Kada smo redefinirali korporativnu platformu, naučili smo da glavna stvar koja je učinila klijente nesretnima nije bila performanse ili korisnički sučelje; to su bile greške koje nisu popravljene koje su uništile procese. U Spring Bootu ili sličnim obrascima u drugim okvirima, osigurajte da se sustavi ponašaju kako se očekuje kada su pod stresom. @ControllerAdvice Why This Matters Kada postavite REST API-je u , brzo ćete se suočiti s ovim problemom: Spring Boot “ ” How do I handle errors neatly without writing repetitive try-catch blocks everywhere? Zamislite da imate Svatko može propustiti s , nevažeći unos ili nedostaje resurs. Umjesto da vraćate zamagljene stack tragove, želite . 50+ endpoints Null pointer iznimka consistent, meaningful, and client-friendly error responses To je mjesto gdje dolazi – centralizira sve upravljanje pogreškama na jednom mjestu. Hajdemo vidjeti Izgraditi ovaj korak po korak, uz primjer iz stvarnog svijeta. @ControllerAdvice how Use Case — User Management REST API Stvorit ćemo a To podupire: simple User API 
 
 
 
 
 
 Fetching users 
 
 Creating users 
 
 
 Simulating failures for testing Our goal → build a   that returns clean JSON responses. unified global error-handling layer Step 1: Project Setup Dependencies (Maven): <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-validation</artifactId>
    </dependency>
 This brings in web + validation support. Then create your main app: @SpringBootApplication
public class ExceptionHandlerDemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(ExceptionHandlerDemoApplication.class, args);
    }
}
 Step 2: Define the Entity — User.java @Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private int id;
    @NotBlank(message = "Name cannot be blank")
    private String name;
    @Min(value = 18, message = "Age must be at least 18")
    private int age;
}
 • Zašto: ** Dodali smo jednostavne validacije tako da Spring može automatski pokrenuti Metodski argument Nevažeća iznimka kada je unos nevažeći. Step 3: Custom Exception for Missing Data public class ResourceNotFoundException extends RuntimeException {
    public ResourceNotFoundException(String message) {
        super(message);
    }
}
public class InvalidRequestException extends RuntimeException {
    public InvalidRequestException(String message) {
        super(message);
    }
}
 • Zašto: **Predstaviti situaciju "korisnik nije pronađen" čisto umjesto generičkih iznimaka. Step 4: Build the Controller @RestController
@RequestMapping("/api/users")
public class UserController {
    // Simple GET that throws ResourceNotFoundException for id > 100
    @GetMapping("/{id}")
    public String getUser(@PathVariable("id") @Min(1) Integer id) {
        if (id > 100) {
            throw new ResourceNotFoundException("User with id " + id + " not found");
        }
        return "User-" + id;
    }
    // Create user example to demonstrate validation
    public static record CreateUserRequest(
            @NotBlank(message = "name is required") String name,
            @Min(value = 18, message = "age must be >= 18") int age) {}
    @PostMapping
    @ResponseStatus(HttpStatus.CREATED)
    public String createUser(@RequestBody @Valid CreateUserRequest body) {
        if ("bad".equalsIgnoreCase(body.name())) {
            throw new InvalidRequestException("Name 'bad' is not allowed");
        }
        return "created:" + body.name();
    }
    // Endpoint to force a server error for demo
    @GetMapping("/boom")
    public void boom() {
        throw new IllegalStateException("simulated server error");
    }
}
 • Zašto: ** Kreiramo realistične scenarije – ne pronađene, pogreške validiranja i pogreške u radnom vremenu – koje će upravljati naš globalni upravljač. Step 5: Create a Standard Error Model @Data
@AllArgsConstructor
@NoArgsConstructor
public class ErrorResponse {
    private OffsetDateTime timestamp;
    private int status;
    private String error;
    private String message;
    private String path;
    private List<FieldError> fieldErrors;}
 • Zašto: **Svi API-ji trebaju vratiti pogreške u istoj strukturi - to poboljšava praćenje i debugiranje u proizvodnji. Step 6: Implement @ControllerAdvice (Global Handler) @ControllerAdvice
public class GlobalExceptionHandler {
    private final Logger log = LoggerFactory.getLogger(GlobalExceptionHandler.class);
    // Handle custom validation exceptions
    @ExceptionHandler(InvalidRequestException.class)
    public ResponseEntity<ErrorResponse> handleInvalidRequest(InvalidRequestException ex, HttpServletRequest req) {
        log.debug("InvalidRequestException: {}", ex.getMessage());
        ErrorResponse body = new ErrorResponse(OffsetDateTime.now(), HttpStatus.BAD_REQUEST.value(),
                HttpStatus.BAD_REQUEST.getReasonPhrase(), ex.getMessage(), req.getRequestURI());
        return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(body);
    }
    // Resource not found -> 404
    @ExceptionHandler(ResourceNotFoundException.class)
    public ResponseEntity<ErrorResponse> handleNotFound(ResourceNotFoundException ex, HttpServletRequest req) {
        log.debug("ResourceNotFoundException: {}", ex.getMessage());
        ErrorResponse body = new ErrorResponse(OffsetDateTime.now(), HttpStatus.NOT_FOUND.value(),
                HttpStatus.NOT_FOUND.getReasonPhrase(), ex.getMessage(), req.getRequestURI());
        return ResponseEntity.status(HttpStatus.NOT_FOUND).body(body);
    }
    // Validation errors from @Valid on request bodies
    @ExceptionHandler(MethodArgumentNotValidException.class)
    public ResponseEntity<ErrorResponse> handleValidation(MethodArgumentNotValidException ex, HttpServletRequest req) {
        log.debug("Validation failed: {}", ex.getMessage());
        List<ErrorResponse.FieldError> fieldErrors = ex.getBindingResult().getFieldErrors().stream()
                .map(fe -> new ErrorResponse.FieldError(fe.getField(), fe.getRejectedValue(), fe.getDefaultMessage()))
                .collect(Collectors.toList());
        ErrorResponse body = new ErrorResponse(OffsetDateTime.now(), HttpStatus.BAD_REQUEST.value(),
                HttpStatus.BAD_REQUEST.getReasonPhrase(), "Validation failed", req.getRequestURI());
        body.setFieldErrors(fieldErrors);
        return ResponseEntity.badRequest().body(body);
    }
    // Type mismatch for method args (?id=abc)
    @ExceptionHandler(MethodArgumentTypeMismatchException.class)
    public ResponseEntity<ErrorResponse> handleTypeMismatch(MethodArgumentTypeMismatchException ex, HttpServletRequest req) {
        log.debug("Type mismatch: {}", ex.getMessage());
        ErrorResponse body = new ErrorResponse(OffsetDateTime.now(), HttpStatus.BAD_REQUEST.value(),
                HttpStatus.BAD_REQUEST.getReasonPhrase(), ex.getMessage(), req.getRequestURI());
        return ResponseEntity.badRequest().body(body);
    }
    // No handler found (404 for unmatched endpoints)
    @ExceptionHandler(NoHandlerFoundException.class)
    public ResponseEntity<ErrorResponse> handleNoHandler(NoHandlerFoundException ex, HttpServletRequest req) {
        log.debug("NoHandlerFound: {} {}", ex.getHttpMethod(), ex.getRequestURL());
        ErrorResponse body = new ErrorResponse(OffsetDateTime.now(), HttpStatus.NOT_FOUND.value(),
                HttpStatus.NOT_FOUND.getReasonPhrase(), "Endpoint not found", req.getRequestURL().toString());
        return ResponseEntity.status(HttpStatus.NOT_FOUND).body(body);
    }
    // Generic fallback
    @ExceptionHandler(Exception.class)
    public ResponseEntity<ErrorResponse> handleAll(Exception ex, HttpServletRequest req) {
        log.error("Unhandled exception: ", ex);
        ErrorResponse body = new ErrorResponse(OffsetDateTime.now(), HttpStatus.INTERNAL_SERVER_ERROR.value(),
                HttpStatus.INTERNAL_SERVER_ERROR.getReasonPhrase(), "An internal error occurred", req.getRequestURI());
        return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body(body);
    }
}
 Why: 
 
 
 
 @ControllerAdvice → Omogućuje globalno korištenje svih kontrolera. @IzuzetakHandler → Uhvati specifične vrste iznimaka. Pomoćnik buildResponse() čuva kod DRY i čist. Step 7: Test Scenarios   GET /api/users/1 Kod odgovora: 200 -Uspjeh » » GET /api/users/999 Kod odgovora: 404 Resource Not Found » » Validation Error POST / API / korisnici {"name":"", "age": 15} Response: » » Unexpected Error GET /api/korisnici / Boom » » Why This Approach Works in Real Projects 
 
 
 
 
 
 
 
 
 
 Problem 
 Solution 
 
 
 
 Too many try-catch blocks 
 Centralized handling with @ControllerAdvice 
 
 
 
 Inconsistent responses 
 Unified ErrorResponse structure 
 
 
 
 Hard to debug 
 Standardized messages with timestamps and paths 
 
 
 
 Client confusion 
 Clear, meaningful messages for each failure type Previše try-catch blokova Centralizirano rukovanje pomoću @ControllerAdvice Nedosljedni odgovori Unified ErrorResponse struktura Teško je debugirati Standardizirane poruke s vremenskim žigovima i putovima Klijenti zbunjuju Jasne, značajne poruke za svaki tip neuspjeha Real-World Usage Scenarios 
 
 
 
 
 Bankarske API-je: osigurajte da pogreške u validaciji (kao što je nevažeći broj računa) ne ometaju uslugu. E-trgovina: Graciozno upravljajte neotkrivenim proizvodima ili greškama u plaćanju. Data Microservices: vraća strukturirane poruke kada ulazni podaci ne validiraju. API Gateway: dosljedni odgovori na više mikroslužbi. Final Thoughts Kombiniranjem @ControllerAdvice, @ExceptionHandler i jednostavnog modela odgovora na pogrešku dobivate: 
 
 
 
 Čisti kod Dosljedno API iskustvo Lakše debugiranje u proizvodnji To je jedan od najjednostavnijih, ali najmoćnijih dizajnerskih uzoraka u razvoju Spring Boota.

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