Here we will create a rest APi which will take file object as a multipart parameter from front end and upload it to S3 bucket using java rest API.

Requirement :- secrete key and Access key for s3 bucket where you wanna upload your file.

code:- DocumentController.java

@RestController
@RequestMapping("/api/v2")
public class DocumentController {

    private static String bucketName = "pharmerz-chat";
    //   private static String keyName        = "Pharmerz"+ UUID.randomUUID();

    @RequestMapping(value = "/upload", method = RequestMethod.POST, consumes = MediaType.MULTIPART_FORM_DATA)
    public URL uploadFileHandler(@RequestParam("name") String name,
                                 @RequestParam("file") MultipartFile file) throws IOException {

/******* Printing all the possible parameter from @RequestParam *************/

        System.out.println("*****************************");

        System.out.println("file.getOriginalFilename() " + file.getOriginalFilename());
        System.out.println("file.getContentType()" + file.getContentType());
        System.out.println("file.getInputStream() " + file.getInputStream());
        System.out.println("file.toString() " + file.toString());
        System.out.println("file.getSize() " + file.getSize());
        System.out.println("name " + name);
        System.out.println("file.getBytes() " + file.getBytes());
        System.out.println("file.hashCode() " + file.hashCode());
        System.out.println("file.getClass() " + file.getClass());
        System.out.println("file.isEmpty() " + file.isEmpty());

        /*************Parameters to b pass to s3 bucket put Object **************/
        InputStream is = file.getInputStream();
        String keyName = file.getOriginalFilename();


// Credentials for Aws  
        AWSCredentials credentials = new BasicAWSCredentials("AKIA*************", "zr**********************");

        /****************** DocumentController.uploadfile(credentials); ***************************/


        AmazonS3 s3client = new AmazonS3Client(credentials);
        try {
            System.out.println("Uploading a new object to S3 from a file\n");
            //File file = new File(awsuploadfile);
            s3client.putObject(new PutObjectRequest(
                    bucketName, keyName, is, new ObjectMetadata()));


            URL url = s3client.generatePresignedUrl(bucketName, keyName, Date.from(Instant.now().plus(5, ChronoUnit.MINUTES)));
            // URL url=s3client.generatePresignedUrl(bucketName,keyName, Date.from(Instant.now().plus(5, ChronoUnit.)));
            System.out.println("************************************");
            System.out.println(url);

            return url;

        } catch (AmazonServiceException ase) {
            System.out.println("Caught an AmazonServiceException, which " +
                    "means your request made it " +
                    "to Amazon S3, but was rejected with an error response" +
                    " for some reason.");
            System.out.println("Error Message:    " + ase.getMessage());
            System.out.println("HTTP Status Code: " + ase.getStatusCode());
            System.out.println("AWS Error Code:   " + ase.getErrorCode());
            System.out.println("Error Type:       " + ase.getErrorType());
            System.out.println("Request ID:       " + ase.getRequestId());
        } catch (AmazonClientException ace) {
            System.out.println("Caught an AmazonClientException, which " +
                    "means the client encountered " +
                    "an internal error while trying to " +
                    "communicate with S3, " +
                    "such as not being able to access the network.");
            System.out.println("Error Message: " + ace.getMessage());
        }

        return null;

    }


}

Front end Function

var form = new FormData();
form.append("file", "image.jpeg");

var settings = {
 "async": true,
 "crossDomain": true,
 "url": "http://url/",
 "method": "POST",
 "headers": {
   "cache-control": "no-cache"
 },
 "processData": false,
 "contentType": false,
 "mimeType": "multipart/form-data",
 "data": form
}

$.ajax(settings).done(function (response) {
 console.log(response);
});