import org.objectweb.asm.ClassWriter; import org.objectweb.asm.Type; import org.objectweb.asm.commons.Method; public class ReflectASMExample { public static void main(String[] args) throws Exception { ClassWriter cw = new ClassWriter(0); cw.visit(Opcodes.V1_8, Opcodes.ACC_PUBLIC, "ReflectASMExample", null, Type.getInternalName(Object.class), null); MethodVisitor constructor = cw.visitMethod(Opcodes.ACC_PUBLIC, "<init>", "()V", null, null); constructor.visitVarInsn(Opcodes.ALOAD, 0); constructor.visitMethodInsn(Opcodes.INVOKESPECIAL, Type.getInternalName(Object.class), "<init>", "()V", false); constructor.visitInsn(Opcodes.RETURN); constructor.visitMaxs(1, 1); constructor.visitEnd(); MethodVisitor method = cw.visitMethod(Opcodes.ACC_PUBLIC + Opcodes.ACC_STATIC, "sayHello", "()V", null, null); method.visitFieldInsn(Opcodes.GETSTATIC, Type.getInternalName(System.class), "out", Type.getDescriptor(PrintStream.class)); method.visitLdcInsn("Hello ReflectASM!"); method.visitMethodInsn(Opcodes.INVOKEVIRTUAL, Type.getInternalName(PrintStream.class), "println", "(Ljava/lang/String;)V", false); method.visitInsn(Opcodes.RETURN); method.visitMaxs(2, 0); method.visitEnd(); byte[] classData = cw.toByteArray(); ClassLoader classLoader = new ClassLoader() { protected Class<?> findClass(String name) throws ClassNotFoundException { if (name.equals("ReflectASMExample")) { return defineClass(name, classData, 0, classData.length); } return super.findClass(name); } }; Class<?> clazz = classLoader.loadClass("ReflectASMExample"); Object instance = clazz.newInstance(); Method sayHelloMethod = clazz.getDeclaredMethod("sayHello"); sayHelloMethod.invoke(instance); } }