Support 'empty' StreamSource in Jaxb2Marshaller

Added support for StreamSources that do not have a InputStream or
Reader, but do have a System ID.

Issue: 10828

spring-oxm/src/main/java/org/springframework/oxm/jaxb/Jaxb2Marshaller.java

@@ -784,6 +784,9 @@ public class Jaxb2Marshaller implements MimeMarshaller, MimeUnmarshaller, Generi
 			else if (streamSource.getReader() != null) {
 				inputSource = new InputSource(streamSource.getReader());
 			}
+			else {
+				inputSource = new InputSource(streamSource.getSystemId());
+			}
 		}
 
 		try {

spring-oxm/src/test/java/org/springframework/oxm/jaxb/Jaxb2UnmarshallerTests.java

@@ -16,8 +16,9 @@
 
 package org.springframework.oxm.jaxb;
 
+import java.io.File;
+import java.io.IOException;
 import java.io.StringReader;
-
 import javax.activation.DataHandler;
 import javax.activation.FileDataSource;
 import javax.xml.bind.JAXBElement;
@@ -26,7 +27,11 @@ import javax.xml.stream.XMLStreamReader;
 import javax.xml.transform.Source;
 import javax.xml.transform.stream.StreamSource;
 
+import static org.junit.Assert.*;
 import org.junit.Test;
+import static org.mockito.BDDMockito.given;
+import static org.mockito.BDDMockito.mock;
+
 import org.springframework.core.io.ClassPathResource;
 import org.springframework.core.io.Resource;
 import org.springframework.oxm.AbstractUnmarshallerTests;
@@ -36,9 +41,6 @@ import org.springframework.oxm.jaxb.test.Flights;
 import org.springframework.oxm.mime.MimeContainer;
 import org.springframework.util.xml.StaxUtils;
 
-import static org.junit.Assert.*;
-import static org.mockito.BDDMockito.*;
-
 /**
  * @author Arjen Poutsma
  * @author Biju Kunjummen
@@ -134,4 +136,13 @@ public class Jaxb2UnmarshallerTests extends AbstractUnmarshallerTests {
 				"test", airplane.getValue().getName());
 	}
 
+	@Test
+	public void unmarshalFile() throws IOException {
+		Resource resource = new ClassPathResource("jaxb2.xml", getClass());
+		File file = resource.getFile();
+
+		Flights f = (Flights) unmarshaller.unmarshal(new StreamSource(file));
+		testFlights(f);
+	}
+
 }

spring-oxm/src/test/resources/org/springframework/oxm/jaxb/jaxb2.xml

@@ -0,0 +1,5 @@
+<tns:flights xmlns:tns="http://samples.springframework.org/flight">
+    <tns:flight>
+        <tns:number>42</tns:number>
+    </tns:flight>
+</tns:flights>