code adapted as per Michele's recommendations

dhp-workflows/dhp-aggregation/src/main/java/eu/dnetlib/dhp/transformation/xslt/DataFetcher.java

@@ -1,4 +1,8 @@
 package eu.dnetlib.dhp.transformation.xslt;
+
+import java.io.Serializable;
+import net.sf.saxon.s9api.*;
+
 import org.apache.commons.io.IOUtils;
 import org.json.JSONObject;
 import java.io.IOException;
@@ -11,12 +15,8 @@ import java.util.List;
  * a Dublin Core. This functionality is particularly needed for OSF Preprints
  */
 
-/**
- * this method fetches JSON from a provided URL and returns it as JSON Object
- */
 
-
-public class DataFetcher {
+public class DataFetcher implements ExtensionFunction, Serializable {
 
     /**
      * this method fetches JSON from a provided URL and returns it as Dublin Core
@@ -30,7 +30,7 @@ public class DataFetcher {
 
     /**
      * This method fetches JSON object from a given URL
-     * @param url
+     * @param url a url in the metadata for fetching authors in JSON format
      * @return
      * @throws IOException
      */
@@ -87,4 +87,32 @@ public class DataFetcher {
         }
         return dublinCoreAuthors;
     }
+
+    /**
+     * todo: add documentation
+     */
+    public static String getAndTransformAuthors(URL url) throws IOException{
+        return String.join(", ", transformListToDublinCore(getAuthorsFromJson(getJson(url))));
+    }
+
+
+    @Override
+    public QName getName() {
+        return null;
+    }
+
+    @Override
+    public SequenceType getResultType() {
+        return null;
+    }
+
+    @Override
+    public SequenceType[] getArgumentTypes() {
+        return new SequenceType[0];
+    }
+
+    @Override
+    public XdmValue call(XdmValue[] xdmValues) throws SaxonApiException {
+        return null;
+    }
 }

dhp-workflows/dhp-aggregation/src/main/java/eu/dnetlib/dhp/transformation/xslt/XSLTTransformationFunction.java

@@ -55,6 +55,8 @@ public class XSLTTransformationFunction implements MapFunction<MetadataRecord, M
 		processor.registerExtensionFunction(new DateCleaner());
 		processor.registerExtensionFunction(new PersonCleaner());
 
+		processor.registerExtensionFunction(new DataFetcher());
+
 		final XsltCompiler comp = processor.newXsltCompiler();
 		QName datasourceIDParam = new QName(DATASOURCE_ID_PARAM);
 		comp.setParameter(datasourceIDParam, new XdmAtomicValue(value.getProvenance().getDatasourceId()));

dhp-workflows/dhp-aggregation/src/test/java/eu/dnetlib/dhp/transformation/xslt/DataFetcherTest.java

@@ -38,7 +38,7 @@ class DataFetcherTest {
                 .getString("full_name");
         System.out.println(x);
         System.out.println(testJsonObj.getJSONArray("data").length());
-        testJsonObj.getJSONArray("data").forEach(json1 -> System.out.println(json1));
+        testJsonObj.getJSONArray("data").forEach(System.out::println);
     }
 
     @Test
@@ -48,6 +48,13 @@ class DataFetcherTest {
         List<String> authors = DataFetcher.getAuthorsFromJson(testJsonObj);
         System.out.println(authors);
         System.out.println(DataFetcher.transformListToDublinCore(authors));
-
     }
+
+    @Test
+    void getAndTransformAuthors() throws IOException, URISyntaxException {
+        URL contributorsUrl = new URI("https://api.osf.io/v2/preprints/mrwqb/contributors/?format=json").toURL();
+        System.out.println(DataFetcher.getAndTransformAuthors(contributorsUrl));
+    }
+
+
 }