问react无法获取restController响应

EN

String fileName = DateUtility.dateToStr(new Date(), DateUtility.YYYYMMDD_HHMMSS) + " - "
            + reportNmaeByType.get(exportParam.getReportType()) + ".xls";
    HttpHeaders headers = new HttpHeaders();
    headers.setContentDispositionFormData("attachment", fileName);
    headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);

    return new ResponseEntity<>(excelByte, HttpStatus.OK);

createExcelFile(){
    var params = {
    reportResultList: this.state.reportResult, 
    reportType: getReportSelector().state.selectedReportType,
    selectColumnMap: this.state.selectColumn,
    selectCusColumnMap: this.state.selectCusColumn
                }
    fetch("http://localhost:8080/mark-web/file/createExcel", {
        method: 'POST',
        headers: {
            'Content-Type': 'application/json',
        },
        body: JSON.stringify(params)
    }).then(res => {
        if (res.ok) {
            console.log(res)
            console.log(this)
             console.log('create excel success!!')
        } else {
            console.log('create excel Fail!!')
        }
    })
}

}).then(res => {
       if(!res.ok){
        console.log("Failed To Download File")
       }else{
        return res.blob()
       }
    }).then(blob => {
        console.log(blob)
        let url = URL.createObjectURL(blob)
        console.log(url)
        var downloadAnchorNode = document.createElement('a')
        downloadAnchorNode.setAttribute("href", url)
        downloadAnchorNode.setAttribute("download", "excel" + ".xls")
        downloadAnchorNode.click()
        downloadAnchorNode.remove()
    })