https://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#howto.application.failure-analyzer
    https://docs.spring.io/spring-boot/docs/3.2.2/api/org/springframework/boot/diagnostics/FailureAnalyzer.html
    https://docs.spring.io/spring-boot/docs/3.2.2/api/org/springframework/boot/diagnostics/FailureAnalysis.html

baeldung
https://www.baeldung.com/exception-handling-for-rest-with-spring
2024
Otus - Exceptions from Java to Spring 1:55:00 of 2:15:46
    https://www.youtube.com/watch?v=dsSFmPeUezY
    ! 15:00 - hierarchy
BusyCoderAcademy - 5. Spring Boot Rest Project Employee Mgt Application with Ex handling Validation||Rajeev Gupta of 1:31:30
    https://www.youtube.com/watch?v=XTk6fz1i9UA
    ! package for exceptions
    ! 44:00 proper way is to create separate @RestControllerAdvice EmployeeAppExHandlerController
    !   create @Data ErrorInfo // dto
    ...
    import org.springframework.http.ResponseEntity;
    import org.springframework.web.bind.annotation.ExceptionHandler;
    import org.springframework.web.bind.annotation.RestControllerAdvice;
    ...
    @RestControllerAdvice
    public class EmployeeAppExHandlerController {
        @ExceptionHandler
        public ResponseEntity<ErrorInfo> handle4042(EmployeeNotFoundException e) {
            var errorInfo = ErrorInfo.builder()
                .errorMessage(e.getMessage())
                .timeStamp(LocalDateTime.now())
                .toContact("firs.last@yopmail.com")
                .statusCode(HttpStatus.NOT_FOUND.toString())
                .build();
            return ResponseEntity.status(HttpStatus.NOT_FOUND)
                .body(errorInfo);
        }
    }
    !
    ! add spring-boot-starter-validation
    ! Dto-classes to transfer data between controller/service layer
    ! GenerateAllSetter idea plugin to convert one objecto into the other
    ! Entity-Corruption pattern - controller-layer should not talk to entities
    !
    @ExceptionHandler(MethodArgumentNotValidException.class)
    public ResponseEntity<ErrorInfo> handle400(MethodArgumentNotValidException e) {
        String errorMessage = e.getBindingResult().getAllErrors().stream().map(e -> e.getDefaultMessage())
        ...
    }

    src/main/resources/ValidationMessages.properties
    employeeDto.name.absent=...
    employeeDto.email.absent=...

    public class EmployeeDto {
       ...
       @NotEmpty(message="{employeeDto.name.absent}")
       private String name;

       @Email(message="...")
       private String email;
       ...
    }

2023
https://blog.stackademic.com/mastering-exception-handling-in-spring-boot-33d74a1dfc9e
https://dip-mazumder.medium.com/spring-boot-exception-handling-best-practices-e8ebe97e8ce
2021
https://dzone.com/articles/spring-boot-exception-handling
    https://github.com/SeunMatt/smattme-tutorials/tree/master/spring-boot-exception-handling
2020
https://reflectoring.io/spring-boot-exception-handling/
    https://github.com/thombergs/code-examples/tree/master/spring-boot/exception-handling
2019
https://thepracticaldeveloper.com/2019/09/09/custom-error-handling-rest-controllers-spring-boot/
https://dzone.com/articles/spring-rest-service-exception-handling-1
2018
https://dzone.com/articles/customize-error-responses-in-spring-boot

public enum ErrorMessages {
    MISSING_REQUIRED_FIELD("BlaBla..."),
    RECORD_ALREADY_EXISTS("AnotherBla...")

    private String errorMessage;

    public ErrorMessage(String errorMessage) {
        this.errorMessage = errorMessage;
    }

    public String getErrorMessage() {
        return errorMessage;
    }
}

public class UserRestController {
    @PostMapping(...)
    public User createUser(@RequestBody UserDetailsRequestModel userDetails) throws Exception {
        if () {
            throw new Exception(ErrorMessage.MISSING_REQUIRED_FIELD.getErrorMessage());
            //  {
            //    "timestamp": "2018-05-09...",
            //    "status": 500,
            //    "error": "Internal Server Error",
            //    "message": "BlaBla...",
            //    "path": "/users"
            //  }
        }
    }
}

package ...exception.UserServiceException;

public class UserServiceException extend RuntimeException {
    private static final long serialVersionUID = 134l...L;

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

public class UserRestController {
    @PostMapping(...)
    public User createUser(@RequestBody UserDetailsRequestModel userDetails) throws UserServiceException {
        if () {
            throw new UserServiceException(ErrorMessage.MISSING_REQUIRED_FIELD.getErrorMessage());
        }
    }
}

package ...exceptions.AppExceptionsHandler;

import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.context.Request.WebRequest;

@ControllerAdvice
public class AppExceptionsHandler {

    @ExceptionHandler(value = {UserServiceException.class}) 
    public ResponseEntity<Object> handleUserServiceException(UserServiceException ex, WebRequest request) {
        return new ResponseEntity<>(ex.getMessage, new HTTPHeaders(), HTTPStatus.INTERNAL_SERVER_ERROR);
        // no Accept headers
    }
}

public class ErrorMessage {
    private Date timestamp;
    private String errorMessage;

    public ErrorMessage() {
    }

    // getters/setters
}

@ControllerAdvice
public class AppExceptionsHandler {

    @ExceptionHandler(value = {UserServiceException.class}) 
    public ResponseEntity<Object> handleUserServiceException(UserServiceException ex, WebRequest request) {
        ErrorMessage errorMessage = new ErrorMessage(new Date(), ex.getMessage());
        return new ResponseEntity<>(errorMessage, new HTTPHeaders(), HTTPStatus.INTERNAL_SERVER_ERROR);
        // now we can use headers
    }
    @ExceptionHandler(value = {Exception.class}) 
    public ResponseEntity<Object> handleOtherException(Exception ex, WebRequest request) {
        ErrorMessage errorMessage = new ErrorMessage(new Date(), ex.getMessage());
        return new ResponseEntity<>(errorMessage, new HTTPHeaders(), HTTPStatus.INTERNAL_SERVER_ERROR);
    }
}