Re: why in permission ,can't do like this?

Peter Duniho wrote:


One more verbose way to handle the illegal argument check is with a specific
separate null value check. Though it's verbose, it is nicely
self-documenting. Whether you want to treat null as an out-of-band illegal
value like this depends on the semantics of your application model. It's
perfectly legitimate otherwise to treat null as just another illegal value.

  if ( name == null )
  {
    throw new IllegalArgumentException(
          new NullPointerException( "null name" ));
  }
  if ( name.equals( "getInstance" ))
  {
    doNameInstanceThing();
  }
  else if ( name.equals( "setUtil" ))
  {
    doSetUtilThing();
  }
  else
  {
    throw new IllegalArgumentException( "bad name: "+ name );
  }

Then I look at that and want doWhatever() methods to be the implementors of a
PermissionHandler interface, selected from a Map based on the passed 'name'
String. Getting null for a Handler from the Map means an illegal argument.

  Class <? extends PermissionHandler> clazz = handlers.get( name );
  if ( clazz == null )
  {
    throw new IllegalArgumentException( "bad name: "+ name );
  }
  PermissionHandler handler = clazz.newInstance();
  handler.doWhatever( name );

(error checks omitted)

Then the String 'name' argument can come from, say, a deployment descriptor or
properties file, as can the 'handlers' elements. It makes perfect sense for
code to accept client-driven parameters if it's a framework setup like that.
The clients in this case are disciplined classes working off well-documented
setup files, so they are relatively trustworthy. Of course, the accepting
class must produce meaningful log messages for the operations folks in case
there is a mistake.

--
Lew