Android 插件化框架Small解析 -- 类的动态加载源码
2019-05-15 本文已影响24人
Android高级工程师
ClassLoader Dex 扩展
在 ApkBundleLauncher.loadBundle 中：
public void loadBundle(Bundle bundle) {
...
// Load dex
final LoadedApk fApk = apk;
Bundle.postIO(new Runnable() {
@Override
public void run() {
try {
fApk.dexFile = DexFile.loadDex(fApk.path, fApk.optDexFile.getPath(), 0);
} catch (IOException e) {
throw new RuntimeException(e);
}
}
});
// Extract native libraries with specify ABI
String libDir = parser.getLibraryDirectory();
if (libDir != null) {
apk.libraryPath = new File(apk.packagePath, libDir);
}
sLoadedApks.put(packageName, apk);
}
这里直接调用了 DexFile.loadDex 来加载 dex 文件并保存到 LoadedApk 对象的 dexFile 变量中。
把 native libraries 路径保存到 LoadedApk.libraryPath 中
然后在 ApkBundleLauncher.postSetUp() 方法中：
public void postSetUp() {
...
String[] dexPaths = new String[N];
DexFile[] dexFiles = new DexFile[N];
// 这里把所有的dex文件保存到一个数组中
for (LoadedApk apk : apks) {
dexPaths[i] = apk.path;
dexFiles[i] = apk.dexFile;
if (Small.getBundleUpgraded(apk.packageName)) {
if (apk.optDexFile.exists()) apk.optDexFile.delete();
Small.setBundleUpgraded(apk.packageName, false);
}
i++;
}
// 扩展当前ClassLoader的DexPathList，把前面解析到的dex添加到 DexPathList.dexElements 中去
ReflectAccelerator.expandDexPathList(cl, dexPaths, dexFiles);
// 把 native library 也保存到数组中
List<File> libPathList = new ArrayList<File>();
for (LoadedApk apk : apks) {
if (apk.libraryPath != null) {
libPathList.add(apk.libraryPath);
}
}
// 扩展当前ClassLoader的DexPathList，把前面解析到的 native library 添加到 DexPathList.nativeLibraryDirectories 中
if (libPathList.size() > 0) {
ReflectAccelerator.expandNativeLibraryDirectories(cl, libPathList);
}
...
}
扩展 DexPathList
这里主要是调用反射扩展当前 ClassLoader 的 DexPathList 的 dexElements 变量。
public static boolean expandDexPathList(ClassLoader cl, String[] dexPaths, DexFile[] dexFiles) {
if (Build.VERSION.SDK_INT < 14) {
return V9_13.expandDexPathList(cl, dexPaths, dexFiles);
} else {
return V14_.expandDexPathList(cl, dexPaths, dexFiles);
}
}
public static boolean expandDexPathList(ClassLoader cl,
String[] dexPaths, DexFile[] dexFiles) {
try {
int N = dexPaths.length;
Object[] elements = new Object[N];
// 这里相当于做了DexPathList.makeElements的工作，生成 Element 数组
for (int i = 0; i < N; i++) {
String dexPath = dexPaths[i];
File pkg = new File(dexPath);
DexFile dexFile = dexFiles[i];
elements[i] = makeDexElement(pkg, dexFile);
}
// 把生成的 Element 数组添加到DexPathList.dexElements中
fillDexPathList(cl, elements);
} catch (Exception e) {
e.printStackTrace();
return false;
}
return true;
}
private static Object makeDexElement(File pkg, boolean isDirectory, DexFile dexFile) throws Exception {
if (sDexElementClass == null) {
sDexElementClass = Class.forName("dalvik.system.DexPathList$Element");
}
if (sDexElementConstructor == null) {
sDexElementConstructor = sDexElementClass.getConstructors()[0];
}
Class<?>[] types = sDexElementConstructor.getParameterTypes();
switch (types.length) {
case 3:
if (types[1].equals(ZipFile.class)) {
// Element(File apk, ZipFile zip, DexFile dex)
ZipFile zip;
try {
zip = new ZipFile(pkg);
} catch (IOException e) {
throw e;
}
try {
return sDexElementConstructor.newInstance(pkg, zip, dexFile);
} catch (Exception e) {
zip.close();
throw e;
}
} else {
// Element(File apk, File zip, DexFile dex)
return sDexElementConstructor.newInstance(pkg, pkg, dexFile);
}
case 4:
default:
// Element(File apk, boolean isDir, File zip, DexFile dex)
if (isDirectory) {
return sDexElementConstructor.newInstance(pkg, true, null, null);
} else {
return sDexElementConstructor.newInstance(pkg, false, pkg, dexFile);
}
}
}
private static void fillDexPathList(ClassLoader cl, Object[] elements)
throws NoSuchFieldException, IllegalAccessException {
if (sPathListField == null) {
sPathListField = getDeclaredField(DexClassLoader.class.getSuperclass(), "pathList");
}
Object pathList = sPathListField.get(cl);
if (sDexElementsField == null) {
sDexElementsField = getDeclaredField(pathList.getClass(), "dexElements");
}
expandArray(pathList, sDexElementsField, elements, true);
}
扩展 NativeLibraryDirectories
这里主要是调用反射扩展当前 ClassLoader 的 DexPathList 的 nativeLibraryDirectories 变量。
public static void expandNativeLibraryDirectories(ClassLoader classLoader, List<File> libPath) {
int v = Build.VERSION.SDK_INT;
if (v < 14) {
V9_13.expandNativeLibraryDirectories(classLoader, libPath);
} else if (v < 23) {
V14_22.expandNativeLibraryDirectories(classLoader, libPath);
} else {
V23_.expandNativeLibraryDirectories(classLoader, libPath);
}
}
public static void expandNativeLibraryDirectories(ClassLoader classLoader,
List<File> libPaths) {
if (sPathListField == null) return;
Object pathList = getValue(sPathListField, classLoader);
if (pathList == null) return;
if (sDexPathList_nativeLibraryDirectories_field == null) {
sDexPathList_nativeLibraryDirectories_field = getDeclaredField(
pathList.getClass(), "nativeLibraryDirectories");
if (sDexPathList_nativeLibraryDirectories_field == null) return;
}
try {
// List<File> nativeLibraryDirectories
List<File> paths = getValue(sDexPathList_nativeLibraryDirectories_field, pathList);
if (paths == null) return;
paths.addAll(libPaths);
// Element[] nativeLibraryPathElements
if (sDexPathList_nativeLibraryPathElements_field == null) {
sDexPathList_nativeLibraryPathElements_field = getDeclaredField(
pathList.getClass(), "nativeLibraryPathElements");
}
if (sDexPathList_nativeLibraryPathElements_field == null) return;
int N = libPaths.size();
Object[] elements = new Object[N];
for (int i = 0; i < N; i++) {
Object dexElement = makeDexElement(libPaths.get(i));
elements[i] = dexElement;
}
expandArray(pathList, sDexPathList_nativeLibraryPathElements_field, elements, false);
} catch (Exception e) {
e.printStackTrace();
}
}
}
## 类的动态加载
把 ClassLoader 扩展以后，就可以在宿主apk里面正常调用插件中的类了。插件类的入口 Activity 我们还是要通过反射来调用的，
