1 /*
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 3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 5  * This code is free software; you can redistribute it and/or modify it
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 7  * published by the Free Software Foundation.  Oracle designates this
 8  * particular file as subject to the "Classpath" exception as provided
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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         // A switch, instead of an abstract method, saves 3 subclasses.
60         switch (this) {
61             case DISABLED:
62                 return false;
63             case ENABLED:
64                 return true;
65             case FOR_RUNTIME:
66                 // We want to call jdk.internal.misc.PreviewFeatures.isEnabled(), but
67                 // is not available in older JREs, so we must look to it reflectively.
68                 Class<?> clazz;
69                 try {
70                     clazz = Class.forName("jdk.internal.misc.PreviewFeatures");
71                 } catch (ClassNotFoundException e) {
72                     // It is valid and expected that the class might not exist (JDK-8).
73                     return false;
74                 }
75                 try {
76                     return (Boolean) clazz.getDeclaredMethod("isEnabled").invoke(null);
77                 } catch (NoSuchMethodException | IllegalAccessException |
78                          InvocationTargetException e) {
79                     // But if the class exists, the method must exist and be callable.
80                     throw new ExceptionInInitializerError(e);
81                 }
82             default:
83                 throw new IllegalStateException("Invalid mode: " + this);
84         }
85     }
86 }