如何获取系统时间戳以及格式的转换

import systemDateTime from '@ohos.systemDateTime'; 
import { BusinessError } from '@ohos.base'; 
import promptAction from '@ohos.promptAction' 
import image from '@ohos.multimedia.image'; 
 
@Entry 
@Component 
struct Index5 { 
  @State timeStr: string = ''; 
 
  build() { 
    Flex( 
      { direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) { 
      Text(`当前时间：` + this.timeStr) 
        .fontSize(20) 
        .fontWeight(FontWeight.Bold) 
      Button("get time") 
        .width(100) 
        .height(100).onClick(() => { 
        //同步方法获取系统时间戳 
        try { 
          let time = systemDateTime.getTime(false) 
          this.timeStr = this.getTimeToYYYYDDMMHHMMSS(time) 
        } catch (e) { 
          let error = e as BusinessError; 
          console.info(`Failed to get time. message: ${error.message}, code: ${error.code}`); 
        } 
        //异步方法获取系统时间戳 
        try { 
          systemDateTime.getCurrentTime(false, (error, time) => { 
            if (error) { 
              console.info(`Failed to get currentTime. message: ${error.message}, code: ${error.code}`) 
              return; 
            } 
            console.info(`Succeeded in getting currentTime : ${time}`); 
            this.timeStr = this.getTimeToYYYYDDMMHHMMSS(time) 
          }) 
          AlertDialog.show({ message: 'sss' }); 
        } catch (e) { 
          console.info(`Failed to get currentTime. message: ${e.message}, code: ${e.code}`); 
        } 
      }) 
    } 
    .width('100%') 
    .height('100%') 
  } 
 
  //将时间戳转换成日期格式 
  getTimeToYYYYDDMMHHMMSS(str: number): string { 
    let time: string = ""; 
    console.log(str.toString()) 
    let date = new Date(str); 
    console.log(JSON.stringify(date)) 
    try { 
      let year = date.getFullYear(); 
      let month = (date.getMonth() + 1) < 10 ? "0" + (date.getMonth() + 1) : (date.getMonth() + 1); 
      let day = date.getDate() < 10 ? "0" + date.getDate() : date.getDate(); 
      let hour = date.getHours() < 10 ? "0" + date.getHours() : date.getHours(); 
      let min = date.getMinutes() < 10 ? "0" + date.getMinutes() : date.getMinutes(); 
      let second = date.getSeconds() < 10 ? "0" + date.getSeconds() : date.getSeconds(); 
      time = year + "-" + month + "-" + day + " " + hour + ":" + min + ":" + second; 
      console.log(date + "转换===>" + time); 
    } catch (e) { 
      console.info(`Failed to get currentTime. message: ${e.message}, code: ${e.code}`); 
    } 
    return time; 
  } 
}