jaxp validation ref WeakReference xni grammars XMLGrammarPool weakreferencexmlschema abstractxmlschema weakreference fgrammarpool weakreference weakreferencexmlschema xmlgrammarpool getgrammarpool xmlgrammarpool grammarpool xmlgrammarpool fgrammarpool.get grammarpool grammarpool softreferencegrammarpool fgrammarpool weakreference grammarpool grammarpool isfullycomposed