保存文件所需的Android权限是WRITE_EXTERNAL_STORAGE。

以下是一个保存文件的代码示例：

import android.Manifest;
import android.content.Context;
import android.content.pm.PackageManager;
import android.os.Build;
import android.os.Environment;
import android.widget.Toast;

import androidx.core.app.ActivityCompat;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;

public class FileUtil {
    private static final int REQUEST_PERMISSION_CODE = 200;

    public static void saveFile(Context context, String fileName, String content) {
        if (hasWritePermission(context)) {
            saveInternalFile(context, fileName, content);
        } else {
            requestWritePermission(context, fileName, content);
        }
    }

    private static boolean hasWritePermission(Context context) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            return ActivityCompat.checkSelfPermission(context, Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED;
        } else {
            return true;
        }
    }

    private static void requestWritePermission(Context context, String fileName, String content) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            ActivityCompat.requestPermissions((Activity) context, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, REQUEST_PERMISSION_CODE);
        }
    }

    public static void onRequestPermissionsResult(Context context, int requestCode, String[] permissions, int[] grantResults, String fileName, String content) {
        if (requestCode == REQUEST_PERMISSION_CODE) {
            if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                saveInternalFile(context, fileName, content);
            } else {
                Toast.makeText(context, "保存文件需要存储权限", Toast.LENGTH_SHORT).show();
            }
        }
    }

    private static void saveInternalFile(Context context, String fileName, String content) {
        File file = new File(Environment.getExternalStorageDirectory(), fileName);
        try {
            FileOutputStream fos = new FileOutputStream(file);
            fos.write(content.getBytes());
            fos.close();
            Toast.makeText(context, "文件保存成功", Toast.LENGTH_SHORT).show();
        } catch (IOException e) {
            e.printStackTrace();
            Toast.makeText(context, "文件保存失败", Toast.LENGTH_SHORT).show();
        }
    }
}

在Activity或Fragment中，调用FileUtil.saveFile()方法保存文件。

String fileName = "example.txt";
String content = "Hello, world!";
FileUtil.saveFile(this, fileName, content);

为了正常运行，还需要在AndroidManifest.xml文件中添加以下权限：