Spring Boot 4 Microservices & REST APIs · Pelajaran

Validator Kustom

Tulis batasan validasi Anda sendiri.

Validator Kustom adalah pelajaran Spring Boot 4 Microservices & REST APIs gratis di CoddyKit. Ini adalah pelajaran 2 dari 4. Kamu bisa membaca pelajaran lengkapnya di bawah secara gratis — lalu praktikkan langsung di browser dengan editor kode bawaan dan tutor AI 24/7. Ini adalah bagian dari jalur belajar Spring Boot 4 Microservices & REST APIs, dan progresmu tersinkronisasi di web dan aplikasi CoddyKit. Kursus Spring Boot 4 Microservices & REST APIs mencakup 4 pelajaran total.

Bagian dari pelajaran ini belum diterjemahkan dan ditampilkan dalam bahasa Inggris.

When Built-ins Are Not Enough

Standard constraints cannot express every rule — a valid coupon code format, a phone number for a region, or a value that must exist in the database. For these you write a custom constraint backed by a validator.

Two Parts of a Custom Constraint

A custom constraint has two pieces:

An annotation that you place on fields or parameters
A ConstraintValidator that contains the actual checking logic

Defining the Annotation

Create the annotation and link it to its validator with @Constraint. Declare the standard message, groups, and payload members required by the spec.

@Target({ FIELD, PARAMETER })
@Retention(RUNTIME)
@Constraint(validatedBy = StrongPasswordValidator.class)
public @interface StrongPassword {
    String message() default "Password is not strong enough";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
}

Implementing ConstraintValidator

The validator implements ConstraintValidator<Annotation, Type> and overrides isValid. Return true when the value satisfies the rule.

public class StrongPasswordValidator
        implements ConstraintValidator<StrongPassword, String> {
    @Override
    public boolean isValid(String value, ConstraintValidatorContext ctx) {
        if (value == null) return true; // let @NotNull handle null
        return value.length() >= 8
            && value.chars().anyMatch(Character::isDigit)
            && value.chars().anyMatch(Character::isUpperCase);
    }
}

Null-Handling Convention

By convention a custom validator treats null as valid, delegating null-checking to @NotNull. This keeps constraints composable — each rule does one job.

Using the Custom Constraint

Apply your annotation just like a built-in one. Combined with @Valid on the controller, it participates in the normal validation flow.

public class CreateUserRequest {
    @NotBlank
    @StrongPassword
    private String password;
}

Custom Violation Messages

Inside isValid you can disable the default message and add a contextual one, useful when a single annotation enforces several sub-rules.

ctx.disableDefaultConstraintViolation();
ctx.buildConstraintViolationWithTemplate(
        "Password must include a digit and an uppercase letter")
   .addConstraintViolation();
return false;

Injecting Beans into a Validator

A ConstraintValidator is a Spring bean, so it can use constructor injection — enabling rules that consult a repository or service, such as uniqueness checks.

public class UniqueEmailValidator
        implements ConstraintValidator<UniqueEmail, String> {
    private final UserRepository repo;
    public UniqueEmailValidator(UserRepository repo) { this.repo = repo; }
    @Override
    public boolean isValid(String email, ConstraintValidatorContext ctx) {
        return email == null || !repo.existsByEmail(email);
    }
}

Class-Level Constraints

Some rules span multiple fields — "password must equal confirmPassword." Target the annotation at TYPE and validate the whole object, accessing several fields together.

@Target(TYPE)
@Retention(RUNTIME)
@Constraint(validatedBy = PasswordsMatchValidator.class)
public @interface PasswordsMatch {
    String message() default "Passwords do not match";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
}

Initialization Hook

Override initialize to capture attributes from the annotation instance, such as a configurable minimum length, before validation runs.

@Override
public void initialize(StrongPassword ann) {
    this.minLength = ann.minLength();
}

Keep Validators Pure and Fast

Validators run on every request, so keep them quick and side-effect-free where possible. Database-backed checks are fine but should be indexed and lightweight to avoid slowing request handling.

Quick Check

Test your understanding of custom validators.

Recap

Custom validators extend Bean Validation.

A constraint is an @Constraint annotation plus a ConstraintValidator
Override isValid; treat null as valid by convention
Validators are beans, so they support constructor injection
Use class-level constraints for cross-field rules
Customize messages via the validation context

Pertanyaan yang Sering Diajukan

Apakah pelajaran “Validator Kustom” gratis?

Ya — teks lengkap “Validator Kustom” gratis dibaca di sini di web. Untuk praktiknya secara interaktif (editor kode bawaan dan tutor AI 24/7) dan buka sisa kursus Spring Boot 4 Microservices & REST APIs, upgrade ke CoddyKit PRO. Kursus Spring Boot 4 Microservices & REST APIs mencakup 4 pelajaran total.

Apa yang akan aku pelajari di “Validator Kustom”?

Tulis batasan validasi Anda sendiri. Kamu berlatih Spring Boot 4 Microservices & REST APIs dengan kode praktik yang langsung kamu jalankan di browser, dan tutor AI 24/7 menjawab pertanyaanmu saat kamu mengerjakan pelajaran ini.

Apakah aku perlu pengalaman untuk memulai Spring Boot 4 Microservices & REST APIs?

Tidak diperlukan pengalaman sebelumnya. Spring Boot 4 Microservices & REST APIs di CoddyKit dirancang untuk pemula hingga pelajar tingkat lanjut, jadi kamu bisa memulai di sini atau dari awal dan belajar sesuai kecepatan kamu sendiri. Ini adalah pelajaran 2 dari 4.

Berapa lama pelajaran “Validator Kustom” memakan waktu?

Sebagian besar pelajaran CoddyKit memakan waktu sekitar 5–10 menit. Setiap pelajaran ringkas dan interaktif, jadi kamu membuat kemajuan stabil dan melanjutkan dari tempat kamu tinggalkan di web dan aplikasi.

Bisakah aku menulis dan menjalankan kode dalam pelajaran Spring Boot 4 Microservices & REST APIs ini?

Ya. Setiap pelajaran Spring Boot 4 Microservices & REST APIs menyertakan editor kode bawaan, jadi kamu menulis dan menjalankan kode nyata langsung di browser dan mendapatkan umpan balik AI instan — tidak diperlukan penyiapan lokal.

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