BuyerService.java

package com.gyansagar.services;

import com.gyansagar.exceptions.DuplicateEntryException;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import com.gyansagar.entities.Buyer;
import com.gyansagar.repository.BuyerRepository;

@Service
public class BuyerService 
{
	@Autowired
	BuyerRepository brepo;
	
	public Buyer add(Buyer b) throws DuplicateEntryException {
			try{
				return brepo.save(b);

			}catch (Exception e){
				throw new DuplicateEntryException("Record already exist");
			}



	}

}

DuplicateEntryException.java

package com.gyansagar.exceptions;

public class DuplicateEntryException extends Exception {
    public DuplicateEntryException() {
        super("Resource already exists.");
    }

    public DuplicateEntryException(String message) {
        super(message);
    }

    public DuplicateEntryException(String message, Throwable cause) {
        super(message, cause);
    }

    public DuplicateEntryException(Throwable cause) {
        super(cause);
    }
}

GlobalExceptionHandler.java

package com.gyansagar.exceptions;

import com.gyansagar.dto.ErrorDto;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.validation.FieldError;
import org.springframework.web.bind.MethodArgumentNotValidException;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.context.request.WebRequest;
import org.springframework.web.servlet.mvc.method.annotation.ResponseEntityExceptionHandler;

import java.util.HashMap;
import java.util.Map;

@ControllerAdvice
@RestController
public class GlobalExceptionHandler extends ResponseEntityExceptionHandler {

    @ExceptionHandler({NotFoundException.class})
    public final ResponseEntity handleNotFountExceptions(Exception ex, WebRequest request) {
        ErrorDto response = new ErrorDto(ex.getMessage());
        return new ResponseEntity(response, HttpStatus.NOT_FOUND);
    }

    @ExceptionHandler(DuplicateEntryException.class)
    public final ResponseEntity handleNotFountExceptions1(Exception ex, WebRequest request) {
        ErrorDto response = new ErrorDto(ex.getMessage());
        return new ResponseEntity(response, HttpStatus.NOT_FOUND);
    }

    @Override
    protected ResponseEntity<Object> handleMethodArgumentNotValid(
            MethodArgumentNotValidException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {
        Map<String, String> errors = new HashMap<>();
        ex.getBindingResult().getAllErrors().forEach((error) -> {
            String fieldName = ((FieldError) error).getField();
            String errorMessage = error.getDefaultMessage();
            errors.put(fieldName, errorMessage);
        });

        ErrorDto response = new ErrorDto(ex.getMessage());

        return handleExceptionInternal(ex, response, headers, status, request);
    }

}   

LoginController.java

package com.gyansagar.controllers;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;

import com.gyansagar.dto.ErrorDto;
import com.gyansagar.entities.Login;
import com.gyansagar.exceptions.NotFoundException;
import com.gyansagar.services.LoginService;

@CrossOrigin(origins = "http://localhost:3000")
@RestController
public class LoginController 
{
	
	
	@Autowired
	LoginService lservice;
	
	@PostMapping("/logincheck")
	public Object checkLogin(@RequestBody Login l) throws NotFoundException {

			return lservice.checkLogin(l.getUsername(), l.getPassword());
		

		
	}

}