1 /*
   2  * Copyright (c) 2015, 2016, 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.Path;
  31 import java.nio.file.Paths;
  32 import java.util.concurrent.ConcurrentHashMap;
  33 import java.util.Map;
  34 import java.util.Objects;
  35 
  36 /**
  37  * Factory to get ImageReader
  38  *
  39  * @implNote This class needs to maintain JDK 8 source compatibility.
  40  *
  41  * It is used internally in the JDK to implement jimage/jrtfs access,
  42  * but also compiled and delivered as part of the jrtfs.jar to support access
  43  * to the jimage file provided by the shipped JDK by tools running on JDK 8.
  44  */
  45 public class ImageReaderFactory {
  46     private ImageReaderFactory() {}
  47 
  48     private static final String JAVA_HOME = System.getProperty("java.home");
  49     private static final Path BOOT_MODULES_JIMAGE =
  50         Paths.get(JAVA_HOME, "lib", "modules");
  51 
  52     private static final Map<Path, ImageReader> readers = new ConcurrentHashMap<>();
  53 
  54     /**
  55      * Returns an {@code ImageReader} to read from the given image file
  56      */
  57     public static ImageReader get(Path jimage) throws IOException {
  58         Objects.requireNonNull(jimage);
  59         ImageReader reader = readers.get(jimage);
  60         if (reader != null) {
  61             return reader;
  62         }
  63         reader = ImageReader.open(jimage);
  64         // potential race with other threads opening the same URL
  65         ImageReader r = readers.putIfAbsent(jimage, reader);
  66         if (r == null) {
  67             return reader;
  68         } else {
  69             reader.close();
  70             return r;
  71         }
  72     }
  73 
  74     /**
  75      * Returns the {@code ImageReader} to read the image file in this
  76      * run-time image.
  77      *
  78      * @throws UncheckedIOException if an I/O error occurs
  79      */
  80     public static ImageReader getImageReader() {
  81         try {
  82             return get(BOOT_MODULES_JIMAGE);
  83         } catch (IOException ioe) {
  84             throw new UncheckedIOException(ioe);
  85         }
  86     }
  87 }