--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/test/testlibrary/RedefineClassHelper.java	Mon Jun 02 19:08:18 2014 +0200
@@ -0,0 +1,79 @@
+/*
+ * Copyright (c) 2014, 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.io.PrintWriter;
+import java.lang.instrument.*;
+import com.oracle.java.testlibrary.*;
+
+/*
+ * Helper class to write tests that redefine classes.
+ * When main method is run, it will create a redefineagent.jar that can be used
+ * with the -javaagent option to support redefining classes in jtreg tests.
+ *
+ * See sample test in test/testlibrary_tests/RedefineClassTest.java
+ */
+public class RedefineClassHelper {
+
+    public static Instrumentation instrumentation;
+    public static void premain(String agentArgs, Instrumentation inst) {
+        instrumentation = inst;
+    }
+
+    /**
+     * Redefine a class
+     *
+     * @param clazz Class to redefine
+     * @param javacode String with the new java code for the class to be redefined
+     */
+    public static void redefineClass(Class clazz, String javacode) throws Exception {
+        byte[] bytecode = InMemoryJavaCompiler.compile(clazz.getName(), javacode);
+        redefineClass(clazz, bytecode);
+    }
+
+    /**
+     * Redefine a class
+     *
+     * @param clazz Class to redefine
+     * @param bytecode byte[] with the new class
+     */
+    public static void redefineClass(Class clazz, byte[] bytecode) throws Exception {
+        instrumentation.redefineClasses(new ClassDefinition(clazz, bytecode));
+    }
+
+    /**
+     * Main method to be invoked before test to create the redefineagent.jar
+     */
+    public static void main(String[] args) throws Exception {
+        ClassFileInstaller.main("RedefineClassHelper");
+
+        PrintWriter pw = new PrintWriter("MANIFEST.MF");
+        pw.println("Premain-Class: RedefineClassHelper");
+        pw.println("Can-Redefine-Classes: true");
+        pw.close();
+
+        sun.tools.jar.Main jarTool = new sun.tools.jar.Main(System.out, System.err, "jar");
+        if (!jarTool.run(new String[] { "-cmf", "MANIFEST.MF", "redefineagent.jar", "RedefineClassHelper.class" })) {
+            throw new Exception("jar operation failed");
+        }
+    }
+}