Android 5.1.1在外置SD卡中创建文件夹

Android 4.4之后WRITE_MEDIA_STORAGE 权限仅提供给系统应用，不再授予第三方App，WRITE_EXTERNAL_STORAGE 权限，仅仅用于授权用户写 primary external storage，除了与自己包名相关的文件夹之外，应用程序不允许写secondary external storage devices；

举例来说，如果应用的包名是com.travis.example，那么外部存储上的Android/data/com.travis.example/文件夹就可随意访问，其他任何地方都不允许写，并且，存储在自己包名相关的文件夹的文件，当该应用被卸载时候也会随之被清除。

分以下三种情况：

• 只有外部存储的设备，这种设备一般是android4.0之前的，只有一个存储，不受这个规则限制，还是可以随便读写，但如果高于4.4系统，那么就只能写自己包名相关（上述规则）的文件夹了。

• 只有内部存储的设备，不受这个规则限制，但是建议在自己的包名相关的文件夹写数据。

• 既有内部存储又有外部存储需要遵守这个规定，不可以在外部存储乱写了，需要在自己的包名相关的文件夹写数据。

Google官网原话如此：

The WRITE_EXTERNAL_STORAGE permission must only grant write access to the primary external storage on a device. Apps must not be allowed to write to secondary external storage devices, except in their package-specific directories as allowed by synthesized permissions.Restricting writes in this way ensures the system can clean up fileswhen applications are uninstalled.

先给出创建后的效果日志：

                               

具体的Log日志如下：            

08-15 14:00:53.005 8458-8458/com.flash E/Logger: [ (SdCardUtil.java:98)#main ] 路径:/storage/emulated/0
08-15 14:00:53.006 8458-8458/com.flash E/Logger: [ (SdCardUtil.java:98)#main ] 路径:/storage/uicc0
08-15 14:00:53.006 8458-8458/com.flash E/Logger: [ (SdCardUtil.java:98)#main ] 路径:/storage/sdcard1
08-15 14:00:53.010 8458-8458/com.flash E/Logger: [ (MyApplication.java:39)#main ] 文件路径：/storage/sdcard1/Android/data/com.flash/cache/
08-15 14:00:53.524 8458-8577/com.flash E/Logger: [ (MainActivity.java:234)#Thread-2256 ] /storage/sdcard1/Android/data/com.flash/cache/photos/q
08-15 14:00:53.799 8458-8577/com.flash E/Logger: [ (MainActivity.java:234)#Thread-2256 ] /storage/sdcard1/Android/data/com.flash/cache/photos/u
08-15 14:00:53.956 8458-8577/com.flash E/Logger: [ (MainActivity.java:234)#Thread-2256 ] /storage/sdcard1/Android/data/com.flash/cache/photos/w
08-15 14:00:54.118 8458-8577/com.flash E/Logger: [ (MainActivity.java:234)#Thread-2256 ] /storage/sdcard1/Android/data/com.flash/cache/videos
08-15 14:00:54.230 8458-8577/com.flash E/Logger: [ (MainActivity.java:234)#Thread-2256 ] /storage/sdcard1/Android/data/com.flash/cache/apk
08-15 14:00:54.318 8458-8577/com.flash E/Logger: [ (MainActivity.java:234)#Thread-2256 ] /storage/sdcard1/Android/data/com.flash/cache/shanghai/w
08-15 14:00:54.577 8458-8577/com.flash E/Logger: [ (MainActivity.java:234)#Thread-2256 ] /storage/sdcard1/Android/data/com.flash/cache/images

很明显，属于第三种情况，存在外部存储，也存在内部存储的情况，因此在外置SD卡中创建文件夹的时候，需要按照Google官方给出的规则来创建，即为：外部路径 + Android + data + 包名 + cache / file + 需要创建的文件夹名称；

具体代码如下：

   /**
     * 获取外置SD卡路径
     */
    public static List<String> getExtSDCardPathList() {
        List<String> paths = new ArrayList<String>();
        String extFileStatus = Environment.getExternalStorageState();
        File extFile = Environment.getExternalStorageDirectory();
        //首先判断一下外置SD卡的状态，处于挂载状态才能获取的到
        if (extFileStatus.equals(Environment.MEDIA_MOUNTED) && extFile.exists() && extFile.isDirectory() && extFile.canWrite()) {
            //外置SD卡的路径
            paths.add(extFile.getAbsolutePath());
        }
        try {
            Runtime runtime = Runtime.getRuntime();
            Process process = runtime.exec("mount");
            InputStream is = process.getInputStream();
            InputStreamReader isr = new InputStreamReader(is);
            BufferedReader br = new BufferedReader(isr);
            String line = null;
            int mountPathIndex = 1;
            while ((line = br.readLine()) != null) {
                // format of sdcard file system: vfat/fuse
                if ((!line.contains("fat") && !line.contains("fuse") && !line
                        .contains("storage"))
                        || line.contains("secure")
                        || line.contains("asec")
                        || line.contains("firmware")
                        || line.contains("shell")
                        || line.contains("obb")
                        || line.contains("legacy") || line.contains("data")) {
                    continue;
                }
                String[] parts = line.split(" ");
                int length = parts.length;
                if (mountPathIndex >= length) {
                    continue;
                }
                String mountPath = parts[mountPathIndex];
                if (!mountPath.contains("/") || mountPath.contains("data")
                        || mountPath.contains("Data")) {
                    continue;
                }
                File mountRoot = new File(mountPath);
                if (!mountRoot.exists() || !mountRoot.isDirectory()
                        || !mountRoot.canWrite()) {
                    continue;
                }
                boolean equalsToPrimarySD = mountPath.equals(extFile
                        .getAbsolutePath());
                if (equalsToPrimarySD) {
                    continue;
                }
                //扩展存储卡即TF卡或者SD卡路径
                paths.add(mountPath);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return paths;
    }


    public static String getTFSDCardPath() {
        List<String> list;
        list = getExtSDCardPathList();
        return list.get(list.size() - 1);
    }


    /**
     * 获取外置SD卡存储文件的绝对路径
     * Android 4.4以后
     * @param context
     */
    public static String getExternalFileDir(Context context) {
        StringBuilder sb = new StringBuilder();
        File file = context.getExternalCacheDir();     //此句代码一定要，在内部存储空间创建对应的data目录，但不存储文件
        if (file.exists()) {
            sb.append(SdCardUtil.getTFSDCardPath().toString()).append("/Android/data/").append(context.getPackageName())
                    .append("/cache").append(File.separator).toString();
        } else {
            sb.append(SdCardUtil.getTFSDCardPath().toString()).append("/Android/data/").append(context.getPackageName())
                    .append("/cache").append(File.separator).toString();
        }
        return sb.toString();
    }

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