ClassLoader实现热修复的示例

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效果图

修复之前
修复之后

实现思路

主要实现思路主要是:

  • 先编写一个有 bug 的程序, 运行安装到手机。

  • 修正bug之后,重新 rebuild, 然后找到 app - build - intermediates - dex - debug - mergeProjectDexDebug - out - classes.dex 移动到 修复包 下载的目录 , 这里放在 assets 目录下,并重命名 classes.dexclasses2.dex

    base on AndroidStudio 3.5.1

  • 然后点击程序上的 Move Dex, 将修正bug之后的dex包 移动到 android/data/packagename/ 目录下,在这里目录才有加载dex权限

  • 然后重启程序,在继承自 MultiDexApplicationApplication 中加载对应的 dex 文件,获取对应的dexElements,然后合并到应用的dexElements之前。


相关代码

demo 源码下载
demo.apk download

  • MyApplication

    public class MyApplication extends MultiDexApplication {
    
        @Override
        protected void attachBaseContext(Context base) {
            super.attachBaseContext(base);
            new FixDemo().loadFixedDex(base);
        }
    }
    
  • MainActivity

    public class MainActivity extends AppCompatActivity {
        private TextView bugTv;
        private int i = 10;
        private int a = 0;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
    
            bugTv = findViewById(R.id.bug);
    
            bugTv.setText("Bug: " + i + " / " + a);
    
            findViewById(R.id.bug).setOnClickListener(v -> bugMethod());
            findViewById(R.id.move).setOnClickListener(v -> moveDex("classes2.dex"));
        }
    
        private void bugMethod() {
            Toast.makeText(this, "res = " + i / a, Toast.LENGTH_SHORT).show();
        }
    
    
        private void moveDex(String name) {
            //目录 data/data/packageName/odex
            File fileDir = getDir(FixDemo.DEX_DIR, Context.MODE_PRIVATE);
            AssetManager am = getResources().getAssets();
            try {
                InputStream is = am.open(name);
                String filePath = fileDir.getAbsolutePath() + File.separator + name;
                File file = new File(filePath);
                if (file.exists()) {
                    file.delete();
                }
                FileOutputStream os = new FileOutputStream(filePath);
                int len;
                byte[] buffer = new byte[1024];
                while ((len = is.read(buffer)) != -1) {
                    os.write(buffer, 0, len);
                }
                os.close();
                is.close();
    
                //粘贴完文件
                File f = new File(filePath);
                if (f.exists()) {
                    //文件从sk卡赋值到应用运行目录下,成功则toast提示
                    Toast.makeText(this, "dex移动成功,请重启应用", Toast.LENGTH_SHORT).show();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    
  • FixDemo

    public class FixDemo {
    
        public static String DEX_DIR = "odex";
    
        private File odexDir;
    
        /**
         * 开始替换dex
         */
        public void loadFixedDex(Context context) {
            if (null == context) {
                return;
            }
            //遍历所有的修复的dex
            odexDir = context.getDir(DEX_DIR, Context.MODE_PRIVATE);
            File[] listFiles = odexDir.listFiles();
            if (listFiles == null) {
                return;
            }
            HashSet<File> loadedDex = new HashSet<>();
            for (File file : listFiles) {
                if (file.getName().startsWith("classes") || file.getName().endsWith(".dex")) {
                    //先将补丁文件放到一个集合里,然后再进行合并
                    loadedDex.add(file);
                }
            }
            //dex合并
            doDexInject(context, loadedDex);
        }
    
        /**
         * dex 合并
         */
        private void doDexInject(Context appContext, HashSet<File> loadedDex) {
            try {
                String filesDirPath = odexDir.getAbsolutePath() + File.separator + "opt_dex";
                File fopt = new File(filesDirPath);
                if (!fopt.exists()) {
                    fopt.mkdir();
                }
                //1.加载应用程序的dex
                BaseDexClassLoader pathLoader = (BaseDexClassLoader) appContext.getClassLoader();
                for (File dex : loadedDex) {
                    //2.加载指定的修复的dex文件
                    DexClassLoader classLoader = new DexClassLoader(
                            dex.getAbsolutePath(),
                            fopt.getAbsolutePath(),
                            null,
                            pathLoader);
                    //3.合并
                    Object dexObj = getPathList(classLoader);
                    Object pathObj = getPathList(pathLoader);
                    Object mDexElementsList = getDexElements(dexObj);
                    Object pathDexElementsList = getDexElements(pathObj);
                    //将两个list合并为一个
                    Object dexElements = combineArray(mDexElementsList, pathDexElementsList);
                    //重写给PathList里面的Element[] dexElements赋值
                    Object pathList = getPathList(pathLoader);
                    ReflectUtils.setClassFiled(pathList, pathList.getClass(), "dexElements", dexElements);
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    
        private Object getPathList(ClassLoader classLoader) {
            try {
                return ReflectUtils.getDeclaredField(classLoader, Class.forName("dalvik.system.BaseDexClassLoader"), "pathList");
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
                return null;
            }
        }
    
        private Object getDexElements(Object obj) {
            return ReflectUtils.getClassField(obj, "dexElements");
        }
    
        /**
         * 合并数组
         */
        private Object combineArray(Object arrayLbs, Object arrayRhs) {
            Class localClass = arrayLbs.getClass().getComponentType();
            int i = Array.getLength(arrayLbs);
            int j = i + Array.getLength(arrayRhs);
            Object result = Array.newInstance(localClass, j);
            for (int k = 0; k < j; ++k) {
                if (k < i) {
                    Array.set(result, k, Array.get(arrayLbs, k));
                } else {
                    Array.set(result, k, Array.get(arrayRhs, k - i));
                }
            }
            return result;
        }
    
    }
    

以上