1 /*
2 * Copyright (c) 2025, 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 package jdk.internal.jimage;
26
27 import java.lang.reflect.InvocationTargetException;
28
29 /**
30 * Specifies the preview mode used to open a jimage file via {@link ImageReader}.
31 *
32 * @implNote This class needs to maintain JDK 8 source compatibility.
33 *
34 * It is used internally in the JDK to implement jimage/jrtfs access,
35 * but also compiled and delivered as part of the jrtfs.jar to support access
36 * to the jimage file provided by the shipped JDK by tools running on JDK 8.
37 * */
38 public enum PreviewMode {
39 /**
40 * Preview mode is disabled. No preview classes or resources will be available
41 * in this mode.
42 */
43 DISABLED,
44 /**
45 * Preview mode is enabled. If preview classes or resources exist in the jimage file,
46 * they will be made available.
47 */
48 ENABLED,
49 /**
50 * The preview mode of the current run-time, typically determined by the
51 * {@code --enable-preview} flag.
52 */
53 FOR_RUNTIME;
54
55 /**
56 * Resolves whether preview mode should be enabled for an {@link ImageReader}.
57 */
58 public boolean isPreviewModeEnabled() {
59 if (!DISABLE_PREVIEW_PATCHING) {
60 return false;
61 }
62 // A switch, instead of an abstract method, saves 3 subclasses.
63 switch (this) {
64 case DISABLED:
65 return false;
66 case ENABLED:
67 return true;
68 case FOR_RUNTIME:
69 // We want to call jdk.internal.misc.PreviewFeatures.isEnabled(), but
70 // is not available in older JREs, so we must look to it reflectively.
71 Class<?> clazz;
72 try {
73 clazz = Class.forName("jdk.internal.misc.PreviewFeatures");
74 } catch (ClassNotFoundException e) {
75 // It is valid and expected that the class might not exist (JDK-8).
76 return false;
77 }
78 try {
79 return (Boolean) clazz.getDeclaredMethod("isEnabled").invoke(null);
80 } catch (NoSuchMethodException | IllegalAccessException |
81 InvocationTargetException e) {
82 // But if the class exists, the method must exist and be callable.
83 throw new ExceptionInInitializerError(e);
84 }
85 default:
86 throw new IllegalStateException("Invalid mode: " + this);
87 }
88 }
89
90 // Temporary system property to disable preview patching and enable the new preview mode
91 // feature for testing/development. Once the preview mode feature is finished, the value
92 // will be always 'true' and this code, and all related dead-code can be removed.
93 private static final boolean DISABLE_PREVIEW_PATCHING_DEFAULT = false;
94 private static final boolean DISABLE_PREVIEW_PATCHING = Boolean.parseBoolean(
95 System.getProperty(
96 "DISABLE_PREVIEW_PATCHING",
97 Boolean.toString(DISABLE_PREVIEW_PATCHING_DEFAULT)));
98 }