Split monolithic function

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

@@ -4,6 +4,7 @@ import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.net.HttpURLConnection;
+import java.net.MalformedURLException;
 import java.net.URL;
 
 import org.json.JSONException;
@@ -55,14 +56,7 @@ public final class AmazonProductDataSource implements DataSource {
         ProductDTO product = new ProductDTO(productId, DATA_ORIGIN);
 
         try {
-            URL apiUrl = new URL(
-                    baseUrl
-                            + "/products/2020-08-26/products/"
-                            + productId
-                            + "/offers?productRegion="
-                            + PRODUCT_REGION
-                            + "&locale="
-                            + LOCALE);
+            URL apiUrl = createApiUrl(productId);
 
             HttpURLConnection connection = (HttpURLConnection) apiUrl.openConnection();
             connection.setRequestMethod("GET");
@@ -74,7 +68,7 @@ public final class AmazonProductDataSource implements DataSource {
                 reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
             } else {
                 throw new IllegalArgumentException(
-                        "Amazon API responded with error code " + responseCode);
+                        "Nothing found: Amazon API responded with error code " + responseCode);
             }
 
             String line;
@@ -82,13 +76,25 @@ public final class AmazonProductDataSource implements DataSource {
                 response.append(line);
             }
             reader.close();
+
+            JSONObject offer = new JSONObject(response.toString()).getJSONObject("featuredOffer");
+            buildProductDTO(product, offer);
         } catch (IOException e) {
             throw new IllegalArgumentException("Couldn't fulfill Amazon API request");
         }
 
-        try {
-            JSONObject offer = new JSONObject(response.toString()).getJSONObject("featuredOffer");
+        return product;
+    }
 
+    /**
+     * Enriches a ProductDTO with API-gathered data.
+     *
+     * @param product Unfinished ProductDTO
+     * @param offer   Product data
+     * @return Finished ProductDTO
+     */
+    private ProductDTO buildProductDTO(final ProductDTO product, final JSONObject offer) {
+        try {
             product.setDataOrigin(DATA_ORIGIN);
             product.setAvailable(offer
                     .getString("availability")
@@ -112,4 +118,15 @@ public final class AmazonProductDataSource implements DataSource {
 
         return product;
     }
+
+    @Override
+    public URL createApiUrl(final String productId) throws MalformedURLException {
+        return new URL(baseUrl
+                + "/products/2020-08-26/products/"
+                + productId
+                + "/offers?productRegion="
+                + PRODUCT_REGION
+                + "&locale="
+                + LOCALE);
+    }
 }

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

@@ -1,5 +1,8 @@
 package de.rwu.easydrop.api.client;
 
+import java.net.MalformedURLException;
+import java.net.URL;
+
 import de.rwu.easydrop.api.dto.ProductDTO;
 
 /**
@@ -9,8 +12,17 @@ public interface DataSource {
     /**
      * Retrieves product info from the data source.
      *
-     * @param productId Identifier
+     * @param productId ASIN
      * @return ProductDTO
      */
     ProductDTO getProductDTOById(String productId);
+
+    /**
+     * Creates an URL object to connect to the API with.
+     *
+     * @param productId ASIN
+     * @return URL object
+     * @throws MalformedURLException
+     */
+    URL createApiUrl(String productId) throws MalformedURLException;
 }