`package com.example.attendingsystembackend.model;
import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.Id;
import jakarta.persistence.Lob;
import jakarta.validation.constraints.NotBlank;
import jakarta.validation.constraints.NotNull;
import org.hibernate.annotations.GenericGenerator;
import java.time.LocalDateTime;
@Entity
public class Event {
    @Id
    @GeneratedValue(generator = "system-uuid")
    @GenericGenerator(name="system-uuid",strategy = "uuid")
    private String id;
    @NotBlank(message = "Event name cannot be blank")
    private String eventName;
    private String eventType;
    @NotBlank(message = "Event location cannot be blank")
    private String location;
    @NotNull
    private LocalDateTime startTime;
    @NotNull
    private LocalDateTime endTime;
    @Lob
    private byte[] eventFlyer;
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public String getEventName() {
        return eventName;
    }
    public void setEventName(String eventName) {
        this.eventName = eventName;
    }
    public String getEventType() {
        return eventType;
    }
    public void setEventType(String eventType) {
        this.eventType = eventType;
    }
    public String getLocation() {
        return location;
    }
    public void setLocation(String location) {
        this.location = location;
    }
    public LocalDateTime getStartTime() {
        return startTime;
    }
    public void setStartTime(LocalDateTime startTime) {
        this.startTime = startTime;
    }
    public LocalDateTime getEndTime() {
        return endTime;
    }
    public void setEndTime(LocalDateTime endTime) {
        this.endTime = endTime;
    }
    public byte[] getEventFlyer() {
        return eventFlyer;
    }
    public void setEventFlyer(byte[] eventFlyer) {
        this.eventFlyer = eventFlyer;
    }
}`

package com.example.attendingsystembackend.service;
import com.example.attendingsystembackend.model.Event;
import com.example.attendingsystembackend.repository.EventRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.web.multipart.MultipartFile;
import java.io.IOException;
@Service
public class EventService {
    private final EventRepository eventRepository;
    @Autowired
    public EventService(EventRepository eventRepository) {
        this.eventRepository = eventRepository;
    }
    public void saveEvent(MultipartFile file, Event event) throws IOException {
        Event newEvent=new Event();
        newEvent.setEventName(event.getEventName());
        newEvent.setEventType(event.getEventType());
        newEvent.setLocation(event.getLocation());
        newEvent.setStartTime(event.getStartTime());
        newEvent.setEndTime(event.getEndTime());
        if(file!=null && !file.isEmpty()) {
            byte[] fileBytes = file.getBytes();
            newEvent.setEventFlyer(fileBytes);
        }else{
            newEvent.setEventFlyer(null);
        }
        eventRepository.save(newEvent);
    }
    }

package com.example.attendingsystembackend.controller;
import com.example.attendingsystembackend.model.Event;
import com.example.attendingsystembackend.service.EventService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.multipart.MultipartFile;
@RestController
@RequestMapping("api/event")
public class EventController {
    private final EventService eventService;
    @Autowired
    public EventController(EventService eventService) {
        this.eventService = eventService;
    }
    @PostMapping(value="saveEvent")
    public ResponseEntity<String> saveEvent(@RequestParam(value = "file", required = false) MultipartFile file, Event event) {
        try {
            eventService.saveEvent(file,event);
            return ResponseEntity.status(HttpStatus.OK)
                    .body(String.format("Event saved succesfully with file: %s", file.getOriginalFilename()));
        } catch (Exception e) {
            return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR)
                    .body(String.format("Could not save the event: %s!", e));
        }
    }
}

Validation failed for argument [1] in public org.springframework.http.ResponseEntity<java.lang.String> com.example.attendingsystembackend.controller.EventController.saveEvent(org.springframework.web.multipart.MultipartFile,com.example.attendingsystembackend.model.Event): [Field error in object 'event' on field 'eventFlyer': rejected value [org.springframework.web.multipart.support.StandardMultipartHttpServletRequest$StandardMultipartFile@42f6b750]; codes [typeMismatch.event.eventFlyer,typeMismatch.eventFlyer,typeMismatch.[B,typeMismatch]; arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [event.eventFlyer,eventFlyer]; arguments []; default message [eventFlyer]]; default message [Failed to convert property value of type 'org.springframework.web.multipart.support.StandardMultipartHttpServletRequest$StandardMultipartFile' to required type 'byte[]' for property 'eventFlyer'; Cannot convert value of type 'org.springframework.web.multipart.support.StandardMultipartHttpServletRequest$StandardMultipartFile' to required type 'byte' for property 'eventFlyer[0]': PropertyEditor [org.springframework.beans.propertyeditors.CustomNumberEditor] returned inappropriate value of type 'org.springframework.web.multipart.support.StandardMultipartHttpServletRequest$StandardMultipartFile']] ]

@PostMapping(value="saveEvent")
public ResponseEntity<String> saveEvent(@RequestPart("file") MultipartFile file, @RequestPart("body") Event event) // you can also pass json as string value and then map into objects