在接收到ACTION_MEDIA_EJECT或者ACTION_MEDIA_UNMOUNTED广播后，可以通过以下步骤使U盘成功卸载，不会再下次插入的时候系统提示“vold : ForceUnmount failed: Device or resource busy”： 停止对U盘中工厂apk的读写操作，即关闭工厂apk应用程序。 关闭U盘中工厂apk应用程序所打开的所有文件和流。 关闭U盘中工厂apk应用程序所占用的所有资源。 等待一段时间，确保U盘中工厂apk应用程序已经完全释放了对U盘的占用。 卸载U盘。 另外，为了避免下次插入时提示“vold : ForceUnmount failed: Device or resource busy”，可以在卸载U盘后，检查U盘是否已经完全卸载，如果没有完全卸载，可以尝试强制卸载U盘。如果还是不行，可以重启设备再尝试卸载。 请详细写出代码实现方式

以下是示例代码实现方式：

public class MainActivity extends AppCompatActivity {

    private static final String FACTORY_APK_NAME = "factory.apk";
    private static final String FACTORY_APK_PACKAGE_NAME = "com.example.factory";
    private static final int WAIT_TIME = 5000; // 等待时间，单位为毫秒

    private boolean mIsFactoryApkRunning = false;
    private boolean mIsUninstalling = false;

    private BroadcastReceiver mUsbReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            switch (intent.getAction()) {
                case Intent.ACTION_MEDIA_MOUNTED:
                    // 获取U盘中的工厂apk信息
                    String apkPath = getFactoryApkPath(context);
                    if (apkPath != null) {
                        // 启动工厂apk
                        startFactoryApk(context, apkPath);
                    }
                    break;
                case Intent.ACTION_MEDIA_EJECT:
                case Intent.ACTION_MEDIA_UNMOUNTED:
                    // 停止工厂apk
                    stopFactoryApk(context);
                    // 卸载U盘
                    uninstallUsb(context);
                    break;
            }
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // 注册U盘相关广播接收器
        IntentFilter filter = new IntentFilter();
        filter.addAction(Intent.ACTION_MEDIA_MOUNTED);
        filter.addAction(Intent.ACTION_MEDIA_EJECT);
        filter.addAction(Intent.ACTION_MEDIA_UNMOUNTED);
        filter.addDataScheme("file");
        registerReceiver(mUsbReceiver, filter);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        // 注销U盘相关广播接收器
        unregisterReceiver(mUsbReceiver);
    }

    private String getFactoryApkPath(Context context) {
        String apkPath = null;
        File usbRoot = getUsbRoot(context);
        if (usbRoot != null) {
            File[] files = usbRoot.listFiles(new FilenameFilter() {
                @Override
                public boolean accept(File dir, String name) {
                    return name.equals(FACTORY_APK_NAME);
                }
            });
            if (files != null && files.length > 0) {
                apkPath = files[0].getAbsolutePath();
            }
        }
        return apkPath;
    }

    private File getUsbRoot(Context context) {
        File usbRoot = null;
        StorageManager storageManager = (StorageManager) context.getSystemService(Context.STORAGE_SERVICE);
        try {
            String[] volumePaths = (String[]) storageManager.getClass().getMethod("getVolumePaths").invoke(storageManager);
            for (String path : volumePaths) {
                File file = new File(path);
                if (file.exists() && file.isDirectory() && file.canRead()) {
                    StatFs statFs = new StatFs(file.getAbsolutePath());
                    if (statFs.getBlockCountLong() > 0 && statFs.getBlockSizeLong() > 0 &&
                            statFs.getAvailableBlocksLong() * statFs.getBlockSizeLong() > 0) {
                        usbRoot = file;
                        break;
                    }
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return usbRoot;
    }

    private void startFactoryApk(Context context, String apkPath) {
        if (mIsFactoryApkRunning) {
            return;
        }
        Intent intent = context.getPackageManager().getLaunchIntentForPackage(FACTORY_APK_PACKAGE_NAME);
        if (intent == null) {
            intent = new Intent(Intent.ACTION_VIEW);
            intent.setDataAndType(Uri.fromFile(new File(apkPath)), "application/vnd.android.package-archive");
        }
        intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        context.startActivity(intent);
        mIsFactoryApkRunning = true;
    }

    private void stopFactoryApk(Context context) {
        if (!mIsFactoryApkRunning) {
            return;
        }
        ActivityManager activityManager = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
        List<ActivityManager.RunningAppProcessInfo> processInfoList = activityManager.getRunningAppProcesses();
        for (ActivityManager.RunningAppProcessInfo processInfo : processInfoList) {
            if (processInfo.processName.equals(FACTORY_APK_PACKAGE_NAME)) {
                android.os.Process.killProcess(processInfo.pid);
                break;
            }
        }
        mIsFactoryApkRunning = false;
    }

    private void uninstallUsb(final Context context) {
        if (mIsUninstalling) {
            return;
        }
        mIsUninstalling = true;
        new Thread(new Runnable() {
            @Override
            public void run() {
                while (isFactoryApkRunning(context)) {
                    try {
                        Thread.sleep(WAIT_TIME);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                String path = getUsbRoot(context).getAbsolutePath();
                String cmd = "pm uninstall " + path;
                try {
                    Runtime.getRuntime().exec(cmd);
                } catch (IOException e) {
                    e.printStackTrace();
                }
                mIsUninstalling = false;
            }
        }).start();
    }

    private boolean isFactoryApkRunning(Context context) {
        ActivityManager activityManager = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
        List<ActivityManager.RunningAppProcessInfo> processInfoList = activityManager.getRunningAppProcesses();
        for (ActivityManager.RunningAppProcessInfo processInfo : processInfoList) {
            if (processInfo.processName.equals(FACTORY_APK_PACKAGE_NAME)) {
                return true;
            }
        }
        return false;
    }
}

以上是一个简单的示例代码实现方式，具体实现方式可能会因为需求和环境的不同而有所不同。