1 <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN"> 2 <HTML> 3 <HEAD> 4 <!-- 5 6 Copyright (c) 2001, Oracle and/or its affiliates. All rights reserved. 7 DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 8 9 This code is free software; you can redistribute it and/or modify it 10 under the terms of the GNU General Public License version 2 only, as 11 published by the Free Software Foundation. Oracle designates this 12 particular file as subject to the "Classpath" exception as provided 13 by Oracle in the LICENSE file that accompanied this code. 14 15 This code is distributed in the hope that it will be useful, but WITHOUT 16 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 17 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 18 version 2 for more details (a copy is included in the LICENSE file that 19 accompanied this code). 20 21 You should have received a copy of the GNU General Public License version 22 2 along with this work; if not, write to the Free Software Foundation, 23 Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 24 25 Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 26 or visit www.oracle.com if you need additional information or have any 27 questions. 28 29 --> 30 </HEAD> 31 <BODY BGCOLOR="white"> 32 <P> 33 34 <B> Licensee impact of JDK 1.4 reflection changes </B> 35 36 </P> 37 <P> 38 39 Sun's JDK 1.4 contains a new implementation of java.lang.reflect which 40 offers substantially higher performance than previous JDKs' native 41 code. Licensees can at their discretion port these changes. There are 42 no public API or documentation changes associated with the new 43 reflection implementation aside from a few minor clarifications in the 44 specifications of Method.invoke(), Constructor.newInstance(), and a 45 few methods in java.lang.reflect.Field. 46 47 </P> 48 <P> 49 50 The bulk of the new implementation is Java programming language code 51 which generates bytecodes, and is therefore portable. If licensees 52 desire to port it, the following JVM changes are required: 53 54 <OL> 55 <LI> The following four new JVM entry points must be added: 56 57 <UL> 58 <LI> JVM_GetClassDeclaredConstructors 59 <LI> JVM_GetClassDeclaredFields 60 <LI> JVM_GetClassDeclaredMethods 61 <LI> JVM_GetClassAccessFlags 62 </UL> 63 64 The first three return the declared constructors, fields, and methods 65 for a given class, with an option to return only the public ones. They 66 are similar in functionality to the earlier GetClassConstructors, 67 GetClassFields, and GetClassMethods. JVM_GetClassDeclaredFields and 68 JVM_GetClassDeclaredMethods must intern the Strings for the names of 69 the Field and Method objects returned. The fouth returns the access 70 flags for a given class as marked in the class file, as opposed to in 71 the InnerClasses attribute if the class is an inner class, and 72 therefore differs from JVM_GetClassModifiers for inner classes (most 73 importantly, protected inner classes; see 4471811.) 74 75 <LI> The JVM's link resolver must be modified to allow all field and 76 method references from subclasses of sun.reflect.MagicAccessorImpl to 77 any other class (even to private members of other classes) to 78 succeed. This allows setAccessible() and its associated checks to be 79 implemented in Java. 80 81 <LI> The code which calls the verifier must skip verification for all 82 subclasses of sun.reflect.MagicAccessorImpl. (It was originally 83 intended that only a subset of the stub classes used for serialization 84 would not pass the verifier, specifically, those subclassing 85 SerializationConstructorAccessorImpl; see 4486457 for a case where 86 this does not work.) 87 88 <LI> The stack walker for security checks must be modified to skip not 89 only all Method.invoke() frames, but also any frames for which the 90 class is a subclass of sun.reflect.MethodAccessorImpl. 91 92 <LI> The JVM entry points JVM_InvokeMethod and 93 JVM_NewInstanceFromConstructor are currently still used because the 94 first invocation of the bytecode-based reflection is currently slower 95 than the original native code. The security checks they perform can, 96 however, be disabled, as they are now performed by Java programming 97 language code. 98 99 </OL> 100 101 </P> 102 <P> 103 104 The following changes were discovered to be necessary for backward 105 compatibility with certain applications (see bug 4474172): 106 107 <OL> 108 109 <LI> The existing JVM entry point JVM_LatestUserDefinedLoader 110 (typically used in applications which rely on the 1.1 security 111 framework) must skip reflection-related frames in its stack walk: 112 specifically all frames associated with subclasses of 113 sun.reflect.MethodAccessorImpl and 114 sun.reflect.ConstructorAccessorImpl. 115 116 <LI> The new reflection implementation can cause class loading to 117 occur in previously-unexpected places (namely during reflective 118 calls). This can cause class loaders which contain subtle bugs to 119 break. In general it is not possible to guarantee complete backward 120 bug compatibility, but one kind of bug has been observed more than 121 once: the inability of a user-defined loader to handle delegation to 122 it for a class it has already loaded. The new reflection 123 implementation is predicated on delegation working properly, as it 124 loads stub classes into newly-fabricated class loaders of type 125 sun.reflect.DelegatingClassLoader, one stub class per loader, to allow 126 unloading of the stub classes to occur more quickly. To handle this 127 kind of bug, the JVM's internal class lookup mechanism must be 128 slightly modified to check for instances of 129 sun.reflect.DelegatingClassLoader as the incoming class loader and 130 silently traverse the "parent" field once for such loaders before 131 entering the bulk of the resolution code. This avoids an upcall to 132 Java programming language code which certain loaders can not handle. 133 134 </OL> 135 136 </P> 137 <P> 138 139 The following JVM entry points may be deleted: 140 141 <UL> 142 <LI> JVM_GetClassFields 143 <LI> JVM_GetClassMethods 144 <LI> JVM_GetClassConstructors 145 <LI> JVM_GetClassField 146 <LI> JVM_GetClassMethod 147 <LI> JVM_GetClassConstructor 148 <LI> JVM_NewInstance 149 <LI> JVM_GetField 150 <LI> JVM_GetPrimitiveField 151 <LI> JVM_SetField 152 <LI> JVM_SetPrimitiveField 153 </UL> 154 155 </P> 156 <P> 157 158 To keep using the previous reflection implementation, licensees should 159 not take changes from Sun's JDK 1.4 relating specifically to the 160 implementation of reflection in the following classes/methods and 161 any associated native code: 162 163 <UL> 164 <LI> java.lang.Class.newInstance0 165 <LI> java.lang.Class.getClassLoader0 166 <LI> java.lang.Class.getFields 167 <LI> java.lang.Class.getMethods 168 <LI> java.lang.Class.getDeclaredFields 169 <LI> java.lang.Class.getDeclaredMethods 170 <LI> java.lang.Class.getFields0 171 <LI> java.lang.Class.getMethods0 172 <LI> java.lang.Class.getConstructors0 173 <LI> java.lang.Class.getField0 174 <LI> java.lang.Class.getMethod0 175 <LI> java.lang.Class.getConstructor0 176 <LI> java.lang.ClassLoader.getCallerClassLoader 177 <LI> java.lang.System.getCallerClass 178 <LI> java.lang.reflect.AccessibleObject 179 <LI> java.lang.reflect.Constructor 180 <LI> java.lang.reflect.Field 181 <LI> java.lang.reflect.Method 182 <LI> java.lang.reflect.Modifier 183 <LI> sun.misc.ClassReflector 184 </UL> 185 186 </P> 187 </HTML>