HarmonyOS 鸿蒙Next 下载pdf文件并保存到用户文件目录

可以参考下demo

import { BusinessError, request } from '[@kit](/user/kit).BasicServicesKit';
import picker from '[@ohos](/user/ohos).file.picker';
import fs from '[@ohos](/user/ohos).file.fs';
import { common } from '[@kit](/user/kit).AbilityKit';
import { buffer } from '[@kit](/user/kit).ArkTS';
[@Entry](/user/Entry)
[@Component](/user/Component)
struct DocumentSave {
 [@State](/user/State) message: string = '下载文件';
 build() {
   RelativeContainer() {
     Text(this.message)
       .id('DocumentSaveHelloWorld')
       .fontSize(50)
       .fontWeight(FontWeight.Bold)
       .fontColor(Color.Pink)
       .alignRules({
         center: { anchor: '__container__', align: VerticalAlign.Center },
         middle: { anchor: '__container__', align: HorizontalAlign.Center }
       })
       .onClick(()=>{
         const context = getContext(this);
         const downloadUrl = '文件链接名.pdf';
         try {
           request.downloadFile(context, {
             enableMetered: true,
             url: downloadUrl,
             filePath: context.filesDir + '/aa.pdf'
           }).then((downloadTask: request.DownloadTask) => {
             downloadTask.on('fail', (err: number) => {
               console.error(`Failed to download the task. Code: ${err}`);
             });
             downloadTask.on('progress', (receivedSize: number, totalSize: number) => {
               console.log('download', "receivedSize:" + (receivedSize / 1024) + " totalSize:" + (totalSize / 1024));
             });
             downloadTask.on('complete', () => {
               //将文件复制到文件夹中
               const documentSaveOptions = new picker.DocumentSaveOptions(); // 创建文件管理器保存选项实例
               documentSaveOptions.newFileNames = ["aaa.pdf"]; // 保存文件名（可选）
               const documentViewPicker = new picker.DocumentViewPicker;
               documentViewPicker.save(documentSaveOptions)
                 .then(async (documentSaveResult) => {
                   // 获取到到图片或者视频文件的URI后进行文件读取等操作
                   let uri = documentSaveResult[0];
                   console.info('pub uri:' + uri)
                   // 沙箱路径文件
                   let sanFile = fs.openSync(context.filesDir+ '/aa.pdf', fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE)
                   let pubFile = fs.openSync(uri, fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE)
                   // 将文件从沙箱路拷贝到公共路径
                   fs.copyFileSync(sanFile.fd, pubFile.fd)
                   console.log("-------")
                 })
               console.log('下载完成')
             })}
             // 下载完成
           )
             .catch((err: BusinessError) => {
               console.error(`Invoke downloadTask failed, code is ${err.code}, message is ${err.message}`);
             });
         } catch (error) {
           let err: BusinessError = error as BusinessError;
           console.error(`Invoke downloadFile failed, code is ${err.code}, message is ${err.message}`);
         }
       })
   }
   .height('100%')
   .width('100%')
 }
}