1 /*
 2  * Copyright (c) 2015, 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 
26 package jdk.internal.jimage;
27 
28 import java.io.IOException;
29 import java.io.UncheckedIOException;
30 import java.nio.file.FileSystem;
31 import java.nio.file.FileSystems;
32 
33 /**
34  * Static holder class for singleton {@link ImageReader} instance.
35  *
36  * @implNote This class needs to maintain JDK 8 source compatibility.
37  *
38  * It is used internally in the JDK to implement jimage/jrtfs access,
39  * but also compiled and delivered as part of the jrtfs.jar to support access
40  * to the jimage file provided by the shipped JDK by tools running on JDK 8.
41  */
42 public class SystemImageReader {
43     private static final ImageReader SYSTEM_IMAGE_READER;
44 
45     static {
46         String javaHome = System.getProperty("java.home");
47         FileSystem fs;
48         if (SystemImageReader.class.getClassLoader() == null) {
49             try {
50                 fs = (FileSystem) Class.forName("sun.nio.fs.DefaultFileSystemProvider")
51                         .getMethod("theFileSystem")
52                         .invoke(null);
53             } catch (Exception e) {
54                 throw new ExceptionInInitializerError(e);
55             }
56         } else {
57             fs = FileSystems.getDefault();
58         }
59         try {
60             SYSTEM_IMAGE_READER = ImageReader.open(fs.getPath(javaHome, "lib", "modules"), PreviewMode.FOR_RUNTIME);
61         } catch (IOException e) {
62             throw new ExceptionInInitializerError(e);
63         }
64     }
65 
66     /**
67      * Returns the singleton {@code ImageReader} to read the image file in this
68      * run-time image. The returned instance must not be closed.
69      *
70      * @throws UncheckedIOException if an I/O error occurs
71      */
72     public static ImageReader get() {
73         return SYSTEM_IMAGE_READER;
74     }
75 
76     /**
77      * Returns the "raw" API for accessing underlying jimage resource entries.
78      *
79      * <p>This is only meaningful for use by code dealing directly with jimage
80      * files, and cannot be used to reliably lookup resources used at runtime.
81      */
82     public static ResourceEntries getResourceEntries() {
83         return get().getResourceEntries();
84     }
85 
86     private SystemImageReader() {}
87 }