ClassWriter cw = new ClassWriter(0);
cw.visit(Opcodes.V1_8, Opcodes.ACC_PUBLIC, "Example", null, "java/lang/Object", null);
MethodVisitor mv = cw.visitMethod(Opcodes.ACC_PUBLIC, "<init>", "()V", null, null);
mv.visitVarInsn(Opcodes.ALOAD, 0);
mv.visitMethodInsn(Opcodes.INVOKESPECIAL, "java/lang/Object", "<init>", "()V", false);
mv.visitInsn(Opcodes.RETURN);
mv.visitMaxs(1, 1);
mv.visitEnd();
cw.visitEnd();
byte[] bytecode = cw.toByteArray();
ClassLoader loader = new ByteArrayClassLoader();
Class<?> exampleClass = loader.defineClass("Example", bytecode);
ClassReader cr = new ClassReader(exampleClass);
ClassNode cn = new ClassNode();
cr.accept(cn, 0);
for (MethodNode mn : cn.methods) {
if (mn.name.equals("exampleMethod")) {
InsnList instructions = new InsnList();
instructions.add(new FieldInsnNode(Opcodes.GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;"));
instructions.add(new LdcInsnNode("Hello, World!"));
instructions.add(new MethodInsnNode(Opcodes.INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V", false));
mn.instructions.insert(instructions);
}
}
ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS);
cn.accept(cw);
byte[] modifiedBytecode = cw.toByteArray();
ClassLoader modifiedLoader = new ByteArrayClassLoader();
Class<?> modifiedClass = modifiedLoader.defineClass("Example", modifiedBytecode);
ClassWriter cw = new ClassWriter(0);
cw.visit(Opcodes.V1_8, Opcodes.ACC_PUBLIC, "Proxy", null, "Example", null);
MethodVisitor mv = cw.visitMethod(Opcodes.ACC_PUBLIC, "<init>", "()V", null, null);
mv.visitVarInsn(Opcodes.ALOAD, 0);
mv.visitMethodInsn(Opcodes.INVOKESPECIAL, "Example", "<init>", "()V", false);
mv.visitInsn(Opcodes.RETURN);
mv.visitMaxs(1, 1);
mv.visitEnd();
cw.visitEnd();
byte[] bytecode = cw.toByteArray();
ClassLoader loader = new ByteArrayClassLoader();
Class<?> proxyClass = loader.defineClass("Proxy", bytecode);
