MODOAIPMH-556 - Improve clarity of the error message (folio-org#377)

src/main/java/org/folio/oaipmh/ResponseConverter.java

@@ -10,10 +10,12 @@
 import org.openarchives.oai._2_0.oai_identifier.OaiIdentifier;
 import org.purl.dc.elements._1.ObjectFactory;
 import org.xml.sax.SAXException;
+import org.xml.sax.SAXParseException;
 
 import javax.xml.bind.JAXBContext;
 import javax.xml.bind.JAXBException;
 import javax.xml.bind.Marshaller;
+import javax.xml.bind.UnmarshalException;
 import javax.xml.bind.Unmarshaller;
 import javax.xml.transform.stream.StreamSource;
 import javax.xml.validation.Schema;
@@ -160,14 +162,20 @@ public Object bytesToObject(byte[] byteSource) {
         jaxbUnmarshaller.setSchema(oaipmhSchema);
       }
       return jaxbUnmarshaller.unmarshal(inputStream);
-    } catch (JAXBException | IOException e) {
+    }  catch (JAXBException | IOException e) {
       // In case there is an issue to unmarshal byteSource, there is no way to handle it
-      throw new IllegalStateException("The byte array cannot be converted to JAXB object response.", e);
+      throw new IllegalStateException(processException(e), e);
     } finally {
       logExecutionTime("Array of bytes converted to Object", timer);
     }
   }
 
+  private String processException(Exception e) {
+    return e instanceof UnmarshalException ue && ue.getLinkedException() instanceof SAXParseException se ?
+      se.getLocalizedMessage() :
+      "The byte array cannot be converted to JAXB object response.";
+  }
+
   /**
    * @return Checks if the Jaxb context initialized successfully
    */

src/test/java/org/folio/oaipmh/ResponseConverterTest.java

@@ -11,11 +11,13 @@
 import javax.xml.bind.JAXBException;
 import java.time.Instant;
 
+import static org.hamcrest.CoreMatchers.containsString;
 import static org.hamcrest.CoreMatchers.instanceOf;
 import static org.hamcrest.CoreMatchers.not;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.core.IsEqual.equalTo;
 import static org.hamcrest.text.IsEmptyString.isEmptyOrNullString;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.fail;
 
 
@@ -67,4 +69,12 @@ void successCase() {
 
     assertThat(oaipmh, equalTo(oaipmhFromString));
   }
+
+  @Test
+  void shouldProvideDetailedErrorMessage() {
+    var source = "<?xml version=\"1.0\" encoding=\"UTF-8\"?><marc:record xmlns:marc=\"http://www.loc.gov/MARC21/slim\"><marc:leader>01344nja a2200289 c 4500</marc:leader><marc:datafield tag=\"035\" ind1=\" \" ind2=\" \"><marc:subfield code=\"a\">(DE-599)GBV\u001f1011162431</marc:subfield></marc:record>\n".getBytes();
+    var converter = ResponseConverter.getInstance();
+    var exception = assertThrows(IllegalStateException.class, () -> converter.bytesToObject(source));
+    assertThat(exception.getMessage(), containsString("An invalid XML character (Unicode: 0x1f) was found in the element content of the document."));
+  }
 }