title: classes qualify to be spring beans
body: <p>In big enterprise projects which objects qualify to use as a spring bean and which are not ?
  The types of classes I can think of are requests, responses, services. helpers, registries, business objects, factories, validation rules, adapters and many more as per app requirements.</p>
  
  <p>Can all of them can be springified ? </p>
  
  <p>If everything is injected then what is the use of pure singletons ? Does static invocations has no use ? </p>