如何使用android studio在app中读取内部或外部存储(SD卡)中的文件？

<uses-permission android:name="android.permission.READ_INTERNAL_STORAGE" />

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

private static final int REQUEST_PERMISSION = 1;
private static final String[] PERMISSIONS = {
    Manifest.permission.READ_EXTERNAL_STORAGE
};

// 检查权限
private boolean checkPermission() {
    int result = ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE);
    return result == PackageManager.PERMISSION_GRANTED;
}

// 请求权限
private void requestPermission() {
    ActivityCompat.requestPermissions(this, PERMISSIONS, REQUEST_PERMISSION);
}

// 处理权限请求结果
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
    if (requestCode == REQUEST_PERMISSION) {
        if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
            // 权限已授予，可以进行文件读取操作
            readFiles();
        } else {
            // 权限被拒绝，无法进行文件读取操作
            Toast.makeText(this, "权限被拒绝", Toast.LENGTH_SHORT).show();
        }
    }
}

private void readFiles() {
    // 读取内部存储中的文件
    File internalFile = new File(getFilesDir(), "filename.txt");
    // 读取外部存储中的文件
    File externalFile = new File(Environment.getExternalStorageDirectory(), "filename.txt");

    try {
        // 读取文件内容
        BufferedReader reader = new BufferedReader(new FileReader(internalFile));
        String line;
        StringBuilder content = new StringBuilder();
        while ((line = reader.readLine()) != null) {
            content.append(line);
        }
        reader.close();

        // 处理文件内容
        // ...

    } catch (IOException e) {
        e.printStackTrace();
    }
}

File publicDir = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOCUMENTS);
File file = new File(publicDir, "filename.txt");