 <p>If you dont want to use an external library, you need to write your own ClassLoader. The most simple implementation i found is <a href="https://kenai.com/projects/btrace/sources/hg/content/src/share/classes/com/sun/btrace/MemoryClassLoader.java?rev=452" rel="nofollow">here</a>.</p> <pre><code>/* * Copyright 2008-2010 Sun Microsystems, Inc. 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. Sun designates this * particular file as subject to the "Classpath" exception as provided * by Sun in the LICENSE file that accompanied this code. * * 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, * CA 95054 USA or visit www.sun.com if you need additional information or * have any questions. */ package com.sun.btrace; /** * A simple class loader that loads from byte buffer. * * @author A. Sundararajan */ final class MemoryClassLoader extends ClassLoader { MemoryClassLoader() { this(null); } MemoryClassLoader(ClassLoader parent) { super(parent); } Class loadClass(String className, byte[] buf) throws ClassNotFoundException { return defineClass(className, buf, 0, buf.length); } } </code></pre>