How to send the Multipart file and json data to spring boot

You cat use @RequestParam and Converter for JSON objects
simple example :

@SpringBootApplication
public class ExampleApplication {

    public static void main(String[] args) {
        SpringApplication.run(ExampleApplication.class, args);
    }

    @Data
    public static class User {
        private String name;
        private String lastName;
    }

    @Component
    public static class StringToUserConverter implements Converter<String, User> {

        @Autowired
        private ObjectMapper objectMapper;

        @Override
        @SneakyThrows
        public User convert(String source) {
            return objectMapper.readValue(source, User.class);
        }
    }

    @RestController
    public static class MyController {

        @PostMapping("/upload")
        public String upload(@RequestParam("file") MultipartFile file, 
                             @RequestParam("user") User user) {
            return user + "\n" + file.getOriginalFilename() + "\n" + file.getSize();
        }

    }

}

and postman:

UPDATE apache httpclient 4.5.6 example:

pom.xml dependency:

    <dependency>
        <groupId>org.apache.httpcomponents</groupId>
        <artifactId>httpclient</artifactId>
        <version>4.5.6</version>
    </dependency>
    <dependency>
        <groupId>org.apache.httpcomponents</groupId>
        <artifactId>httpmime</artifactId>
        <version>4.5.6</version>
    </dependency>

   <!--dependency for IO utils-->
    <dependency>
        <groupId>commons-io</groupId>
        <artifactId>commons-io</artifactId>
        <version>2.6</version>
    </dependency>

service will be run after application fully startup, change File path for your file

@Service
public class ApacheHttpClientExample implements ApplicationRunner {

    private final ObjectMapper mapper;

    public ApacheHttpClientExample(ObjectMapper mapper) {
        this.mapper = mapper;
    }

    @Override
    public void run(ApplicationArguments args) {
        try (CloseableHttpClient client = HttpClientBuilder.create().build()) {
            File file = new File("yourFilePath/src/main/resources/foo.json");
            HttpPost httpPost = new HttpPost("http://localhost:8080/upload");

            ExampleApplication.User user = new ExampleApplication.User();
            user.setName("foo");
            user.setLastName("bar");
            StringBody userBody = new StringBody(mapper.writeValueAsString(user), MULTIPART_FORM_DATA);
            FileBody fileBody = new FileBody(file, DEFAULT_BINARY);

            MultipartEntityBuilder entityBuilder = MultipartEntityBuilder.create();
            entityBuilder.addPart("user", userBody);
            entityBuilder.addPart("file", fileBody);
            HttpEntity entity = entityBuilder.build();
            httpPost.setEntity(entity);

            HttpResponse response = client.execute(httpPost);
            HttpEntity responseEntity = response.getEntity();

            // print response
            System.out.println(IOUtils.toString(responseEntity.getContent(), UTF_8));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

console output will look like below:

ExampleApplication.User(name=foo, lastName=bar)
foo.json
41

You can use both of them.

@RequestPart : This annotation associates a part of a multipart request with the method argument, which is useful for sending complex multi-attribute data as payload, e.g., JSON or XML.

In other words Request Part parse your json string object from request to your class object. On the other hand, Request Param just obtain the string value from your json string value.

For example, using Request Part:

@RestController
@CrossOrigin(origins = "*", methods= {RequestMethod.POST, RequestMethod.GET,
RequestMethod.PUT})
@RequestMapping("/api/api-example")
public class ExampleController{    
@PostMapping("/endpoint-example")
public ResponseEntity<Object> methodExample(
    @RequestPart("test_file") MultipartFile file,
    @RequestPart("test_json") ClassExample class_example) { 
      /* do something */ 
 }
}

and postman would be configured like:

@RequestParam : Another way of sending multipart data is to use @RequestParam. This is especially useful for simple data, which is sent as key/value pairs along with the file, as I said, just key/value. Also is used to get value from query params, I think that is its main goal.