@ public final class ProductMapper {
         product.setDeliveryPrice(dto.getDeliveryPrice());
         product.setMerchant(dto.getMerchant());
         product.setProductId(dto.getProductId());
+        product.setLastUpdate(dto.getLastUpdate());
 
         return product;
     }
@@ -56,6 +57,7 @@ public final class ProductMapper {
         dto.setCurrentPrice(product.getCurrentPrice());
         dto.setDeliveryPrice(product.getDeliveryPrice());
         dto.setMerchant(product.getMerchant());
+        dto.setLastUpdate(product.getLastUpdate());
 
         return dto;
     }

src/main/java/de/rwu/easydrop/service/processing/OfferIdentifier.java

@@ -1,56 +1,56 @@
 package de.rwu.easydrop.service.processing;
 
+import java.util.ArrayList;
 import java.util.List;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import de.rwu.easydrop.exception.InvalidCatalogueException;
+import de.rwu.easydrop.exception.InvalidOfferException;
+import de.rwu.easydrop.model.Offer;
 import de.rwu.easydrop.model.Product;
 import de.rwu.easydrop.model.ProductCatalogue;
 import de.rwu.easydrop.model.ProductPair;
 import de.rwu.easydrop.util.FormattingUtil;
+import de.rwu.easydrop.util.Timestamp;
 
-/**
+public class OfferIdentifier {
- * Creates dropshipping orders based on price margin.
+    /**
- *
+     * Logging instance.
- * @since 0.3.0
      */
-public final class OrderManager {
+    private static final Logger LOGGER = LoggerFactory.getLogger(OfferIdentifier.class);
 
     /**
-     * Temporary logging instance.
+     * runIdentifier calls the price function that decides
-     */
+     * if it is feasible to dropship products.
-    private static final Logger LOGGER = LoggerFactory.getLogger(OrderManager.class);
-
-    /**
-     * Private constructor to prevent unwanted instantiation.
      *
-     * @throws UnsupportedOperationException always
+     * @param pCats Product catalogues
+     * @return Identified offers
      */
-    private OrderManager() throws UnsupportedOperationException {
+    public List<Offer> runIdentifier(final List<ProductCatalogue> pCats) {
-        throw new UnsupportedOperationException("This is a stateless class, don't instantiate it.");
+        List<Offer> identifiedOffers = new ArrayList<>();
-    }
-
-    /**
-     * Creates orders for products with sufficient margin.
-     *
-     * @param pCats Product Catalogues
-     */
-    public static void createOrders(final List<ProductCatalogue> pCats) {
         for (ProductCatalogue pCat : pCats) {
-            ProductPair pair = getHighestMarginProducts(pCat);
 
-            // #12: Create actual orders/transactions, remove logger
+            // Call price finder for all catalogue
+            ProductPair pair = getHighestMarginProducts(pCat);
+            Offer possibleOffer = new Offer();
+            possibleOffer.setLastUpdate(Timestamp.now());
+            possibleOffer.setSourceProduct(pair.getProduct1());
+            possibleOffer.setTargetProduct(pair.getProduct2());
+            identifiedOffers.add(possibleOffer);
+
             double margin = pair.getProduct2().getCurrentPrice()
                     - pair.getProduct1().getCurrentPrice();
             String marginFormatted = FormattingUtil.formatEuro(margin);
-            LOGGER.info("{}: Margin {} ({} to {})",
+            LOGGER.info("\n Identified Offer: {} ({} to {}) with margin {} ",
                     pCat.getProductName(),
-                    marginFormatted,
                     pair.getProduct1().getDataOrigin(),
-                    pair.getProduct2().getDataOrigin());
+                    pair.getProduct2().getDataOrigin(),
+                    marginFormatted);
         }
+
+        return identifiedOffers;
     }
 
     /**
@@ -79,7 +79,7 @@ public final class OrderManager {
         }
 
         if (cheapestProduct.getCurrentPrice() == mostExpensiveProduct.getCurrentPrice()) {
-            throw new InvalidCatalogueException("Price margin is zero!");
+            throw new InvalidOfferException("Price margin is zero!");
         }
 
         return new ProductPair(cheapestProduct, mostExpensiveProduct);

src/main/java/de/rwu/easydrop/service/processing/OfferProvisioner.java

@@ -1,15 +1,16 @@
-package de.rwu.easydrop.core;
+package de.rwu.easydrop.service.processing;
 
 import java.util.List;
 
 import de.rwu.easydrop.api.client.AmazonSeller;
 import de.rwu.easydrop.api.client.EbaySeller;
-import de.rwu.easydrop.exception.DataWriterException;
+import de.rwu.easydrop.data.connector.OfferPersistenceInterface;
 import de.rwu.easydrop.model.Offer;
 import de.rwu.easydrop.model.Webshop;
 import de.rwu.easydrop.service.mapping.ProductMapper;
 import de.rwu.easydrop.service.writer.OfferWriter;
 import de.rwu.easydrop.util.Config;
+import de.rwu.easydrop.util.FormattingUtil;
 
 public class OfferProvisioner {
     /**
@@ -31,11 +32,11 @@ public class OfferProvisioner {
     private EbaySeller ebaySeller;
 
     private void toSeller(final Offer offer) throws IllegalArgumentException {
-        if (offer.getSaleProduct().getDataOrigin() == Webshop.eBay) {
+        if (offer.getTargetProduct().getDataOrigin() == Webshop.eBay) {
-            this.ebaySeller.sellProduct(ProductMapper.mapProductToDTO(offer.getSaleProduct()));
+            this.ebaySeller.sellProduct(ProductMapper.mapProductToDTO(offer.getTargetProduct()));
 
-        } else if (offer.getSaleProduct().getDataOrigin().equals(Webshop.Amazon)) {
+        } else if (offer.getTargetProduct().getDataOrigin().equals(Webshop.Amazon)) {
-            this.amazonSeller.sellProduct(ProductMapper.mapProductToDTO(offer.getSaleProduct()));
+            this.amazonSeller.sellProduct(ProductMapper.mapProductToDTO(offer.getTargetProduct()));
         } else {
             throw new IllegalArgumentException("Unsupported target plattform");
         }
@@ -44,10 +45,11 @@ public class OfferProvisioner {
 
     /**
      * Is the class for placing orders on a target platform.
+     *
+     * @param db Persistence Interface
      */
-    public OfferProvisioner(/* OfferWriter for database? */) {
+    public OfferProvisioner(final OfferPersistenceInterface db) {
-
+        this.offerWriter = new OfferWriter(db);
-        this.offerWriter = new OfferWriter();
         this.config = Config.getInstance();
         this.amazonSeller = new AmazonSeller(
                 config.getProperty("AMAZON_API_URL"),
@@ -63,27 +65,17 @@ public class OfferProvisioner {
      * @param offersToProvision
      */
     public final void runProvisioner(final List<Offer> offersToProvision) {
-
         for (Offer newOffer : offersToProvision) {
+            String newOfferId = FormattingUtil.removeSpaces(
+                    newOffer.getSourceProduct().getDataOrigin().toString()
+                            + newOffer.getTargetProduct().getDataOrigin().toString()
+                            + "_"
+                            + newOffer.getSourceProduct().getProductId()
+                            + newOffer.getTargetProduct().getProductId());
 
-            try {
             this.toSeller(newOffer);
-                // if successfully transmitted
+            newOffer.setOfferId(newOfferId);
-                // add to persistence
-                // "duplicate" the product with dataOrigin new platform and merchant = "me"
-                try {
             offerWriter.writeOfferToPersistence(newOffer);
-                } catch (Exception e) {
-                    System.out.println("Could not write to persistence");
-                }
-            } catch (IllegalArgumentException e) {
-                System.out.println(
-                        "Offer could not be placed, "
-                                + newOffer.getSaleProduct().getDataOrigin()
-                                + " is not supported");
-            } catch (DataWriterException e) {
-                System.out.println("could not transmit offer");
-            }
         }
     }
 }

src/main/java/de/rwu/easydrop/service/retriever/CatalogueRetriever.java

@@ -5,6 +5,9 @@ import java.util.List;
 
 import javax.naming.ConfigurationException;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import de.rwu.easydrop.model.Product;
 import de.rwu.easydrop.model.ProductCatalogue;
 import de.rwu.easydrop.util.ProductsConfig;
@@ -17,6 +20,11 @@ import lombok.Data;
  */
 @Data
 public class CatalogueRetriever {
+    /**
+     * Logging instance.
+     */
+    private static final Logger LOGGER = LoggerFactory.getLogger(CatalogueRetriever.class);
+
     /**
      * User-configured products.
      */
@@ -56,15 +64,14 @@ public class CatalogueRetriever {
                     pCat.getProductName(), pCat.getDescription());
 
             for (Product product : pCat.getProducts()) {
-                Product newProduct = new Product();
+                Product newProduct = productRetriever.getProductFromWebshop(product.getDataOrigin(),
-
-                newProduct = productRetriever.getProductFromWebshop(product.getDataOrigin(),
                         product.getProductId());
 
                 newProductCatalogue.addProduct(newProduct);
             }
 
             productCatalogues.add(newProductCatalogue);
+            LOGGER.info("\nLoaded Catalogue: \n" + newProductCatalogue.toString());
         }
     }
 }

src/main/java/de/rwu/easydrop/service/retriever/OfferRetriever.java

@@ -1,5 +1,40 @@
 package de.rwu.easydrop.service.retriever;
 
-public class OfferRetriever {
+import de.rwu.easydrop.api.dto.OfferDTO;
+import de.rwu.easydrop.data.connector.OfferPersistenceInterface;
+import de.rwu.easydrop.model.Offer;
+import de.rwu.easydrop.service.mapping.OfferMapper;
 
+/**
+ * Retrieves offer information from different sources.
+ *
+ * @since 0.3.0
+ */
+public class OfferRetriever {
+    /**
+     * Persistence interface.
+     */
+    private OfferPersistenceInterface persistence;
+
+    /**
+     * Creates an Offer Retriever.
+     *
+     * @param db Persistence Interface
+     */
+    public OfferRetriever(final OfferPersistenceInterface db) {
+        this.persistence = db;
+    }
+
+    /**
+     * Retrieves an offer from persistence.
+     *
+     * @param offerId
+     * @return Offer from persistence
+     */
+    public Offer getOfferFromPersistence(final String offerId) {
+        OfferPersistenceInterface src = persistence;
+
+        OfferDTO dto = src.getOfferDTOById(offerId);
+        return OfferMapper.mapOfferFromDTO(dto);
+    }
 }

src/main/java/de/rwu/easydrop/service/retriever/ProductRetriever.java

@@ -4,7 +4,7 @@ import de.rwu.easydrop.api.client.AmazonProductDataSource;
 import de.rwu.easydrop.api.client.DataSourceFactory;
 import de.rwu.easydrop.api.client.EbayItemDataSource;
 import de.rwu.easydrop.api.dto.ProductDTO;
-import de.rwu.easydrop.data.connector.AbstractProductPersistence;
+import de.rwu.easydrop.data.connector.ProductPersistenceInterface;
 import de.rwu.easydrop.model.Product;
 import de.rwu.easydrop.model.Webshop;
 import de.rwu.easydrop.service.mapping.ProductMapper;
@@ -20,19 +20,20 @@ public class ProductRetriever {
      * Data source factory.
      */
     private DataSourceFactory dataSourceFactory;
-
     /**
-     * @param newDataSourceFactory the WebshopFactory to set
+     * Persistence interface.
      */
-    public void setWebshopFactory(final DataSourceFactory newDataSourceFactory) {
+    private ProductPersistenceInterface persistence;
-        this.dataSourceFactory = newDataSourceFactory;
-    }
 
     /**
      * @param newDataSourceFactory
+     * @param newPersistence
      */
-    public ProductRetriever(final DataSourceFactory newDataSourceFactory) {
+    public ProductRetriever(
-        this.setWebshopFactory(newDataSourceFactory);
+            final DataSourceFactory newDataSourceFactory,
+            final ProductPersistenceInterface newPersistence) {
+        this.dataSourceFactory = newDataSourceFactory;
+        this.persistence = newPersistence;
     }
 
     /**
@@ -74,9 +75,7 @@ public class ProductRetriever {
      * @return Product from persistence
      */
     public Product getProductFromPersistence(final String productId) {
-        AbstractProductPersistence src = dataSourceFactory.createProductPersistenceDataSource();
+        ProductDTO dto = persistence.getProductDTOById(productId);
-
-        ProductDTO dto = src.getProductDTOById(productId);
         Product product = ProductMapper.mapProductFromDTO(dto);
         ProductValidator.validate(product);
 

src/main/java/de/rwu/easydrop/service/validation/OfferValidator.java

@@ -1,5 +1,6 @@
 package de.rwu.easydrop.service.validation;
 
+import de.rwu.easydrop.exception.InvalidOfferException;
 import de.rwu.easydrop.model.Offer;
 
 /**
@@ -16,13 +17,19 @@ public final class OfferValidator {
     private OfferValidator() throws UnsupportedOperationException {
         throw new UnsupportedOperationException("This is a validator class, don't instantiate it.");
     }
+
     /**
      * Makes sure an Offer does not contain invalid information.
      *
      * @param offer the Offer
      */
-    public static void validate(final Offer offer) { }
+    public static void validate(final Offer offer) {
+        try {
+            if (offer.getOfferId().equals("")) {
+                throw new InvalidOfferException("Offer ID cannot be empty");
+            }
+        } catch (NullPointerException e) {
+            throw new InvalidOfferException("Required information is missing in the offer", e);
+        }
+    }
 }
-
-
-

src/main/java/de/rwu/easydrop/service/writer/CatalogueWriter.java

@@ -3,7 +3,7 @@ package de.rwu.easydrop.service.writer;
 import java.util.List;
 
 import de.rwu.easydrop.api.dto.ProductDTO;
-import de.rwu.easydrop.data.connector.AbstractProductPersistence;
+import de.rwu.easydrop.data.connector.ProductPersistenceInterface;
 import de.rwu.easydrop.model.Product;
 import de.rwu.easydrop.model.ProductCatalogue;
 import de.rwu.easydrop.service.mapping.ProductMapper;
@@ -18,14 +18,14 @@ public final class CatalogueWriter {
     /**
      * Holds a persistence reference.
      */
-    private AbstractProductPersistence persistence;
+    private ProductPersistenceInterface persistence;
 
     /**
      * Creates new instance.
      *
      * @param newPersistence
      */
-    public CatalogueWriter(final AbstractProductPersistence newPersistence) {
+    public CatalogueWriter(final ProductPersistenceInterface newPersistence) {
         persistence = newPersistence;
     }
 
@@ -40,7 +40,7 @@ public final class CatalogueWriter {
                 ProductValidator.validate(product);
                 ProductDTO dto = ProductMapper.mapProductToDTO(product);
 
-                persistence.saveProduct(dto);
+                persistence.writeProduct(dto);
             }
         }
     }

src/main/java/de/rwu/easydrop/service/writer/OfferWriter.java

@@ -1,21 +1,20 @@
 package de.rwu.easydrop.service.writer;
 
 import de.rwu.easydrop.api.dto.OfferDTO;
-import de.rwu.easydrop.data.connector.AbstractOfferPersistence;
+import de.rwu.easydrop.data.connector.OfferPersistenceInterface;
 import de.rwu.easydrop.model.Offer;
 import de.rwu.easydrop.service.mapping.OfferMapper;
-import de.rwu.easydrop.service.validation.OfferValidator;
 
 public class OfferWriter {
     /**
      * Persistence.
      */
-    private AbstractOfferPersistence persistence;
+    private OfferPersistenceInterface persistence;
 
     /**
      * @param newPersistence the persistence to set
      */
-    public void setPersistence(final AbstractOfferPersistence newPersistence) {
+    public OfferWriter(final OfferPersistenceInterface newPersistence) {
         this.persistence = newPersistence;
     }
 
@@ -25,9 +24,8 @@ public class OfferWriter {
      * @param offer
      */
     public void writeOfferToPersistence(final Offer offer) {
-        OfferValidator.validate(offer);
         OfferDTO dto = OfferMapper.mapOfferToDTO(offer);
 
-        persistence.saveOffer(dto);
+        persistence.writeOffer(dto);
     }
 }

src/main/java/de/rwu/easydrop/service/writer/ProductWriter.java

@@ -1,7 +1,7 @@
 package de.rwu.easydrop.service.writer;
 
 import de.rwu.easydrop.api.dto.ProductDTO;
-import de.rwu.easydrop.data.connector.AbstractProductPersistence;
+import de.rwu.easydrop.data.connector.ProductPersistenceInterface;
 import de.rwu.easydrop.model.Product;
 import de.rwu.easydrop.service.mapping.ProductMapper;
 import de.rwu.easydrop.service.validation.ProductValidator;
@@ -15,12 +15,12 @@ public class ProductWriter {
     /**
      * Persistence.
      */
-    private AbstractProductPersistence persistence;
+    private ProductPersistenceInterface persistence;
 
     /**
      * @param newPersistence the persistence to set
      */
-    public void setPersistence(final AbstractProductPersistence newPersistence) {
+    public ProductWriter(final ProductPersistenceInterface newPersistence) {
         this.persistence = newPersistence;
     }
 
@@ -33,6 +33,6 @@ public class ProductWriter {
         ProductValidator.validate(product);
         ProductDTO dto = ProductMapper.mapProductToDTO(product);
 
-        persistence.saveProduct(dto);
+        persistence.writeProduct(dto);
     }
 }

src/main/java/de/rwu/easydrop/util/FormattingUtil.java

@@ -37,4 +37,14 @@ public final class FormattingUtil {
     public static String urlEncode(final String str) {
         return str.replace(" ", "+");
     }
+
+    /**
+     * Removes spaces from target string.
+     *
+     * @param str String
+     * @return Space-less string
+     */
+    public static String removeSpaces(final String str) {
+        return str.replace(" ", "");
+    }
 }

src/main/java/de/rwu/easydrop/util/Timestamp.java

@@ -0,0 +1,29 @@
+package de.rwu.easydrop.util;
+
+import java.time.LocalDateTime;
+import java.time.format.DateTimeFormatter;
+
+/**
+ * Serves as a timestamp source.
+ *
+ * @since 0.3.0
+ */
+public abstract class Timestamp {
+    /**
+     * Hidden constructor.
+     */
+    private Timestamp() {
+        // Don't instantiate me!
+    }
+
+    /**
+     * Returns a formatted time string.
+     *
+     * @return String such as "2023-01-01 00:00:00"
+     */
+    public static String now() {
+        LocalDateTime now = LocalDateTime.now();
+        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
+        return now.format(formatter);
+    }
+}