How to make both validation annotations in a ConfigurationProperties bean and a #FeignClient interface work together? - spring-boot

Question

Let's say I have this application.yml (which will be environment-dependent e.g. via Spring profiles):
app.remote:
url: http://whatever.url.it.is:8080/
and matching Java-style configuration properties class:
#Configuration
#ConfigurationProperties("app.remote")
public class MyRemoteProperties {
#NotBlank
private String url;
// matching getter/setter...
}
I want some kind of client for my remote url:
#Service
#FeignClient(value = "remote", url = "${app.remote.url}")
public interface MyRemote {
#GetMapping("/what/ever/rest/api")
String stuff();
}
Unfortunately I can't get the validation work for MyRemoteProperties e.g. when the app.remote.url property is blank (empty) the application doesn't start (Spring fails at wiring the MyRemote bean) and I get this error:
Caused by: java.lang.IllegalStateException: No Feign Client for
loadBalancing defined. Did you forget to include
spring-cloud-starter-netflix-ribbon?
(and I don't want load-balancing; I assume this is because the URL is empty at some point, then it expects some load-balancer config hence Ribbon here in the error message).
Or maybe I don't known how to plug it into the MyRemote interface's configuration, e.g. I also tried:
#FeignClient(value = "remote", configuration = MyRemoteProperties.class)
But same result.
How do I get this validation thing to work?
pom.xml
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.8.RELEASE</version>
</parent>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-openfeign</artifactId>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>Greenwich.SR3</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
At some point where the interface is called:
#Service
public RandomServiceOrController {
#Autowired
private MyRemote myRemote;
public void processMyStuff() {
// ...
String myStuff = myRemote.stuff();
// ...
}
}

Answer 1

Don't forget the #Validated annotation on your Java properties class:
#Validated
#Configuration
#ConfigurationProperties("app.remote")
public class MyRemoteProperties {
#NotBlank
private String url;
// matching getter/setter...
}
Your application won't start because of the missing property, not because of a non-defined-loadbalancing-client-you-don't-need (thus making its error message more awkward).