--- /dev/null	2017-08-03 13:42:08.516000218 -0400
+++ new/test/hotspot/jtreg/runtime/LoaderConstraints/common/PreemptingClassLoader.java	2017-09-25 11:09:16.627627455 -0400
@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) 2017, 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.
+ *
+ * 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,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+import java.util.*;
+import java.io.*;
+
+public class PreemptingClassLoader extends ClassLoader {
+
+    private final Set<String> names = new HashSet<>();
+  
+    public PreemptingClassLoader(String... names) {
+        for (String n : names) this.names.add(n);
+    }
+  
+    protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
+        if (!names.contains(name)) return super.loadClass(name, resolve);
+        Class<?> result = findLoadedClass(name);
+        if (result == null) {
+            String filename = name.replace('.', '/') + ".class";
+            try (InputStream data = getResourceAsStream(filename)) {
+                if (data == null) throw new ClassNotFoundException();
+                try (ByteArrayOutputStream buffer = new ByteArrayOutputStream()) {
+                    int b;
+                    do {
+                        b = data.read();
+                        if (b >= 0) buffer.write(b);
+                    } while (b >= 0);
+                    byte[] bytes = buffer.toByteArray();
+                    result = defineClass(name, bytes, 0, bytes.length);
+                }
+            } catch (IOException e) {
+                throw new ClassNotFoundException("Error reading class file", e);
+            }
+        }
+        if (resolve) resolveClass(result);
+        return result;
+    }
+
+}