HarmonyOS 鸿蒙Next 文件下载到哪个目录下才不会被清除？

参考以下代码：

import common from '[@ohos](/user/ohos).app.ability.common';

import fs from '[@ohos](/user/ohos).file.fs';

import request from '[@ohos](/user/ohos).request';

import { BusinessError } from '[@ohos](/user/ohos).base';

import buffer from '[@ohos](/user/ohos).buffer';

import { picker } from '[@kit](/user/kit).CoreFileKit';

[@Entry](/user/Entry)

[@Component](/user/Component)

struct Index {

 build() {

   Button().onClick(() => {

     let context = getContext(this) as common.UIAbilityContext;

     let filePath = context.filesDir + "/test.xlsx";

     let url = "xxx.xlsx"

     try {

       request.downloadFile(context, {

         url: url,

         filePath: filePath

       }).then((data: request.DownloadTask) => {

         let downloadTask: request.DownloadTask = data;

         downloadTask.on('complete', () => {

           console.info('download complete');

           let file = fs.openSync(filePath, fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE);

           let arrayBuffer = new ArrayBuffer(4096000);

           let readLen = fs.readSync(file.fd, arrayBuffer);

           let buf = buffer.from(arrayBuffer, 0, readLen);

           console.info(`content of File: ${buf.toString()}`);

           let writeLen = fs.writeSync(file.fd, arrayBuffer);

           fs.closeSync(file);

           const documentSaveOptions = new picker.DocumentSaveOptions(); // 创建文件管理器选项实例

           // documentSaveOptions.newFileNames = ["1.xlsx"]; // 保存文件名（可选）

           // documentSaveOptions.fileSuffixChoices = ['xlsx']; // 保存文件类型（可选）

           let uris: Array<string> = [];

           const documentViewPicker = new picker.DocumentViewPicker(); // 创建文件选择器实例

           documentViewPicker.save(documentSaveOptions).then((documentSaveResult: Array<string>) => {

             uris = documentSaveResult;

             console.info('documentViewPicker.save to file succeed and uris are:' + uris);

             let uri = uris[0];

             let file2 = fs.openSync(uri, fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE);

             let writeLen2 = fs.writeSync(file2.fd, arrayBuffer);

             fs.closeSync(file2);

           }).catch((err: BusinessError) => {

             console.error(`Invoke documentViewPicker.save failed, code is ${err.code}, message is ${err.message}`);

           })

         })

         let failCallback = () => {

           console.info('Download task fail.');

         };

         downloadTask.on('fail', failCallback);

       }).catch((err: BusinessError) => {

         console.error(`downLoadFileTask failed, code is ${err.code}, message is ${err.message}`);

       });

     } catch (error) {

       console.error(`downLoadFileTask failed, code is ${error.code}, message is ${error.message}`);

     }

   })

 }

}