Rest API design with Spring Boot

Question

In a recruitment interview I got this small projet to do at home: rest API written in Java using Spring Boot. As I didn't hear back from the company I wanted to have feedback from review. I am a rest api/spring boot beginner.

Requirements: Design a rest API managing horse races and their particpants:

• A race hase a name, date and unique number for that date
• A race has at least 3 participants
• A particpant has a name and an unique id
• The participant in a race have consecutive ids starting with 1

The API must expose methods for:

• Create races
• Create their participants
• Persist both in a sql db
• Add Kafka producer/consumer layer so that the races could be read from systems outside ( As I've never used Kafka, I didn't do that part)

Here is my code, following Controller -> Service -> Repository pattern:

• Domain

/***RACE***/
public interface IRace {
 int MIN_COURSE_SIZE = 3;
 String getName();
 LocalDate getDate();
 int getDayNumber();
 Set<IRunner> getRunners();
 void addRunner(String name);
}
@Entity
@Table(name = "RACE")
@RequiredArgsConstructor
@AllArgsConstructor
public class Race implements IRace {
 private AtomicInteger runnersCount = new AtomicInteger(1);
 @EmbeddedId
 @Getter
 RaceId id;
 @OneToMany(mappedBy = "race", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
 @Getter
 private Set<IRunner> runners = new HashSet<>();
 public Race(RaceId id) {
 this.id = id;
 }
 @Override
 public String getName() {
 return id.getName();
 }
 @Override
 public LocalDate getDate() {
 return id.getDate();
 }
 @Override
 public int getDayNumber() {
 return id.getDayNumber();
 }
 @Override
 public Set<IRunner> getRunners() {
 return runners;
 }
 @Override
 public void addRunner(String name) {
 runners.add(new Runner(name, runnersCount.getAndIncrement(), this));
 }
 @Override
 public int hashCode() {
 return Objects.hash(id.getName(), id.getDate(), id.getDayNumber());
 }
 @Override
 public boolean equals(Object o) {
 if (o == this)
 return true;
 if (!(o instanceof Race))
 return false;
 Race other = (Race) o;
 return this.id.equals(other.id);
 }
 @Override
 public String toString() {
 return "[Race: name=" + getName() + " date=" + getDate() + " dayNumber=" + getDayNumber() + " runners=" + runnersCount;
 }
}
@Embeddable
@NoArgsConstructor
@AllArgsConstructor
public class RaceId implements Serializable {
 private static final long serialVersionUID = -9092062626878526790L;
 @Column(name = "race_name", nullable = false)
 @Getter
 private String name;
 @Column(name = "race_date", nullable = false)
 @Getter
 private LocalDate date;
 @Column(name="race_day_number",nullable = false)
 @Positive
 @Getter
 private int dayNumber;
 @Override
 public int hashCode() {
 return Objects.hash(name, date, dayNumber);
 }
 @Override
 public boolean equals(Object obj) {
 if (obj == this)
 return true;
 if (!(obj instanceof RaceId))
 return false;
 RaceId other = (RaceId) obj;
 return this.name.equals(other.name) && this.date.equals(other.date) && this.dayNumber == other.dayNumber;
 }
 public String getName() {
 return name;
 }
 public LocalDate getDate() {
 return date;
 }
 public int getDayNumber() {
 return dayNumber;
 }
}
public class RaceValidator implements ConstraintValidator<ValidRace, IRace> {
 @Override
 public void initialize(ValidRace constraintAnnotation) {
 ConstraintValidator.super.initialize(constraintAnnotation);
 }
 @Override
 public boolean isValid(IRace race, ConstraintValidatorContext constraintValidatorContext) {
 if (!isValid(race)) {
 throw new IllegalArgumentException("Invalid race");
 }
 return true;
 }
 /**
 * Validates following rules:
 * 1. Course runners must be at least n (n = ICourse.MinCourseSize)
 * 2. Runner numbers must be n first integers starting from 1
 * 3. Runners must all be part of the same race
 *
 * @param race
 * @return true if race satisfies the conditions, false otherwise
 */
 private boolean isValid(IRace race) {
 int n = race.getRunners().size();
 if (n <= IRace.MIN_COURSE_SIZE) {
 return false;
 }
 int validSum = (n * (n + 1)) / 2;
 int sum = race.getRunners().stream().mapToInt(r -> r.getNumber()).sum();
 if (sum != validSum) {
 return false;
 }
 if (!race.getRunners().stream().allMatch(r -> r.getCourse().equals(race))) {
 return false;
 }
 return true;
 }
}
@Constraint(validatedBy = RaceValidator.class)
@Target({ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
public @interface ValidRace {
 String message() default "Invalid course";
 Class<?>[] groups() default {};
 Class<? extends Payload>[] payload() default {};
}
/*** RUNNER ***/
public interface IRunner {
 String getName();
 int getNumber();
 void setNumber(int number);
 IRace getCourse();
}
@Entity
@Table(name = "RUNNER")
@NoArgsConstructor
public class Runner implements IRunner {
 @Id
 @GeneratedValue(strategy = GenerationType.IDENTITY)
 @Getter
 private Long id;
 @Column(name = "NAME", nullable = false)
 @Getter
 private String name;
 @Column(name = "NUMBER")
 @Getter
 @Setter
 private int number;
 @ManyToOne
 @JoinColumns({
 @JoinColumn(
 name = "race_name",
 referencedColumnName = "race_name"),
 @JoinColumn(
 name = "race_date",
 referencedColumnName = "race_date"),
 @JoinColumn(
 name = "race_day_number",
 referencedColumnName = "race_day_number")
 })
 @Getter
 private IRace race;
 public Runner(String name, int number, IRace course) {
 this.name = name;
 this.number = number;
 this.race = course;
 }
 @Override
 public int hashCode() {
 return Objects.hash(name, number, race);
 }
 @Override
 public boolean equals(Object o) {
 if (o == this)
 return true;
 if (!(o instanceof Runner))
 return false;
 Runner other = (Runner) o;
 return this.name.equals(other.name) && this.number == other.number && this.race.equals(other.race);
 }
}

• Repository

public interface RaceRepository extends CrudRepository<IRace, RaceId> {
 Iterable<IRace> findByDate(LocalDate date);
 Optional<IRace> findByDateAndDayNumber(LocalDate date, int dayNumber);
}

• Service

public interface IRaceService {
 IRace save(IRace course);
 Iterable<IRace> findAll();
 Iterable<IRace> findByDate(LocalDate date);
 Optional<IRace> findByDateAndDayNumber(LocalDate date, int dayNumber);
}
@Slf4j
@Service
public class RaceService implements IRaceService {
 @Autowired
 private RaceRepository raceRepository;
 @Override
 public IRace save(IRace race) {
 return raceRepository.save(race);
 }
 @Override
 public Iterable<IRace> findAll() {
 return raceRepository.findAll();
 }
 @Override
 public Iterable<IRace> findByDate(org.joda.time.LocalDate date) {
 return raceRepository.findByDate(date);
 }
 @Override
 public Optional<IRace> findByDateAndDayNumber(LocalDate date, int dayNumber) {
 return raceRepository.findByDateAndDayNumber(date, dayNumber);
 }
}
public class InvalidRaceException extends Exception {
 public InvalidRaceException(String s) {
 super(s);
 }
}

• Controller

/**
 * Generic wrapper for http response
 */
@Data
@SuperBuilder
@JsonInclude(Include.NON_NULL)
public class GenericResponse {
 protected LocalDateTime timeStamp;
 protected HttpStatus httpStatus;
 protected String reason;
 protected String message;
 protected String developerMessage;
 protected Map data;
}
import static org.springframework.http.HttpStatus.CREATED;
import static org.springframework.http.HttpStatus.OK;
@Validated
@Controller
@RequestMapping("/race")
public class RaceController {
 @Autowired
 private IRaceService raceService;
 @GetMapping("/races")
 public ResponseEntity<GenericResponse> findAll() {
 GenericResponse genericResponse = GenericResponse.builder().build();
 genericResponse.timeStamp = LocalDateTime.now();
 genericResponse.data = Map.of("races", raceService.findAll());
 genericResponse.message = "races found";
 genericResponse.httpStatus = OK;
 return ResponseEntity.ok(genericResponse);
 }
 @GetMapping(value = "/race/{date}")
 public ResponseEntity<GenericResponse> findByDate(@PathVariable("date") LocalDate date) {
 GenericResponse genericResponse = GenericResponse.builder().build();
 genericResponse.timeStamp = LocalDateTime.now();
 genericResponse.data = Map.of("races", raceService.findByDate(date));
 genericResponse.message = "races found for date: " + date;
 genericResponse.httpStatus = OK;
 return ResponseEntity.ok(genericResponse);
 }
 @GetMapping(value = "/race", params = {"date", "dayNumber"})
 public ResponseEntity<GenericResponse> findByDateAndDayNumber(@PathVariable("date") LocalDate date, @PathVariable("dayNumber") int dayNumber) {
 GenericResponse genericResponse = GenericResponse.builder().build();
 genericResponse.timeStamp = LocalDateTime.now();
 genericResponse.data = Map.of("races", raceService.findByDateAndDayNumber(date, dayNumber));
 genericResponse.message = "races found";
 genericResponse.httpStatus = OK;
 return ResponseEntity.ok(genericResponse);
 }
 @PostMapping("/race")
 public ResponseEntity<GenericResponse> addRace(@RequestBody @ValidRace IRace race) {
 GenericResponse genericResponse = GenericResponse.builder().build();
 genericResponse.timeStamp = LocalDateTime.now();
 genericResponse.data = Map.of("races", raceService.save(race));
 genericResponse.message = "race created";
 genericResponse.httpStatus = CREATED;
 return ResponseEntity.ok(genericResponse);
 }
 @PostMapping("/race/{runnerName}")
 public ResponseEntity<GenericResponse> addRunner(@RequestBody @ValidRace IRace race, @PathVariable String runnerName) {
 race.addRunner(runnerName);
 GenericResponse genericResponse = GenericResponse.builder().build();
 genericResponse.timeStamp = LocalDateTime.now();
 genericResponse.data = Map.of("races", raceService.save(race));
 genericResponse.message = "race created";
 genericResponse.httpStatus = CREATED;
 return ResponseEntity.ok(genericResponse);
 }
}

Any critics are welcomed. Thank you very much

• Grim: Why havent you concidered to use data-rest? (spring.io/projects/spring-data-rest)

Answer 1

@GetMapping("/races")
public ResponseEntity<GenericResponse> findAll() {
 GenericResponse genericResponse = GenericResponse.builder().build();
 genericResponse.timeStamp = LocalDateTime.now();
 genericResponse.data = Map.of("races", raceService.findAll());
 genericResponse.message = "races found";
 genericResponse.httpStatus = OK;
 return ResponseEntity.ok(genericResponse);
}

findAll seems a problematic If you have a lot of data. you will encounter a lot of heap, and maybe HEAP OVERFLOW. what I will suggest is to use paging, or any other technique that prevent loading all the data in this way. there is a bunch of technique that you can use.

findByDate(org.joda.time.LocalDate date)

once you imported LocalDate, why to put the full path into method parameter ?

throw new IllegalArgumentException("Invalid race");

better to add the id of the race or any thing that indicate to the info for investigation logs.