manifest.xml加权限：

python
<uses-permission
        android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"
        tools:ignore="ProtectedPermissions" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE" />

oncreate加代码能向用户获取权限：

python
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, 1);
        }
        //申请写权限
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, 1);
        }
        //申请创建文件
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.MANAGE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.MANAGE_EXTERNAL_STORAGE}, 1);
        }

加一个方法：

python
public static void createFileRecursion(String fileName, Integer height) throws IOException {
        Path path = Paths.get(fileName);
        if (Files.exists(path)) {
            return;
        }
        if (Files.exists(path.getParent())) {
            if (height == 0) {
                Files.createFile(path);
            } else {
                Files.createDirectory(path);
            }
        } else {
            createFileRecursion(path.getParent().toString(), height + 1);
            createFileRecursion(fileName, height);
        }
    }

实现写入：

python
                        try {
                            String jsonPath="/sdcard/Download/1.json";
                            createFileRecursion(jsonPath, 0);
                            FileWriter fileWriter = new FileWriter(jsonPath);
                            fileWriter.write(String.valueOf(msg.obj));
                            fileWriter.flush();
                            fileWriter.close();
                            Log.i("JSON_WRITE", "jsonPath: " + jsonPath);
                        } catch (IOException e) {
                            e.printStackTrace();
                        }