# custom-validation

Companion module for [**Custom Validation in Spring Boot: Beyond the Basics!**](https://ankurm.com/custom-validation-in-spring-boot-beyond-the-basics/)
on ankurm.com, rewritten around **Jakarta Validation 3.1** (Spring Boot 4.1.1 / Hibernate Validator
9.1.3.Final) and the `jakarta.validation` namespace the original article's `javax.validation` code
never actually ran under on Boot 3+.

`mvn test` regenerates every transcript in [`docs/output/`](docs/output) -- the test suite is the
transcript generator.

## Versions

| | |
|---|---|
| Spring Boot | 4.1.1 |
| Spring Framework | 7.0.9 |
| Hibernate Validator | 9.1.3.Final (`jakarta.validation-api` 3.1.1) -- confirmed with `mvn dependency:tree` and by reading the jars' own manifests, see [docs/01](docs/01-jakarta-namespace-and-bean-validation-3-1.md) |
| JDK | Eclipse Temurin 25.0.4.1 (LTS) |

## Quickstart

```bash
export JAVA_HOME=/path/to/jdk-25
mvn -DskipTests package
./scripts/run.sh                 # port 8080
curl -s -X POST localhost:8080/contact -H 'Content-Type: application/json' \
     -d '{"email":"user@example.com","message":"hello there, this message is long enough"}'
mvn test                         # 10 tests, regenerates docs/output/
```

## Endpoints

| Endpoint | Shows |
|---|---|
| `POST /contact` | field-level custom constraint (`@SpamMessageCheck`), class-based DTO, `BindingResult` |
| `POST /contact-record` | the same constraint on a record component |
| `POST /booking` | class-level (cross-field) custom constraint (`@DateRangeValid`), class-based DTO |
| `POST /booking-record` | the same cross-field constraint on a record's type declaration |
| `GET /diagnostic/validation-provider` | prints the real Bean Validation provider and spec version at runtime -- delete before shipping |

## Documentation

1. [The jakarta.validation namespace, and what Bean Validation 3.1 actually changed](docs/01-jakarta-namespace-and-bean-validation-3-1.md)
2. [Record validation, field-level and class-level](docs/02-record-validation.md)
3. [What the defaults do not do: record validation failures with no error body](docs/03-what-the-defaults-do-not-do.md)

## Findings worth the trip

- **The original article's `javax.validation.*` imports never worked on Spring Boot 3+.** Boot 3
  moved entirely to the `jakarta.*` namespace in December 2022; this module is the corrected,
  runnable version.
- **Spring Boot 4.1.1 pins Hibernate Validator 9.1.3.Final / Jakarta Validation 3.1**, confirmed
  by `mvn dependency:tree` and independently by reading the actual jar manifests at test time.
- **A record validation failure with no `BindingResult` in the controller signature returns an
  EMPTY 400 body by default** -- not a JSON error, not even with `Accept: application/json`.
- **`spring.mvc.problemdetails.enabled=true` fixes the empty body but not the missing detail**:
  the resulting `ProblemDetail` is generic (`"Invalid request content."`), with no per-field
  messages, unless you write a custom `@ExceptionHandler` to put them there yourself.
- **`AutoConfigureMockMvc` moved packages in Boot 4.1**, from
  `org.springframework.boot.test.autoconfigure.web.servlet` to
  `org.springframework.boot.webmvc.test.autoconfigure` -- and `spring-boot-starter-test` alone no
  longer pulls in MockMvc's autoconfiguration; that needs `spring-boot-starter-webmvc-test`.

## License

MIT -- see [LICENSE](../LICENSE).