// DexClassLoader.java
public class DexClassLoader extends BaseDexClassLoader {
 public DexClassLoader(String dexPath, String optimizedDirectory,
  String libraryPath, ClassLoader parent) {
 super(dexPath, new File(optimizedDirectory), libraryPath, parent);
 }
}

// PathClassLoader.java
public class PathClassLoader extends BaseDexClassLoader {
 public PathClassLoader(String dexPath, ClassLoader parent) {
 super(dexPath, null, null, parent);
 }

 public PathClassLoader(String dexPath, String libraryPath,
  ClassLoader parent) {
 super(dexPath, null, libraryPath, parent);
 }
}

public static boolean injectDexAtFirst(String dexPath, String dexOptPath) {

 // 获取系统的dexElements
 Object baseDexElements = getDexElements(getPathList(getPathClassLoader()));

 // 获取patch的dexElements
 DexClassLoader patchDexClassLoader = new DexClassLoader(dexPath, dexOptPath, dexPath, getPathClassLoader());
 Object patchDexElements = getDexElements(getPathList(patchDexClassLoader));

 // 组合最新的dexElements
 Object allDexElements = combineArray(patchDexElements, baseDexElements);

 // 将最新的dexElements添加到系统的classLoader中
 Object pathList = getPathList(getPathClassLoader());
 FieldUtils.writeField(pathList, "dexElements", allDexElements);
}

public static ClassLoader getPathClassLoader() {
 return DexUtils.class.getClassLoader();
}

/**
 * 反射调用getPathList方法，获取数据
 * @param classLoader
 * @return
 * @throws ClassNotFoundException
 * @throws NoSuchFieldException
 * @throws IllegalAccessException
 */
public static Object getPathList(ClassLoader classLoader) throws ClassNotFoundException, NoSuchFieldException, IllegalAccessException {
 return FieldUtils.readField(classLoader, "pathList");
}

/**
 * 反射调用pathList对象的dexElements数据
 * @param pathList
 * @return
 * @throws NoSuchFieldException
 * @throws IllegalAccessException
 */
public static Object getDexElements(Object pathList) throws NoSuchFieldException, IllegalAccessException {
 LogUtils.d("Reflect To Get DexElements");
 return FieldUtils.readField(pathList, "dexElements");
}

/**
 * 拼接dexElements，将patch的dex插入到原来dex的头部
 * @param firstElement
 * @param secondElement
 * @return
 */
public static Object combineArray(Object firstElement, Object secondElement) {

 LogUtils.d("Combine DexElements");

 // 取得一个数组的Class对象, 如果对象是数组，getClass只能返回数组类型，而getComponentType可以返回数组的实际类型
 Class objTypeClass = firstElement.getClass().getComponentType();

 int firstArrayLen = Array.getLength(firstElement);
 int secondArrayLen = Array.getLength(secondElement);
 int allArrayLen = firstArrayLen + secondArrayLen;

 Object allObject = Array.newInstance(objTypeClass, allArrayLen);
 for (int i = 0; i < allArrayLen; i++) {
 if (i < firstArrayLen) {
  Array.set(allObject, i, Array.get(firstElement, i));
 } else {
  Array.set(allObject, i, Array.get(secondElement, i - firstArrayLen));
 }
 }
 return allObject;
}

public static void loadPatchResources(Context context, String apkPath) throws Exception {
 AssetManager newAssetManager = AssetManager.class.newInstance();
 invokeMethod(newAssetManager, "addAssetPath", apkPath);
 invokeMethod(newAssetManager, "ensureStringBlocks");
 replaceAssetManager(context, newAssetManager);
}

private static void replaceAssetManager(Context context, AssetManager newAssetManager)
  throws Exception {
 Collection<WeakReference<Resources>> references;
 if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
 Class<?> resourcesManagerClass = Class.forName("android.app.ResourcesManager");
 Object resourcesManager = invokeStaticMethod(resourcesManagerClass, "getInstance");

 if (getField(resourcesManagerClass, "mActiveResources") != null) {
  ArrayMap<?, WeakReference<Resources>> arrayMap =
   (ArrayMap) readField(resourcesManager, "mActiveResources", true);
  references = arrayMap.values();
 } else {
  references = (Collection) readField(resourcesManager, "mResourceReferences", true);
 }
 } else {
 HashMap<?, WeakReference<Resources>> map =
   (HashMap) readField(ActivityThreadCompat.instance(), "mActiveResources", true);
 references = map.values();
 }

 AssetManager assetManager = context != null ? context.getAssets() : null;
 for (WeakReference<Resources> wr : references) {
 Resources resources = wr.get();
 if (resources == null) continue;

 try {
  writeField(resources, "mAssets", newAssetManager);
  originalAssetManager = assetManager;
 } catch (Throwable ignore) {
  Object resourceImpl = readField(resources, "mResourcesImpl", true);
  writeField(resourceImpl, "mAssets", newAssetManager);
 }

 resources.updateConfiguration(resources.getConfiguration(),
   resources.getDisplayMetrics());
 }

 if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
 for (WeakReference<Resources> wr : references) {
  Resources resources = wr.get();
  if (resources == null) continue;

  // android.util.Pools$SynchronizedPool<TypedArray>
  Object typedArrayPool = readField(resources, "mTypedArrayPool", true);

  // Clear all the pools
  while (invokeMethod(typedArrayPool, "acquire") != null) ;
 }
 }
}