FileDocCategorySizeDatePackage
FactoryEnumeration.javaAPI DocJava SE 5 API2897Fri Aug 26 14:55:16 BST 2005com.sun.naming.internal

FactoryEnumeration

public final class FactoryEnumeration extends Object
The FactoryEnumeration is used for returning factory instances.
author
Rosanna Lee
author
Scott Seligman
version
1.8 03/12/19

Fields Summary
private List
factories
private int
posn
private ClassLoader
loader
Constructors Summary
FactoryEnumeration(List factories, ClassLoader loader)
Records the input list and uses it directly to satisfy hasMore()/next() requests. An alternative would have been to use an enumeration/iterator from the list, but we want to update the list so we keep the original list. The list initially contains Class objects. As each element is used, the Class object is replaced by an instance of the Class itself; eventually, the list contains only a list of factory instances and no more updates are required.

Both Class objects and factories are wrapped in weak references so as not to prevent GC of the class loader. Each weak reference is tagged with the factory's class name so the class can be reloaded if the reference is cleared.

param
factories A non-null list
param
loader The class loader of the list's contents


                                                                                                                              	    	           
        
	this.factories = factories;
	this.loader = loader;
Methods Summary
public booleanhasMore()

	synchronized (factories) {
	    return posn < factories.size();
	}
public java.lang.Objectnext()

	synchronized (factories) {

	    NamedWeakReference ref = (NamedWeakReference) factories.get(posn++);
	    Object answer = ref.get();
	    if ((answer != null) && !(answer instanceof Class)) {
		return answer;
	    }

	    String className = ref.getName();

	    try {
		if (answer == null) {	// reload class if weak ref cleared
		    answer = Class.forName(className, true, loader);
		}
		// Instantiate Class to get factory
		answer = ((Class) answer).newInstance();
		ref = new NamedWeakReference(answer, className);
		factories.set(posn-1, ref);  // replace Class object or null
		return answer;
	    } catch (ClassNotFoundException e) {
		NamingException ne = 
		    new NamingException("No longer able to load " + className);
		ne.setRootCause(e);
		throw ne;
	    } catch (InstantiationException e) {
		NamingException ne = 
		    new NamingException("Cannot instantiate " + answer);
		ne.setRootCause(e);
		throw ne;
	    } catch (IllegalAccessException e) {
		NamingException ne = new NamingException("Cannot access " + answer);
		ne.setRootCause(e);
		throw ne;
	    }
	}