[jboss-dev-forums] [Design the new POJO MicroContainer] - Re: MC tools

[alesj]

"flavia.rainone at jboss.com" wrote : 
  | But, of course, I can't change the meta data classes, adding a method that generates the XML form of each one of them. So, how can I get rid of my if instanceof statements and still generate proper XML for every meta data type?
  | 
  | I guess I missed what you're trying to tell me. So, please, elaborate :)
I don't know the name of the pattern, but it's trivial to do it. ;-)
Instead of changing the classes, you can write proper adapters / delegates.

e.g. (pseudo code)

  | // T --> SMD side metadata type; e.g. ServiceInjectionValueMetaData
  | // U --> BMD side metadata type; e.g. AbstractInjectionValueMetaData
  | interface SMD2BMD<T, U>
  | {
  |    Class<T> mappingClass();
  | 
  |    U toBMD(T t);
  | 
  |    String toXML(U u);
  | }
  | 

Where now instead of multiple ifs, you would simply do something like this:

  | Map<?, ?> adapters = ...;
  | SMD2BMD s2b = adapters.get(smd.getClass());
  | if (s2b == null)
  | {
  |    // no exact mapping class match, lets iterate
  |   for (Class key : adapters.keySet())
  |   {
  |       if (key.isInstance(smd))
  |       {
  |          s2b = adapters.get(key);
  |          break;
  |       }
  |    }
  |    if (s2b == null)
  |       throw new IllegalArgumentException("No such mapping " + smd);
  | }
  | 

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