Return JSON object from a spring-boot rest Controller

Question

I'm trying to check if the username is unique in spring-boot. I want to send the result as JSON object. This is the REST controller

@RequestMapping(value="/checkEmailUnique",method=RequestMethod.POST)
public String checkEmailUnique(@RequestBody String username){

    AppUser app = userRepo.findByUsername(username);
    if(app!=null){
        // I want to return somthing like emailNotTaken: true
    }
    else{
        // and here : emailNotTaken: false  
    }
}

I want to get the result in angular so I can show an error message in my component. How can I do that?

Angular side

client.Service.Ts

checkEmailNotTaken(email:string){
    if(this.authService.getToken()==null) {
      this.authService.loadToken();
    }
    return this.http.post(this.host+
      "/checkEmailUnique/",{email},{headers:new HttpHeaders({'Authorization':this.authService.getToken()})});
  }

in client.component.ts

ngOnInit() {

    this.form = this.formBuilder.group({
      prenom: ['', Validators.required],
      nom: ['', Validators.required],
      tel: ['', Validators.required],
      cin: ['', Validators.required],
      username: ['', Validators.required , Validators.email  , this.validateEmailNotTaken.bind(this)],
      passwordG: this.formBuilder.group({
        password: ['',[Validators.required,Validators.minLength(9)]],
        Confirmationpassword : ['',[Validators.required,Validators.minLength(9)]]

      }, {validator: passwordMatch})

    });
  }

    validateEmailNotTaken(control: AbstractControl) {
        return this.clientService.checkEmailNotTaken(control.value).map(res => {
          return  // what to do here ?
        });

      }

EDIT

@RequestMapping(value="/checkEmailUnique",method=RequestMethod.POST)
    public EmailStatusCheckJson checkEmailUnique(@RequestBody final String username){

        final EmailStatusCheckJson returnValue = new EmailStatusCheckJson();


         AppUser app = userRepo.findByUsername(username);


         if(app!=null){
             returnValue.setEmailIsAvailable(false);
         }
         else{
             returnValue.setEmailIsAvailable(true);

         }

         return returnValue;
    }

Answer 1

If you are using the spring-boot-starter-web, your project is already set to return JSON. Instead of String as the return value from checkEmailUnique , use an object type that you create.

Here is an example:

public class EmailStatusCheckJson
{
    private Boolean emailIsAvailable;

    public Boolean getEmailIsAvailable()
    {
        return emailIsAvailable;
    }

    public void setEmailIsAvailable(
        final Boolean newValue)
    {
        emailIsAvailable = newValue
    }
}


@RequestMapping(value="/checkEmailUnique",method=RequestMethod.POST)
public EmailStatusCheckJson checkEmailUnique(@RequestBody final String username)
{
    final EmailStatusCheckJson returnValue = new EmailStatusCheckJson();

    if (...) // email is available.
    {
        returnValue.setEmailIsAvailable(true);
    }
    else
    {
        returnValue.setEmailIsAvailable(false);
    }

    return returnValue;        
}

Edited added more example.

Answer 2

Rest method have a return type as String .In place of any String you can use a user defined object where(inside there) put a boolean variable eg status there you can send whether the username is present or not. According to the response from the rest side you can forward towards angular.

Answer 3

You could also do this way using ResponseEntity as the return value to your RestController

public ResponseEntity<?> checkEmailUnique(@RequestBody String username){
    AppUser app = userRepo.findByUsername(username);
    if(null != app) {
        return ResponseEntity.badRequest().build(); // Will return a 400 response
    }
    return ResponseEntity.ok().build(); // Will return a 200 response
}

Base on the response type you could directly identify if the email exits or not instead of returning json in this case.