MockMultipartFile exists for this purpose. As in your snippet if the file path is known, the below code works for me.

import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import org.springframework.mock.web.MockMultipartFile;

Path path = Paths.get("/path/to/the/file.txt");
String name = "file.txt";
String originalFileName = "file.txt";
String contentType = "text/plain";
byte[] content = null;
try {
    content = Files.readAllBytes(path);
} catch (final IOException e) {
}
MultipartFile result = new MockMultipartFile(name,
                     originalFileName, contentType, content);

You can get the content of a MultipartFile by using the getBytes method and you can write to the file using Files.newOutputStream():

public void write(MultipartFile file, Path dir) {
    Path filepath = Paths.get(dir.toString(), file.getOriginalFilename());

    try (OutputStream os = Files.newOutputStream(filepath)) {
        os.write(file.getBytes());
    }
}

You can also use the transferTo method:

public void multipartFileToFile(
    MultipartFile multipart, 
    Path dir
) throws IOException {
    Path filepath = Paths.get(dir.toString(), multipart.getOriginalFilename());
    multipart.transferTo(filepath);
}

    File file = new File("src/test/resources/input.txt");
    FileInputStream input = new FileInputStream(file);
    MultipartFile multipartFile = new MockMultipartFile("file",
            file.getName(), "text/plain", IOUtils.toByteArray(input));

This is another way of getting multipart file from File object

InputStream stream =  new FileInputStream(file)
multipartFileToSend = new MockMultipartFile("file", file.getName(), MediaType.TEXT_HTML_VALUE, stream);

try this

If you upload like that then file will read from local and it will not read when u check-in or run from server.

Use common Multipart or standard Multipart resolver which may solve your issue.

Refer below code.

JSP
method="POST" enctype="multipart/form-data">

Controller:

Multipart upload;
byte[] bytes = file.getBytes(); 
Path path=file.get(fileinputstream (upload));

Bean:

private Multipart upload;
Getter and setter method;

Register Bean

@Bean public MultipartResolver multipartResolver() { 
    return new StandardServletMultipartResolver(); 
}