ClassLoader实现热修复的示例

public class MyApplication extends MultiDexApplication {

    @Override
    protected void attachBaseContext(Context base) {
        super.attachBaseContext(base);
        new FixDemo().loadFixedDex(base);
    }
}

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();
        }
    }
}

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;
    }

}