117 lines
4.5 KiB
Java
117 lines
4.5 KiB
Java
/*
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* Copyright (c) 1999, 2011, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package com.sun.naming.internal;
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import java.util.List;
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import javax.naming.NamingException;
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/**
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* The FactoryEnumeration is used for returning factory instances.
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*
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* @author Rosanna Lee
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* @author Scott Seligman
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*/
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// no need to implement Enumeration since this is only for internal use
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public final class FactoryEnumeration {
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// List<NamedWeakReference<Class | Object>>
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private List<NamedWeakReference<Object>> factories;
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private int posn = 0;
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private ClassLoader loader;
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/**
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* Records the input list and uses it directly to satisfy
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* hasMore()/next() requests. An alternative would have been to use
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* an enumeration/iterator from the list, but we want to update the
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* list so we keep the
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* original list. The list initially contains Class objects.
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* As each element is used, the Class object is replaced by an
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* instance of the Class itself; eventually, the list contains
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* only a list of factory instances and no more updates are required.
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*
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* <p> Both Class objects and factories are wrapped in weak
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* references so as not to prevent GC of the class loader. Each
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* weak reference is tagged with the factory's class name so the
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* class can be reloaded if the reference is cleared.
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*
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* @param factories A non-null list
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* @param loader The class loader of the list's contents
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*
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* This internal method is used with Thread Context Class Loader (TCCL),
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* please don't expose this method as public.
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*/
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FactoryEnumeration(List<NamedWeakReference<Object>> factories,
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ClassLoader loader) {
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this.factories = factories;
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this.loader = loader;
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}
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public Object next() throws NamingException {
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synchronized (factories) {
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NamedWeakReference<Object> ref = factories.get(posn++);
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Object answer = ref.get();
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if ((answer != null) && !(answer instanceof Class)) {
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return answer;
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}
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String className = ref.getName();
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try {
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if (answer == null) { // reload class if weak ref cleared
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Class<?> cls = Class.forName(className, true, loader);
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answer = cls;
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}
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// Instantiate Class to get factory
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answer = ((Class) answer).newInstance();
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ref = new NamedWeakReference<>(answer, className);
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factories.set(posn-1, ref); // replace Class object or null
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return answer;
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} catch (ClassNotFoundException e) {
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NamingException ne =
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new NamingException("No longer able to load " + className);
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ne.setRootCause(e);
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throw ne;
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} catch (InstantiationException e) {
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NamingException ne =
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new NamingException("Cannot instantiate " + answer);
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ne.setRootCause(e);
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throw ne;
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} catch (IllegalAccessException e) {
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NamingException ne = new NamingException("Cannot access " + answer);
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ne.setRootCause(e);
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throw ne;
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}
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}
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}
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public boolean hasMore() {
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synchronized (factories) {
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return posn < factories.size();
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}
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}
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}
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