diff --git a/runtime/openjdkjvmti/transform.cc b/runtime/openjdkjvmti/transform.cc
index f545125..2809cb6 100644
--- a/runtime/openjdkjvmti/transform.cc
+++ b/runtime/openjdkjvmti/transform.cc
@@ -38,6 +38,7 @@
 #include "class_linker.h"
 #include "dex_file.h"
 #include "dex_file_types.h"
+#include "events-inl.h"
 #include "gc_root-inl.h"
 #include "globals.h"
 #include "jni_env_ext-inl.h"
@@ -52,12 +53,76 @@
 #include "scoped_thread_state_change-inl.h"
 #include "stack.h"
 #include "thread_list.h"
+#include "ti_redefine.h"
 #include "transform.h"
 #include "utf.h"
 #include "utils/dex_cache_arrays_layout-inl.h"
 
 namespace openjdkjvmti {
 
+jvmtiError Transformer::RetransformClassesDirect(
+      ArtJvmTiEnv* env,
+      art::Thread* self,
+      /*in-out*/std::vector<ArtClassDefinition>* definitions) {
+  for (ArtClassDefinition& def : *definitions) {
+    jint new_len = -1;
+    unsigned char* new_data = nullptr;
+    // Static casts are so that we get the right template initialization for the special event
+    // handling code required by the ClassFileLoadHooks.
+    gEventHandler.DispatchEvent(self,
+                                ArtJvmtiEvent::kClassFileLoadHookRetransformable,
+                                GetJniEnv(env),
+                                static_cast<jclass>(def.klass),
+                                static_cast<jobject>(def.loader),
+                                static_cast<const char*>(def.name.c_str()),
+                                static_cast<jobject>(def.protection_domain),
+                                static_cast<jint>(def.dex_len),
+                                static_cast<const unsigned char*>(def.dex_data.get()),
+                                static_cast<jint*>(&new_len),
+                                static_cast<unsigned char**>(&new_data));
+    def.SetNewDexData(env, new_len, new_data);
+  }
+  return OK;
+}
+
+jvmtiError Transformer::RetransformClasses(ArtJvmTiEnv* env,
+                                           art::Runtime* runtime,
+                                           art::Thread* self,
+                                           jint class_count,
+                                           const jclass* classes,
+                                           /*out*/std::string* error_msg) {
+  if (env == nullptr) {
+    *error_msg = "env was null!";
+    return ERR(INVALID_ENVIRONMENT);
+  } else if (class_count < 0) {
+    *error_msg = "class_count was less then 0";
+    return ERR(ILLEGAL_ARGUMENT);
+  } else if (class_count == 0) {
+    // We don't actually need to do anything. Just return OK.
+    return OK;
+  } else if (classes == nullptr) {
+    *error_msg = "null classes!";
+    return ERR(NULL_POINTER);
+  }
+  // A holder that will Deallocate all the class bytes buffers on destruction.
+  std::vector<ArtClassDefinition> definitions;
+  jvmtiError res = OK;
+  for (jint i = 0; i < class_count; i++) {
+    ArtClassDefinition def;
+    res = FillInTransformationData(env, classes[i], &def);
+    if (res != OK) {
+      return res;
+    }
+    definitions.push_back(std::move(def));
+  }
+  res = RetransformClassesDirect(env, self, &definitions);
+  if (res != OK) {
+    return res;
+  }
+  return Redefiner::RedefineClassesDirect(env, runtime, self, definitions, error_msg);
+}
+
+// TODO Move this somewhere else, ti_class?
 jvmtiError GetClassLocation(ArtJvmTiEnv* env, jclass klass, /*out*/std::string* location) {
   JNIEnv* jni_env = nullptr;
   jint ret = env->art_vm->GetEnv(reinterpret_cast<void**>(&jni_env), JNI_VERSION_1_1);
@@ -73,42 +138,61 @@
   return OK;
 }
 
-// TODO Move this function somewhere more appropriate.
-// Gets the data surrounding the given class.
-jvmtiError GetTransformationData(ArtJvmTiEnv* env,
-                                 jclass klass,
-                                 /*out*/std::string* location,
-                                 /*out*/JNIEnv** jni_env_ptr,
-                                 /*out*/jobject* loader,
-                                 /*out*/std::string* name,
-                                 /*out*/jobject* protection_domain,
-                                 /*out*/jint* data_len,
-                                 /*out*/unsigned char** dex_data) {
-  jint ret = env->art_vm->GetEnv(reinterpret_cast<void**>(jni_env_ptr), JNI_VERSION_1_1);
-  if (ret != JNI_OK) {
-    // TODO Different error might be better?
-    return ERR(INTERNAL);
-  }
-  JNIEnv* jni_env = *jni_env_ptr;
-  art::ScopedObjectAccess soa(jni_env);
-  art::StackHandleScope<3> hs(art::Thread::Current());
-  art::Handle<art::mirror::Class> hs_klass(hs.NewHandle(soa.Decode<art::mirror::Class>(klass)));
-  *loader = soa.AddLocalReference<jobject>(hs_klass->GetClassLoader());
-  *name = art::mirror::Class::ComputeName(hs_klass)->ToModifiedUtf8();
-  // TODO is this always null?
-  *protection_domain = nullptr;
-  const art::DexFile& dex = hs_klass->GetDexFile();
-  *location = dex.GetLocation();
-  *data_len = static_cast<jint>(dex.Size());
-  // TODO We should maybe change env->Allocate to allow us to mprotect this memory and stop writes.
-  jvmtiError alloc_error = env->Allocate(*data_len, dex_data);
+// TODO Implement this for real once transformed dex data is actually saved.
+jvmtiError Transformer::GetDexDataForRetransformation(ArtJvmTiEnv* env,
+                                                      art::Handle<art::mirror::Class> klass,
+                                                      /*out*/jint* dex_data_len,
+                                                      /*out*/unsigned char** dex_data) {
+  // TODO De-quicken the dex file before passing it to the agents.
+  LOG(WARNING) << "Dex file is not de-quickened yet! Quickened dex instructions might be present";
+  LOG(WARNING) << "Caching of initial dex data is not yet performed! Dex data might have been "
+               << "transformed by agent already";
+  const art::DexFile& dex = klass->GetDexFile();
+  *dex_data_len = static_cast<jint>(dex.Size());
+  unsigned char* new_dex_data = nullptr;
+  jvmtiError alloc_error = env->Allocate(*dex_data_len, &new_dex_data);
   if (alloc_error != OK) {
     return alloc_error;
   }
   // Copy the data into a temporary buffer.
-  memcpy(reinterpret_cast<void*>(*dex_data),
-          reinterpret_cast<const void*>(dex.Begin()),
-          *data_len);
+  memcpy(reinterpret_cast<void*>(new_dex_data),
+         reinterpret_cast<const void*>(dex.Begin()),
+         *dex_data_len);
+  *dex_data = new_dex_data;
+  return OK;
+}
+
+// TODO Move this function somewhere more appropriate.
+// Gets the data surrounding the given class.
+// TODO Make this less magical.
+jvmtiError Transformer::FillInTransformationData(ArtJvmTiEnv* env,
+                                                 jclass klass,
+                                                 ArtClassDefinition* def) {
+  JNIEnv* jni_env = GetJniEnv(env);
+  if (jni_env == nullptr) {
+    // TODO Different error might be better?
+    return ERR(INTERNAL);
+  }
+  art::ScopedObjectAccess soa(jni_env);
+  art::StackHandleScope<3> hs(art::Thread::Current());
+  art::Handle<art::mirror::Class> hs_klass(hs.NewHandle(soa.Decode<art::mirror::Class>(klass)));
+  if (hs_klass.IsNull()) {
+    return ERR(INVALID_CLASS);
+  }
+  def->klass = klass;
+  def->loader = soa.AddLocalReference<jobject>(hs_klass->GetClassLoader());
+  def->name = art::mirror::Class::ComputeName(hs_klass)->ToModifiedUtf8();
+  // TODO is this always null?
+  def->protection_domain = nullptr;
+  if (def->dex_data.get() == nullptr) {
+    unsigned char* new_data;
+    jvmtiError res = GetDexDataForRetransformation(env, hs_klass, &def->dex_len, &new_data);
+    if (res == OK) {
+      def->dex_data = MakeJvmtiUniquePtr(env, new_data);
+    } else {
+      return res;
+    }
+  }
   return OK;
 }