Fail PDF generation early on objects with unsupported format

git-svn-id: https://develop.sub.uni-goettingen.de/repos/textgrid/trunk/services/aggregator@13728 7c539038-3410-0410-b1ec-0f2a7bf1c452

src/main/java/info/textgrid/services/aggregator/pdf/PDF.java

@@ -77,11 +77,16 @@ public Response get(@PathParam("uri") final URI uri,
 					mapping, true);
 			rewriter.configure(URI.create("internal:tei#tei"));
 			rewriter.recordMissingReferences();
+			final TGOSupplier<InputStream> textSupplier = repository.read(uri, sid);
+			final String rootObjectFormat = textSupplier.getMetadata().getGeneric().getProvided().getFormat();
+			if (!rootObjectFormat.startsWith("text/xml"))
+				return GenericExceptionMapper.toResponse(Status.UNSUPPORTED_MEDIA_TYPE, "PDF generation currently supports only text/xml documents. The requested document, " + uri + ", has an invalid document type, however:", rootObjectFormat);
+
 			final FileBackedOutputStream buffer = new FileBackedOutputStream(
 					1024 * 1024);
-			final TGOSupplier<InputStream> textSupplier = repository.read(uri, sid);
 			rewriter.rewrite(textSupplier.getInput(), buffer);
 
+
 			// now download the missing references if applicable, add
 			// them to the mapping
 			final Set<String> linkedURIs = rewriter.getMissingReferences();