How can I save the report as a Multipart file.

I'm using angular and spring boot. And I want to save the report in server. So I tried MultipartFile in the spring boot controller to store request params and file is not saving. So is there any better way to do it? or is there any default format for RequestParms?
 
 
 
Here is my code
.ts file
 
function reportSaveHandler() {
            pivot.save({
                filename: 'myreport.json',
                destination: 'server',
                url: 'http://localhost:8082/reports/uploadFile',
                requestHeaders:{
                    'Authorization':'Bearer '+token,
                }
            });
        }
 
.java File (controller)
 
public class ReportsController {
@RequestMapping(method = RequestMethod.POST,value = "/uploadFile")
public void uploadReports(MultipartFile file) {
System.out.println(file.toString());
}
}
 
 
I'm getting nullpointerException while printing.