怎样实现Web组件的下载能力？

 this.delegate.onBeforeDownload((webDownloadItem: webview.WebDownloadItem) => {
              console.log("will start a download.");
              // 传入一个下载路径，并开始下载。
              // 如果传入一个不存在的路径，则会下载到默认/dataorage/el2/base/cache/web/目录。
              webDownloadItem.start("/dataorage/el2/base/cache/web/" + webDownloadItem.getSuggestedFileName());
            })
            this.delegate.onDownloadUpdated((webDownloadItem: webview.WebDownloadItem) => {
              // 下载任务的唯一标识。
              console.log("download update guid: " + webDownloadItem.getGuid());
              // 下载的进度。
              console.log("download update guid: " + webDownloadItem.getPercentComplete());
              // 当前的下载速度。
              console.log("download update speed: " + webDownloadItem.getCurrentSpeed())
            })
            this.delegate.onDownloadFailed((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download failed guid: " + webDownloadItem.getGuid());
              // 下载任务失败的错误码。
              console.log("download failed guid: " + webDownloadItem.getLastErrorCode());
            })
            this.delegate.onDownloadFinish((webDownloadItem: webview.WebDownloadItem) => {
              console.log("download finish guid: " + webDownloadItem.getGuid());
            })
            this.controller.setDownloadDelegate(this.delegate);
          } catch (error) {
            console.error(`ErrorCode: ${(error as BusinessError).code},  Message: ${(error as BusinessError).message}`);
          }