1 /*
   2  * Copyright (c) 2017, 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 import java.util.*;
  25 import java.io.*;
  26 
  27 public class PreemptingClassLoader extends ClassLoader {
  28 
  29     private final Set<String> names = new HashSet<>();
  30     boolean checkLoaded = true;
  31 
  32     public PreemptingClassLoader(String... names) {
  33         for (String n : names) this.names.add(n);
  34     }
  35 
  36     public PreemptingClassLoader(String name, String[] names) {
  37         super(name, ClassLoader.getSystemClassLoader());
  38         for (String n : names) this.names.add(n);
  39     }
  40 
  41     public PreemptingClassLoader(String name, String[] names, boolean cL) {
  42         super(name, ClassLoader.getSystemClassLoader());
  43         for (String n : names) this.names.add(n);
  44         checkLoaded = cL;
  45     }
  46 
  47     protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
  48         if (!names.contains(name)) return super.loadClass(name, resolve);
  49         Class<?> result = checkLoaded ? findLoadedClass(name) : null;
  50         if (result == null) {
  51             String filename = name.replace('.', '/') + ".class";
  52             try (InputStream data = getResourceAsStream(filename)) {
  53                 if (data == null) throw new ClassNotFoundException();
  54                 try (ByteArrayOutputStream buffer = new ByteArrayOutputStream()) {
  55                     int b;
  56                     do {
  57                         b = data.read();
  58                         if (b >= 0) buffer.write(b);
  59                     } while (b >= 0);
  60                     byte[] bytes = buffer.toByteArray();
  61                     result = defineClass(name, bytes, 0, bytes.length);
  62                 }
  63             } catch (IOException e) {
  64                 throw new ClassNotFoundException("Error reading class file", e);
  65             }
  66         }
  67         if (resolve) resolveClass(result);
  68         return result;
  69     }
  70 
  71 }