Abstract the data provider

src/main/java/com/europeanexchangerates/exchangeapi/provider/ExchangeRateProvider.java

@@ -0,0 +1,10 @@
+package com.europeanexchangerates.exchangeapi.provider;
+
+import java.time.LocalDate;
+import java.util.TreeMap;
+
+import com.europeanexchangerates.exchangeapi.dto.ExchangeRate;
+
+public interface ExchangeRateProvider {
+    TreeMap<LocalDate, ExchangeRate> getExchangeRates() throws Exception;
+}

src/main/java/com/europeanexchangerates/exchangeapi/provider/UrlCsvZipExchangeRateProvider.java

@@ -0,0 +1,24 @@
+package com.europeanexchangerates.exchangeapi.provider;
+
+import java.time.LocalDate;
+import java.util.TreeMap;
+
+import com.europeanexchangerates.exchangeapi.dto.ExchangeRate;
+import com.europeanexchangerates.exchangeapi.util.DataDownloader;
+import com.europeanexchangerates.exchangeapi.util.UrlCsvZipDataDownloader;
+
+public class UrlCsvZipExchangeRateProvider implements ExchangeRateProvider {
+    private DataDownloader downloader;
+
+    public UrlCsvZipExchangeRateProvider() {
+        this.downloader = new UrlCsvZipDataDownloader();
+    }
+
+    public UrlCsvZipExchangeRateProvider(DataDownloader downloader) {
+        this.downloader = downloader;
+    }
+
+    public TreeMap<LocalDate, ExchangeRate> getExchangeRates() throws Exception {
+        return downloader.downloadData();
+    }
+}

src/main/java/com/europeanexchangerates/exchangeapi/service/ExchangeRateService.java

@@ -15,8 +15,8 @@
 import com.europeanexchangerates.exchangeapi.dto.CurrencyHighestRate;
 import com.europeanexchangerates.exchangeapi.dto.ExchangeRate;
 import com.europeanexchangerates.exchangeapi.exception.InvalidDateRangeException;
-import com.europeanexchangerates.exchangeapi.util.UrlCsvZipDataDownloader;
-import com.europeanexchangerates.exchangeapi.util.DataDownloader;
+import com.europeanexchangerates.exchangeapi.provider.ExchangeRateProvider;
+import com.europeanexchangerates.exchangeapi.provider.UrlCsvZipExchangeRateProvider;
 
 @Service
 public class ExchangeRateService {
@@ -25,12 +25,12 @@ public class ExchangeRateService {
     private TreeMap<LocalDate, ExchangeRate> exchangeRates;
 
     public ExchangeRateService() throws Exception {
-        DataDownloader downloader = new UrlCsvZipDataDownloader();
-        this.exchangeRates = downloader.downloadData();
+        ExchangeRateProvider provider = new UrlCsvZipExchangeRateProvider();
+        this.exchangeRates = provider.getExchangeRates();
     }
 
-    public ExchangeRateService(DataDownloader downloader) throws Exception {
-        this.exchangeRates = downloader.downloadData();
+    public ExchangeRateService(ExchangeRateProvider provider) throws Exception {
+        this.exchangeRates = provider.getExchangeRates();
     }
 
     /**

src/test/java/com/europeanexchangerates/exchangeapi/service/ExchangeRateServiceTest.java

@@ -26,7 +26,7 @@
 import com.europeanexchangerates.exchangeapi.dto.CurrencyHighestRate;
 import com.europeanexchangerates.exchangeapi.dto.ExchangeRate;
 import com.europeanexchangerates.exchangeapi.exception.InvalidDateRangeException;
-import com.europeanexchangerates.exchangeapi.util.DataDownloader;
+import com.europeanexchangerates.exchangeapi.provider.UrlCsvZipExchangeRateProvider;
 import com.europeanexchangerates.exchangeapi.util.NullableConverter;
 
 @SpringBootTest
@@ -35,7 +35,7 @@ public class ExchangeRateServiceTest {
     private ExchangeRateService exchangeRateService;
 
     @Mock
-    DataDownloader dataDownloader;
+    UrlCsvZipExchangeRateProvider exchangeRateProvider;
 
     @BeforeEach
     void setUp() throws Exception {
@@ -82,9 +82,9 @@ void setUp() throws Exception {
                 }));
             }
         };
-        when(dataDownloader.downloadData()).thenReturn(dummyData);
+        when(exchangeRateProvider.getExchangeRates()).thenReturn(dummyData);
 
-        exchangeRateService = new ExchangeRateService(dataDownloader);
+        exchangeRateService = new ExchangeRateService(exchangeRateProvider);
     }
 
     @ParameterizedTest