How to Pass Data from Angular 10 form to Spring Boot Rest API that includes both Strings and Files/Images?

Question

I am getting the following error in Eclipse Console when trying to communicate between Angular 10 and Spring-Boot rest Api.

2020-10-06 23:44:12.261  WARN 33762 --- [nio-8090-exec-5] .w.s.m.s.DefaultHandlerExceptionResolver : Resolved [org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Cannot deserialize instance of `java.lang.String` out of START_OBJECT token; nested exception is com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `java.lang.String` out of START_OBJECT token
 at [Source: (PushbackInputStream); line: 1, column: 535] (through reference chain: com.P.models.PModels["pProfilePic"])]

This is part of my Angular Form

<form class="" action="" method="POST" enctype = "multipart/form-data" role="form" [formGroup]="form" (ngSubmit)="onSubmit()">

                  <input id="name" class="form-control" type="text" placeholder="Your Name" formControlName="pName"
                    class="form-control" [ngClass]="{ 'is-invalid': submitted && f.pName.errors }">
                  <div *ngIf="submitted || f.pName.invalid && (f.pName.dirty || f.pName.touched)"
                    class="alert alert-danger">
                    <div *ngIf="f.pName.errors?.required">Name is required</div>
                  </div>

<div class="form-group row mb-4">
            <label for="uploadPhoto" class="col-md-3 col-form-label">Upload Photo </label>
            <div class="col-md-8">
              <input type="text" class="form-control mb-2 transparent-disabled" id="uploadPhoto"
                placeholder="JPEG size 200kb max" [value]="filePhotoInfo" disabled>
               <div *ngIf="submitted || f.pProfilePhoto.invalid && (f.pProfilePhoto.dirty || f.pProfilePhoto.touched)"
                class="alert alert-danger">
                <div *ngIf="f.pProfilePhoto.errors?.required"> Upload JPEG file and it should not exceed 200kb</div>
              </div> 
              <button type="button" class="btn btn-outline-primary btn-upload"><i class="fas fa fa-cloud-upload"></i>
                Upload File

                <input
                      formControlName="pProfilePhoto" 
                      type="file" 
                      (change)="onPhotoSelect($event)"
                      class="form-control" 
                      >
              </button>
            </div>
          </div>

This is part of my Registration ts file

import { Component, OnInit } from '@angular/core';
import { NgbModalConfig, NgbModal } from '@ng-bootstrap/ng-bootstrap';
import { FormBuilder, FormControl, Validators } from '@angular/forms';
import { ActivatedRoute, Router } from '@angular/router';
import { ValidationService } from 'src/app/Services/validation.service';
import { PRegistrationService } from 'src/app/Services/P-Services/p-registration.service';
@Component({
  selector: 'app-p-registration',
  templateUrl: './p-registration.component.html',
  styleUrls: ['./p-registration.component.css', '../../../app.component.css'],
  providers: [NgbModalConfig, NgbModal]

})


export class PRegistrationComponent implements OnInit {
  checkbox1 = false;
  form: any;
  loading = false;
  submitted = false;
  public fileData = {};
   constructor(
    private PRegistrationService : PRegistrationService,
    config: NgbModalConfig,
    private modalService: NgbModal,
    private formBuilder: FormBuilder,
    private route: ActivatedRoute,
    private router: Router,
    private customValidator: ValidationService,
    ) {
    // customize default values of modals used by this component tree
    config.backdrop = 'static';
    config.keyboard = false;
}

ngOnInit() {
  this.form = this.formBuilder.group({
    pName: ['', Validators.required],
      pProfilePhoto: ['', Validators.required],
      pProfilePic: new FormControl(''),
  });
}
// convenience getter for easy access to form fields
  get f() { return this.form.controls; }

  // tslint:disable-next-line: typedef
  onSubmit() {
    this.submitted = true;
    if (this.form.valid) {
      const formData = new FormData();
      formData.append('pProfilePic', this.form.get('pProfilePic').value);
      this.PRegistrationService.pRegistration(this.form.value)
        .subscribe(result => {
          this.router.navigate(['PRegistration']);
        }, (err) => {
          console.log(err);
        });
    }
  }
  // tslint:disable-next-line: typedef
  reset(){
    this.form.reset();
  }
  // tslint:disable-next-line: typedef
  open(content) {
    this.modalService.open(content, { centered: true });
  }


  filePhotoInfo: string ='';

  onPhotoSelect(event) {
  
    if (event.target.files.length > 0) {
      const pProfilePhoto = event.target.files[0];
      console.log('this is ')
      console.log(pProfilePhoto);
      this.filePhotoInfo = `${pProfilePhoto.name}`;
      this.form.patchValue({
        pProfilePic: pProfilePhoto
      });
    }
  }
}

This is part of my service ts file

export class PRegistration {
    public pId: number;
    public pName: string;
    public pProfilePic: File;

    constructor(    
        pId: number,
        pName: string,
        pProfilePic: File) 
        
        {
        this.pId = pId;
        this.pName = pName;
        this.pProfilePic = pProfilePic;
    }    

}

This is part of my Service file

import { Injectable } from '@angular/core';
import { Observable } from 'rxjs';
import {HttpClient,HttpHeaders} from "@angular/common/http";
import { environment } from 'src/environments/environment';
import { PRegistration } from 'src/app/Services/P-Services/p-registration';

@Injectable({
  providedIn: 'root'
})
export class PRegistrationService {
  constructor(private http: HttpClient) { }
  httpOptions = {
    headers: new HttpHeaders({
      'Content-Type':  'application/json',
    })
  }
  pRegistration(p):Observable<any>{

    return this.http.post<PRegistration>(environment.api_url+"save_user",p,this.httpOptions)
  
  }
}

This is part of my model

@Entity
@Table(name = "prepository")
public class PModels {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int pId;
@Column(nullable = false)
private String pName;
private String pProfilePic;

// Constructor, getter and setter, toString

This is part of my service

public void saveUser(String pName,MultipartFile pProfilePic) {
    try {
        String pProfilePic_file = pProfilePic.getOriginalFilename();
        
        InputStream pProfilePic_is = pProfilePic.getInputStream();
        
        String pProfilePic_ts = String.valueOf(System.currentTimeMillis());
        try { Thread.sleep(1);} catch (InterruptedException e) { e.printStackTrace();}
        
        String rand = UUID.randomUUID().toString();
        
        String pProfilePic_name = pProfilePic_ts+rand+pProfilePic_file;
        
    PModels p = new PModels();
    
    p.setpName(pName);
    p.setpProfilePic(pProfilePic_name);

    pDao.save(p);
    
    String folder = "//Users//Desktop//p//";
    Path path = Paths.get(folder);
    if (!Files.exists(path)) {
        try {
            Files.createDirectory(path);

            }
        catch (IOException e) {
            e.printStackTrace();
            }
        System.out.println("Directory created");
        }
    else {
        System.out.println("Directory already exists");
        }
    folder = folder + p.getPId() + "//";
    Path path1 = Paths.get(folder);
    if (!Files.exists(path1)) {
        try {
            Files.createDirectory(path1);
        }
        catch (IOException e) {
            e.printStackTrace();
            }
        System.out.println("Directory created");
        }
    else {
        System.out.println("Directory already exists");
        }
      Files.copy(pProfilePic_is,Paths.get(folder+pProfilePic_name),StandardCopyOption.REPLACE_EXISTING);
  
  
} catch (IOException e) {
    e.printStackTrace();
}
    
}

This is part of my controller

@PostMapping("/save_user")
     
    
      public void saveUser(@RequestBody PModels pModels) {
      this.pInfo.saveUser(pModels);
      
      System.out.println(pModels.getpName()); // Just for checking

Answer 1

In you case, the Spring Framework assumes that the incoming data is encoded as application/json but it is indeed encoded as multiparty/form-data. First of all, you need to set the ‚consumes' attribute of the @PostMapping annotation. Then you need to use the @RequestPart annotation instead of the @RequestBody one.

I think this blog post shows how to do it.

If I may add another hint: Usually, it's not a good idea to have the same POJO (class) representing both, the DB entity and the DTO for the web service.