1 /*
   2  * Copyright (c) 2018, 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.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 package pkg;
  26 
  27 import java.util.*;
  28 import java.io.*;
  29 
  30 // This class loader loads Foo and Parent and calls back to l1 to load Grand.
  31 public class ClassLoaderForParentFoo extends ClassLoader {
  32 
  33     private final Set<String> names = new HashSet<>();
  34 
  35     ClassLoader l1;
  36 
  37     public ClassLoaderForParentFoo(ClassLoader l, String... names) {
  38         l1 = l;
  39         for (String n : names) this.names.add(n);
  40     }
  41 
  42     protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
  43         if (name.contains("Grand")) return l1.loadClass("pkg.Grand");
  44         if (!names.contains(name)) return super.loadClass(name, resolve);
  45         Class<?> result = findLoadedClass(name);
  46         if (result == null) {
  47             // Load our own version of Foo that will be referenced by Parent.
  48             if (name.contains("Parent")) loadClass("pkg.Foo", resolve);
  49             String filename = name.replace('.', '/') + ".class";
  50             try (InputStream data = getResourceAsStream(filename)) {
  51                 if (data == null) throw new ClassNotFoundException();
  52                 try (ByteArrayOutputStream buffer = new ByteArrayOutputStream()) {
  53                     int b;
  54                     do {
  55                         b = data.read();
  56                         if (b >= 0) buffer.write(b);
  57                     } while (b >= 0);
  58                     byte[] bytes = buffer.toByteArray();
  59                     result = defineClass(name, bytes, 0, bytes.length);
  60                 }
  61             } catch (IOException e) {
  62                 throw new ClassNotFoundException("Error reading class file", e);
  63             }
  64         }
  65         if (resolve) resolveClass(result);
  66         return result;
  67     }
  68 
  69 }