src/java.base/share/classes/jdk/internal/jimage/ImageReaderFactory.java

/*
 * Copyright (c) 2015, 2024, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
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package jdk.internal.jimage;

import java.io.IOException;
import java.io.UncheckedIOException;
import java.nio.file.FileSystem;
import java.nio.file.FileSystems;
import java.nio.file.Path;
import java.util.concurrent.ConcurrentHashMap;
import java.util.Map;
import java.util.Objects;
import java.util.function.Function;

/**
 * Factory to get ImageReader
 *
 * @implNote This class needs to maintain JDK 8 source compatibility.
 *
 * It is used internally in the JDK to implement jimage/jrtfs access,
 * but also compiled and delivered as part of the jrtfs.jar to support access
 * to the jimage file provided by the shipped JDK by tools running on JDK 8.
 */
public class ImageReaderFactory {
    private ImageReaderFactory() {}

    private static final String JAVA_HOME = System.getProperty("java.home");
    private static final Path BOOT_MODULES_JIMAGE;

    static {
        FileSystem fs;
        if (ImageReaderFactory.class.getClassLoader() == null) {
            try {
                fs = (FileSystem) Class.forName("sun.nio.fs.DefaultFileSystemProvider")
                        .getMethod("theFileSystem")
                        .invoke(null);
            } catch (Exception e) {
                throw new ExceptionInInitializerError(e);
            }
        } else {
            fs = FileSystems.getDefault();
        }
        BOOT_MODULES_JIMAGE = fs.getPath(JAVA_HOME, "lib", "modules");
    }

    private static final Map<Path, ImageReader> readers = new ConcurrentHashMap<>();

    /**
     * Returns an {@code ImageReader} to read from the given image file
     */
    public static ImageReader get(Path jimage) throws IOException {
        Objects.requireNonNull(jimage);
        try {
            return readers.computeIfAbsent(jimage, OPENER);
        } catch (UncheckedIOException io) {
            throw io.getCause();
        }
    }

    private static Function<Path, ImageReader> OPENER = new Function<Path, ImageReader>() {
        public ImageReader apply(Path path) {
            try {
                return ImageReader.open(path);
            } catch (IOException io) {
                throw new UncheckedIOException(io);
            }
        }
    };

    /**
     * Returns the {@code ImageReader} to read the image file in this
     * run-time image.
     *
     * @throws UncheckedIOException if an I/O error occurs
     */
    public static ImageReader getImageReader() {
        try {
            return get(BOOT_MODULES_JIMAGE);
        } catch (IOException ioe) {
            throw new UncheckedIOException(ioe);
        }
    }
}