Fix an issue with JsonLDConverter. Add test

src/main/java/com/ontotext/kafka/convert/JsonDataConverter.java

@@ -4,9 +4,11 @@
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.DatabindException;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import org.apache.commons.collections4.CollectionUtils;
 import org.eclipse.rdf4j.rio.RDFFormat;
 
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.Map;
 
 public final class JsonDataConverter extends RdfFormatConverter {
@@ -18,6 +20,7 @@ public JsonDataConverter(RDFFormat inputFormat) {
 		this.objectMapper = new ObjectMapper();
 	}
 
+
 	public <T> T convert(byte[] data, Class<T> cls) {
 		try {
 			byte[] converted = convertData(data);
@@ -33,12 +36,23 @@ public <T> T convert(byte[] data, Class<T> cls) {
 	}
 
 	public Map<String, Object> convert(byte[] data) {
+		byte[] converted = null;
 		try {
-			byte[] converted = convertData(data);
-			return objectMapper.readValue(converted, new TypeReference<>() {
+			converted = convertData(data);
+			ArrayList<Map<String, Object>> res = objectMapper.readValue(converted, new TypeReference<>() {
 			});
+			if (CollectionUtils.isNotEmpty(res)) {
+				return res.get(0);
+			}
 		} catch (DatabindException e) {
-			log.error("Could not deserialize data to a generic map", e);
+			// Just in case try to deserialize straight to a map without the outer list wrapper.
+			log.error("Could not deserialize data to a list of items. Will repeat and try to deserialize as a map instead.");
+			try {
+				return objectMapper.readValue(converted, new TypeReference<>() {
+				});
+			} catch (Exception e1) {
+				log.error("Could not deserialize data to a map. Cannot proceed", e);
+			}
 		} catch (StreamReadException e) {
 			log.error("Caught exception while reading data stream", e);
 		} catch (IOException e) {

src/test/java/com/ontotext/kafka/convert/JsonDataConverterTest.java

@@ -0,0 +1,24 @@
+package com.ontotext.kafka.convert;
+
+import org.eclipse.rdf4j.rio.RDFFormat;
+import org.junit.jupiter.api.Test;
+
+import java.nio.charset.StandardCharsets;
+import java.util.Collections;
+import java.util.Map;
+
+import static org.assertj.core.api.AssertionsForInterfaceTypes.assertThat;
+
+class JsonDataConverterTest {
+
+
+	@Test
+	void test_convertToMap_ok() {
+		String ttl = "<urn:a> <urn:b> <urn:c> .";
+		JsonDataConverter converter = new JsonDataConverter(RDFFormat.TURTLE);
+		Map<String, Object> data = converter.convert(ttl.getBytes(StandardCharsets.UTF_8));
+		assertThat(data).isNotNull();
+		assertThat(data).containsEntry("@id", "urn:a");
+		assertThat(data).containsEntry("urn:b", Collections.singletonList(Collections.singletonMap("@id", "urn:c")));
+	}
+}