01: /*
02: * Copyright 2001 Sun Microsystems, Inc. All Rights Reserved.
03: * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
04: *
05: * This code is free software; you can redistribute it and/or modify it
06: * under the terms of the GNU General Public License version 2 only, as
07: * published by the Free Software Foundation. Sun designates this
08: * particular file as subject to the "Classpath" exception as provided
09: * 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 sun.reflect;
27:
28: import java.security.AccessController;
29: import java.security.PrivilegedAction;
30: import sun.misc.Unsafe;
31:
32: /** Utility class which assists in calling Unsafe.defineClass() by
33: creating a new class loader which delegates to the one needed in
34: order for proper resolution of the given bytecodes to occur. */
35:
36: class ClassDefiner {
37: static final Unsafe unsafe = Unsafe.getUnsafe();
38:
39: /** <P> We define generated code into a new class loader which
40: delegates to the defining loader of the target class. It is
41: necessary for the VM to be able to resolve references to the
42: target class from the generated bytecodes, which could not occur
43: if the generated code was loaded into the bootstrap class
44: loader. </P>
45:
46: <P> There are two primary reasons for creating a new loader
47: instead of defining these bytecodes directly into the defining
48: loader of the target class: first, it avoids any possible
49: security risk of having these bytecodes in the same loader.
50: Second, it allows the generated bytecodes to be unloaded earlier
51: than would otherwise be possible, decreasing run-time
52: footprint. </P>
53: */
54: static Class defineClass(String name, byte[] bytes, int off,
55: int len, final ClassLoader parentClassLoader) {
56: ClassLoader newLoader = (ClassLoader) AccessController
57: .doPrivileged(new PrivilegedAction() {
58: public Object run() {
59: return new DelegatingClassLoader(
60: parentClassLoader);
61: }
62: });
63: return unsafe.defineClass(name, bytes, off, len, newLoader,
64: null);
65: }
66: }
67:
68: // NOTE: this class's name and presence are known to the virtual
69: // machine as of the fix for 4474172.
70: class DelegatingClassLoader extends ClassLoader {
71: DelegatingClassLoader(ClassLoader parent) {
72: super(parent);
73: }
74: }
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