JarCastingfeign-validation 
A library for Feign containing a decorator which makes it possible to validate reponses using bean validation api 1.1 (JSR 349) or bean validation 2.0 (JSR 380).
While Jersey as the JAX-RS implementation provides Bean Validation Support, Feign acts as a client and til now only supports a limited set of annotations in it's JAX-RS module, meaning @javax.validation.Valid or @javax.validation.groups.ConvertGroup are not supported.
This library contains a decorator class, which can be setup within invocationHandlerFactory to retrieve additional validation.
Motivation
Sometimes it is required, that a client also validates the response it got from the providing service/endpoint. With JSR-349 bean validation, Java provides a nice api for validation purposes. Just by adding annotations like @NotNull or @Email, contraints can be validated very easily. With JSR-380 you even get support for new date/time data types (JSR 310) and more.
Versions
| feign-validation Version | JSR | Validation Api Version |
|---|---|---|
| 1.x | JSR-349 support | javax.validation:validation-api:1.1.0.Final |
| 2.x and beyond | JSR-380 support | javax.validation:validation-api:2.0.1.Final |
Example
Here is how you can activate bean validation within Feign wrapper client:
interface GitHub {
@RequestLine("GET /repos/{owner}/{repo}/contributors")
@Size(min = 1)
@Valid
List<Contributor> contributors(@Param("owner") String owner, @Param("repo") String repo);
}
static class Contributor {
@NotNull
@Size(min = 10)
String login;
int contributions;
}
public static void main(String... args) {
Validator validator = Validation.buildDefaultValidatorFactory().getValidator();
GitHub github = ExtendedFeign.builder(validator)//
.decoder(new GsonDecoder()).target(GitHub.class, "https://api.github.com");
// Fetch and print a list of the contributors to this library.
try {
List<Contributor> contributors = github.contributors("OpenFeign", "feign");
for (Contributor contributor : contributors) {
System.out.println(contributor.login + " (" + contributor.contributions + ")");
}
} catch (ConstraintViolationException ex) {
ex.getConstraintViolations().forEach(System.out::println);
}
}
Download
With JSR-380 support:
<dependency>
<groupId>com.github.mwiede</groupId>
<artifactId>feign-validation</artifactId>
<version>2.0</version>
</dependency>
With JSR-349 support:
<dependency>
<groupId>com.github.mwiede</groupId>
<artifactId>feign-validation</artifactId>
<version>1.0</version>
</dependency>