J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 1999-2001 Sun Microsystems, Inc. All Rights Reserved. |
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| 4 | * |
| 5 | * This code is free software; you can redistribute it and/or modify it |
| 6 | * under the terms of the GNU General Public License version 2 only, as |
| 7 | * published by the Free Software Foundation. Sun designates this |
| 8 | * particular file as subject to the "Classpath" exception as provided |
| 9 | * by Sun in the LICENSE file that accompanied this code. |
| 10 | * |
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT |
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| 14 | * version 2 for more details (a copy is included in the LICENSE file that |
| 15 | * accompanied this code). |
| 16 | * |
| 17 | * You should have received a copy of the GNU General Public License version |
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, |
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| 20 | * |
| 21 | * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 22 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 23 | * have any questions. |
| 24 | */ |
| 25 | |
| 26 | package com.sun.naming.internal; |
| 27 | |
| 28 | import java.util.List; |
| 29 | import javax.naming.NamingException; |
| 30 | |
| 31 | /** |
| 32 | * The FactoryEnumeration is used for returning factory instances. |
| 33 | * |
| 34 | * @author Rosanna Lee |
| 35 | * @author Scott Seligman |
| 36 | */ |
| 37 | |
| 38 | // no need to implement Enumeration since this is only for internal use |
| 39 | public final class FactoryEnumeration { |
| 40 | private List factories; |
| 41 | private int posn = 0; |
| 42 | private ClassLoader loader; |
| 43 | |
| 44 | /** |
| 45 | * Records the input list and uses it directly to satisfy |
| 46 | * hasMore()/next() requests. An alternative would have been to use |
| 47 | * an enumeration/iterator from the list, but we want to update the |
| 48 | * list so we keep the |
| 49 | * original list. The list initially contains Class objects. |
| 50 | * As each element is used, the Class object is replaced by an |
| 51 | * instance of the Class itself; eventually, the list contains |
| 52 | * only a list of factory instances and no more updates are required. |
| 53 | * |
| 54 | * <p> Both Class objects and factories are wrapped in weak |
| 55 | * references so as not to prevent GC of the class loader. Each |
| 56 | * weak reference is tagged with the factory's class name so the |
| 57 | * class can be reloaded if the reference is cleared. |
| 58 | |
| 59 | * @param factories A non-null list |
| 60 | * @param loader The class loader of the list's contents |
| 61 | */ |
| 62 | FactoryEnumeration(List factories, ClassLoader loader) { |
| 63 | this.factories = factories; |
| 64 | this.loader = loader; |
| 65 | } |
| 66 | |
| 67 | public Object next() throws NamingException { |
| 68 | synchronized (factories) { |
| 69 | |
| 70 | NamedWeakReference ref = (NamedWeakReference) factories.get(posn++); |
| 71 | Object answer = ref.get(); |
| 72 | if ((answer != null) && !(answer instanceof Class)) { |
| 73 | return answer; |
| 74 | } |
| 75 | |
| 76 | String className = ref.getName(); |
| 77 | |
| 78 | try { |
| 79 | if (answer == null) { // reload class if weak ref cleared |
| 80 | answer = Class.forName(className, true, loader); |
| 81 | } |
| 82 | // Instantiate Class to get factory |
| 83 | answer = ((Class) answer).newInstance(); |
| 84 | ref = new NamedWeakReference(answer, className); |
| 85 | factories.set(posn-1, ref); // replace Class object or null |
| 86 | return answer; |
| 87 | } catch (ClassNotFoundException e) { |
| 88 | NamingException ne = |
| 89 | new NamingException("No longer able to load " + className); |
| 90 | ne.setRootCause(e); |
| 91 | throw ne; |
| 92 | } catch (InstantiationException e) { |
| 93 | NamingException ne = |
| 94 | new NamingException("Cannot instantiate " + answer); |
| 95 | ne.setRootCause(e); |
| 96 | throw ne; |
| 97 | } catch (IllegalAccessException e) { |
| 98 | NamingException ne = new NamingException("Cannot access " + answer); |
| 99 | ne.setRootCause(e); |
| 100 | throw ne; |
| 101 | } |
| 102 | } |
| 103 | } |
| 104 | |
| 105 | public boolean hasMore() { |
| 106 | synchronized (factories) { |
| 107 | return posn < factories.size(); |
| 108 | } |
| 109 | } |
| 110 | } |