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 }