HarmonyOS 鸿蒙Next 如何将下载的图片缓存到沙盒里面，以便重复使用

HarmonyOS 鸿蒙Next 如何将下载的图片缓存到沙盒里面，以便重复使用

下面我写的代码中意图，将下载的文件写入filePath，然后当第二次来下载时，我会去先判断是否存在缓存文件。
现在遇到的问题是，第一次下载成功并写入到filePath中，第二次判断也存在此filePath，但是无法正常显示filePath的数据。
所以这里因该是我的缓存写错了，想请教指正一下。

///下载任务
static downloadWithFile(context:common.UIAbilityContext,params:DownloadParams,callback:(code:number,msg:string,path:string)=>void,progress?:(receivedSize:number,totalSize:number)=>void){
const filePathSuffix = DownloadUtil.guessFileName(params.url)
const filePath = context.filesDir + "/" + filePathSuffix
const uri = fileUri.getUriFromPath(filePath);
try {
const isExit = fileIo.accessSync(filePath,fileIo.OpenMode.READ_WRITE)
if(isExit){
LogUtil.info(`${DownloadUtil.TAG} downalod file is Already success, do not need downalod again`);
callback(0,"已下载成功",uri)
return
}
request.downloadFile(context, {
header:params.headers,
url: params.url,
filePath: filePath,
title:params.title,
description:params.description,
enableMetered:true

}, (err: BusinessError, data: request.DownloadTask) => {
///错误码文档：https://developer.huawei.com/consumer/cn/doc/harmonyos-references-V5/js-apis-request-V5#%E4%B8%8B%E8%BD%BD%E4%BB%BB%E5%8A%A1%E7%9A%84%E9%94%99%E8%AF%AF%E7%A0%81
///https://developer.huawei.com/consumer/cn/doc/harmonyos-references-V5/errorcode-request-V5#section13400002-%E6%96%87%E4%BB%B6%E8%B7%AF%E5%BE%84%E5%BC%82%E5%B8%B8
if (err) {
callback(err.code,err.message,uri)
LogUtil.error(`${DownloadUtil.TAG} Failed to request the download. Code: ${err.code}, message: ${err.message}`);
return;
}
let downloadTask: request.DownloadTask = data;

///下载失败的回调
let failCallback = (code: number) => {
const msg = DownloadUtil.getFailCallbackMsgByCode(code)
LogUtil.error(`${DownloadUtil.TAG} Failed to download the task. Code: ${code}`);
///取消进度监听
downloadTask.off('progress');
callback(code,msg,uri)
};
downloadTask.on('fail', failCallback);

///下载完毕的回调
let completeCallback = () => {
let file = fileIo.openSync(filePath, fileIo.OpenMode.READ_WRITE);
fileIo.closeSync(file);
LogUtil.info(`${DownloadUtil.TAG} request the download complete data:${data}}`);
///取消进度监听
downloadTask.off('progress');
callback(HttpConstant.HTTP_SUCCESS,"下载完成",uri)
};
downloadTask.on('complete', completeCallback);

if(progress){
///下载进度的回调
let progressCallback = (receivedSize:number,totalSize:number) => {
progress(receivedSize,totalSize)
};
downloadTask.on('progress', progressCallback);
}
});
} catch (error) {
let err = error as BusinessError
let code = HttpConstant.HTTP_FAULT_DOWNLOAD
if(err.code && err.code != 0){
code = err.code
}
callback(code,JSON.stringify(err),uri)
}
}