Handle dcat:DataServices correctly

Check that dcat:DataServices as preserved.
Do not add a dcat:downloadURL to a dcat:Distribution that is served by a DataService.

src/main/java/de/landsh/opendata/catalogproxy/CatalogFilter.java

@@ -130,8 +130,9 @@ public class CatalogFilter implements InitializingBean {
 
             final Resource accessURL = distribution.getPropertyResourceValue(DCAT.accessURL);
             final Resource downloadURL = distribution.getPropertyResourceValue(DCAT.downloadURL);
+            final boolean hasAccessService = distribution.hasProperty(DCAT.accessService);
 
-            if (downloadURL == null) {
+            if (downloadURL == null && !hasAccessService) {
                 distribution.addProperty(DCAT.downloadURL, accessURL);
             }
         }

src/test/java/de/landsh/opendata/catalogproxy/CatalogFilterTest.java

@@ -277,4 +277,49 @@ public class CatalogFilterTest {
             assertTrue(model.listStatements(null, DCAT.startDate, (String) null).hasNext());
         }
     }
+
+    /**
+     * A data service must be preserved.
+     */
+    @Test
+    public void dataservice() throws IOException {
+        try (final InputStream inputStream = getClass().getResourceAsStream("/dataservice.xml")) {
+            final Model model = catalogFilter.work(inputStream);
+
+            assertEquals(1, model.listStatements(null, RDF.type, DCAT.Dataset).toList().size(), "one dcat:Dataset");
+            assertEquals(4, model.listStatements(null, RDF.type, DCAT.Distribution).toList().size(), "four dcat:Distribution");
+            assertEquals(2, model.listStatements(null, RDF.type, DCAT.DataService).toList().size(), "two dcat:DataService");
+        }
+    }
+
+    /**
+     * In case of a dcat:DataService no dcat:downloadURL must be added to a dcat:Distribution
+     * <a href="https://www.dcat-ap.de/def/dcatde/2.0/implRules/#konvention-41">Konvention 41</a> states that a
+     * dcat:Distribution MUST NOT have a dcat:downloadURL property.
+     */
+    @Test
+    public void addDownloadURLs_DataService() {
+        final Model model = parseRdf(getClass().getResourceAsStream("/dataservice.xml"));
+
+        catalogFilter.addDownloadURLs(model);
+
+        Resource distributionWithService1 = model.getResource("https://umweltgeodienste.schleswig-holstein.de/WMS_UWAT_NAT?");
+        Resource distributionWithService2 = model.getResource("https://umweltgeodienste.schleswig-holstein.de/WFS_UWAT?");
+        Resource distributionWithoutService1 = model.getResource("https://umweltgeodienste.schleswig-holstein.de/WFS_UWAT?service=wfs&version=2.0.0&request=GetFeature&typeNames=app:ramsar");
+        Resource distributionWithoutService2 = model.getResource("https://opendata.schleswig-holstein.de/data/llur55/ramsar_utm32.zip");
+
+        assertTrue(distributionWithService1.hasProperty(DCAT.accessURL));
+        assertTrue(distributionWithService1.hasProperty(DCAT.accessService));
+        assertFalse(distributionWithService1.hasProperty(DCAT.downloadURL), "a dcat:Distribution with a dcat:DataService MUST NOT have a dcat:downloadURL");
+
+        assertTrue(distributionWithService2.hasProperty(DCAT.accessURL));
+        assertTrue(distributionWithService2.hasProperty(DCAT.accessService));
+        assertFalse(distributionWithService2.hasProperty(DCAT.downloadURL), "a dcat:Distribution with a dcat:DataService MUST NOT have a dcat:downloadURL");
+
+        assertTrue(distributionWithoutService1.hasProperty(DCAT.accessURL));
+        assertTrue(distributionWithoutService1.hasProperty(DCAT.downloadURL));
+        
+        assertTrue(distributionWithoutService2.hasProperty(DCAT.accessURL));
+        assertTrue(distributionWithoutService2.hasProperty(DCAT.downloadURL));
+    }
 }