1 /* 2 * Copyright (c) 1999, 2011, Oracle and/or its affiliates. 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. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * 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 // List<NamedWeakReference<Class | Object>> 41 private List<NamedWeakReference<Object>> factories; 42 private int posn = 0; 43 private ClassLoader loader; 44 45 /** 46 * Records the input list and uses it directly to satisfy 47 * hasMore()/next() requests. An alternative would have been to use 48 * an enumeration/iterator from the list, but we want to update the 49 * list so we keep the 50 * original list. The list initially contains Class objects. 51 * As each element is used, the Class object is replaced by an 52 * instance of the Class itself; eventually, the list contains 53 * only a list of factory instances and no more updates are required. 54 * 55 * <p> Both Class objects and factories are wrapped in weak 56 * references so as not to prevent GC of the class loader. Each 57 * weak reference is tagged with the factory's class name so the 58 * class can be reloaded if the reference is cleared. 59 * 60 * @param factories A non-null list 61 * @param loader The class loader of the list's contents 62 * 63 * This internal method is used with Thread Context Class Loader (TCCL), 64 * please don't expose this method as public. 65 */ 66 FactoryEnumeration(List<NamedWeakReference<Object>> factories, 67 ClassLoader loader) { 68 this.factories = factories; 69 this.loader = loader; 70 } 71 72 public Object next() throws NamingException { 73 synchronized (factories) { 74 75 NamedWeakReference<Object> ref = factories.get(posn++); 76 Object answer = ref.get(); 77 if ((answer != null) && !(answer instanceof Class)) { 78 return answer; 79 } 80 81 String className = ref.getName(); 82 83 try { 84 if (answer == null) { // reload class if weak ref cleared 85 Class<?> cls = Class.forName(className, true, loader); 86 answer = cls; 87 } 88 // Instantiate Class to get factory 89 answer = ((Class) answer).newInstance(); 90 ref = new NamedWeakReference<>(answer, className); 91 factories.set(posn-1, ref); // replace Class object or null 92 return answer; 93 } catch (ClassNotFoundException e) { 94 NamingException ne = 95 new NamingException("No longer able to load " + className); 96 ne.setRootCause(e); 97 throw ne; 98 } catch (InstantiationException e) { 99 NamingException ne = 100 new NamingException("Cannot instantiate " + answer); 101 ne.setRootCause(e); 102 throw ne; 103 } catch (IllegalAccessException e) { 104 NamingException ne = new NamingException("Cannot access " + answer); 105 ne.setRootCause(e); 106 throw ne; 107 } 108 } 109 } 110 111 public boolean hasMore() { 112 synchronized (factories) { 113 return posn < factories.size(); 114 } 115 } 116 }