MetadataCacheAttributeSource's HashMap must be synchronized

MetadataCacheAttributeSource uses a HashMap to cache attributes for the method of the target object. The HashMap is not thread safe. In realy multi threaded environment, such as a heavily stressed tomcat running on a multi-cpu system, this leads to corruption of the HashMap buckets internal structure with disastrous results (infinite loop in get() ).

Fixable using a call to Collections.synchronizedMap() at attribute HashMap creation.