clarify stax comments, change logging level

git-svn-id: https://svn.apache.org/repos/asf/lucene/solr/trunk@577432 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/solr/handler/XmlUpdateRequestHandler.java

@@ -83,12 +83,18 @@ public class XmlUpdateRequestHandler extends RequestHandlerBase
     
     inputFactory = BaseXMLInputFactory.newInstance();
     try {
+      // The java 1.6 bundled stax parser (sjsxp) does not currently have a thread-safe
+      // XMLInputFactory, as that implementation tries to cache and reuse the
+      // XMLStreamReader.  Setting the parser-specific "reuse-instance" property to false
+      // prevents this.
+      // All other known open-source stax parsers (and the bea ref impl)
+      // have thread-safe factories.
       inputFactory.setProperty("reuse-instance", Boolean.FALSE);
     }
     catch( IllegalArgumentException ex ) {
-      // The java 1.5 com.bea.xml does not support this property, but behaves properly in a
-      // multi-threaded environment.  Ignore the error for 1.5
-      log.info( "Unable to set the 'reuse-instance' property for the input factory: "+inputFactory );
+      // Other implementations will likely throw this exception since "reuse-instance"
+      // isimplementation specific.
+      log.fine( "Unable to set the 'reuse-instance' property for the input factory: "+inputFactory );
     }
   }