synchronized validation to avoid concurrency issues like FWK005

Author: nemonik

src/main/java/org/mitre/stix/STIXSchema.java

@@ -256,8 +256,12 @@ public boolean validate(String xmlText) throws SAXException {
 		}
 
 		try {
-			validator.validate(new StreamSource(new ByteArrayInputStream(
-					xmlText.getBytes(StandardCharsets.UTF_8))));
+			// synchronized to avoid org.xml.sax.SAXException: FWK005 parse may
+			// not be called while parsing.
+			synchronized (this) {
+				validator.validate(new StreamSource(new ByteArrayInputStream(
+						xmlText.getBytes(StandardCharsets.UTF_8))));
+			}
 		} catch (IOException e) {
 			throw new RuntimeException(e);
 		} catch (SAXException e) {