HarmonyOS 鸿蒙Next 从本地下载json文件存入沙箱后读取出来使用json解析报错，但json.cn在线解析正常

可以看一下class-transformer三方库，可以实现string转成对象：

可以参考这个demo：

import request from '@ohos.request';

import picker from '@ohos.file.picker';

import fs, { ReadOptions } from '@ohos.file.fs';

import common from '@ohos.app.ability.common';

import { buffer } from '@kit.ArkTS';

import  { plainToClass } from "class-transformer";

// 获取应用文件路径

let context = getContext(this) ;

let message = ''

function down(context: Context, url: string, fileName: string, outFilePath: string, isJson:boolean) {

  let filesDir = context.filesDir;

  let filePath = filesDir + fileName

  request.downloadFile(context, {

    url: url,

    filePath: filePath,

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

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

      console.info('download complete fileName ： ' + fileName)

      // fs.copyFileSync(filePath, outFilePath)

      //读取

      if(isJson){

        let result =readFileContent(context, fileName)

        console.log(result);

        message =result

      }else{

        console.log('1');

      }

    })

    downloadTask.on('progress', (uploadedSize: number, totalSize: number) => {

      console.info('progress >> ' + 'uploadedSize : ' + uploadedSize + ' ; totalSize :' + totalSize)

    })

    downloadTask.on('fail', (err: number) => {

      console.info('download fail >> ' + 'err : ' + err)

    })

  })

}

export class CoursePlayStepBean {

  ratings: Ratings[] = []

  steps: Steps[] = []

  branchs: BranchStep[] = []

  videoCall: string = ''

}

export class BranchStep {

  id: string = ''

  name: string = ''

  image: string = ''

  liveUrl: string = ''

  steps: Steps[] = []

}

export class Steps {

  scene: string = ''

  scale: string = ''

  audio: string = ''

  video: string = ''

  image: string = ''

  branch: number = 0

  tag: string = ''

}

export class Ratings {

  lottie: string = ''

  sounds: string[] = []

  star: number = 0

  bgcolor: Bgcolor = new Bgcolor()

}

export class Bgcolor {

  color: string = ''

  opacity: number = 0

  fade_time: number = 0

}

function readFileContent(context: Context, fileName: string):string{

  let filesDir:string = context.filesDir;

  let filePath = filesDir + fileName

  let file:fs.File = fs.openSync(filePath, fs.OpenMode.READ_WRITE);

  let readSize = 0

  let arrayBuffer = new ArrayBuffer(4096);

  let readAll = 0

  while(true){

    let currSize = fs.readSync(file.fd, arrayBuffer, {offset:readSize, length:4096} )

    if(currSize < 4096){

      break

    }

    readAll += currSize

  }

  fs.closeSync(file);

  let result = buffer.from(arrayBuffer).toString('utf-8')

  console.info('readResult : ' + result)

  return result

}

@Entry

@Component

struct Index4 {

  @State message:string ='test'

  @State coursePlayStepBean:CoursePlayStepBean|undefined = undefined

  build() {

    Column(){

      Button('test').onClick((event: ClickEvent) => {

        down(context,'json','content.json','',true)

      })

      Text(this.message)

        .onClick(()=>{

          this.message = message

          try {

            this.coursePlayStepBean = plainToClass(CoursePlayStepBean, message)

          }

          catch (Error){

          }

          console.log('testsuccess'+JSON.stringify(this.coursePlayStepBean))

        })

    }

  }

}