Exception Handling dengan Spring

@RestControllerAdvice
public class AdviceKesalahan {

    @ExceptionHandler(TidakDitemukanException.class)
    public ProblemDetail tidakDitemukan(TidakDitemukanException e) {
        ProblemDetail pd = ProblemDetail.forStatusAndDetail(
                HttpStatus.NOT_FOUND, e.getMessage());
        pd.setTitle("Resource tidak ditemukan");
        return pd;
    }

    @ExceptionHandler(MethodArgumentNotValidException.class)
    public ProblemDetail validasi(MethodArgumentNotValidException e) {
        ProblemDetail pd = ProblemDetail.forStatusAndDetail(
                HttpStatus.BAD_REQUEST, "Input tidak valid");
        pd.setTitle("Validasi gagal");
        pd.setProperty("field", e.getBindingResult().getFieldErrors().stream()
                .map(fe -> fe.getField() + ": " + fe.getDefaultMessage())
                .toList());
        return pd;
    }

    @ExceptionHandler(Exception.class)
    public ProblemDetail takTerduga(Exception e) {
        return ProblemDetail.forStatusAndDetail(
                HttpStatus.INTERNAL_SERVER_ERROR, "kesalahan tak terduga");
    }
}

import java.util.LinkedHashMap;
import java.util.Map;
import java.util.function.Function;

public class PetaHandlerError {

    // Hierarki exception domain ala aplikasi nyata.
    static class KesalahanApi extends RuntimeException {
        KesalahanApi(String pesan) { super(pesan); }
    }

    static class TidakDitemukanException extends KesalahanApi {
        TidakDitemukanException(String pesan) { super(pesan); }
    }

    static class ValidasiGagalException extends KesalahanApi {
        ValidasiGagalException(String pesan) { super(pesan); }
    }

    // RFC 7807 ProblemDetail: format kesalahan baku Spring Boot 3.
    record ProblemDetail(int status, String title, String detail) {
        String json() {
            return "{\"type\":\"about:blank\",\"title\":\"" + title
                    + "\",\"status\":" + status
                    + ",\"detail\":\"" + detail + "\"}";
        }
    }

    public static void main(String[] args) {
        // @RestControllerAdvice mini: exception -> handler.
        Map<Class<? extends Throwable>, Function<Throwable, ProblemDetail>> advice =
                new LinkedHashMap<>();
        advice.put(TidakDitemukanException.class,
                e -> new ProblemDetail(404, "Not Found", e.getMessage()));
        advice.put(ValidasiGagalException.class,
                e -> new ProblemDetail(400, "Bad Request", e.getMessage()));
        advice.put(RuntimeException.class,
                e -> new ProblemDetail(500, "Internal Server Error", "kesalahan tak terduga"));

        layani(advice, "GET /api/produk/99", () -> {
            throw new TidakDitemukanException("Produk 99 tidak ada");
        });
        layani(advice, "POST /api/produk", () -> {
            throw new ValidasiGagalException("Kolom nama tidak boleh kosong");
        });
        layani(advice, "GET /api/laporan", () -> {
            throw new IllegalStateException("sambungan basis data terputus");
        });
    }

    static void layani(Map<Class<? extends Throwable>, Function<Throwable, ProblemDetail>> advice,
                       String permintaan, Runnable handler) {
        System.out.println("Request: " + permintaan);
        try {
            handler.run();
        } catch (Throwable e) {
            ProblemDetail pd = cariHandlerTerdekat(advice, e).apply(e);
            System.out.println("  -> " + pd.status() + " " + pd.title());
            System.out.println("  -> " + pd.json());
            System.out.println();
        }
    }

    // Pencarian handler: naik dari kelas exception konkret ke induknya,
    // persis resolusi @ExceptionHandler pada @ControllerAdvice.
    static Function<Throwable, ProblemDetail> cariHandlerTerdekat(
            Map<Class<? extends Throwable>, Function<Throwable, ProblemDetail>> advice,
            Throwable e) {
        Class<?> kelas = e.getClass();
        while (kelas != null) {
            Function<Throwable, ProblemDetail> handler = advice.get(kelas);
            if (handler != null) {
                return handler;
            }
            kelas = kelas.getSuperclass();
        }
        return x -> new ProblemDetail(500, "Internal Server Error", x.getMessage());
    }
}

Request: GET /api/produk/99
  -> 404 Not Found
  -> {"type":"about:blank","title":"Not Found","status":404,"detail":"Produk 99 tidak ada"}

Request: POST /api/produk
  -> 400 Bad Request
  -> {"type":"about:blank","title":"Bad Request","status":400,"detail":"Kolom nama tidak boleh kosong"}

Request: GET /api/laporan
  -> 500 Internal Server Error
  -> {"type":"about:blank","title":"Internal Server Error","status":500,"detail":"kesalahan tak terduga"}