Now that you have stood up a Config Server, you need to stand up a new Spring Boot application that uses the Config Server to load its own configuration and that refreshes its configuration to reflect changes to the Config Server on-demand, without restarting the JVM. To do so, add the org.springframework.cloud:spring-cloud-starter-config dependency, to connect to the Config Server. Spring sees the configuration property files, as it would any property file loaded from application.properties or application.yml or any other PropertySource.
The properties to configure the Config Client must necessarily be read in before the rest of the application’s configuration is read from the Config Server, during the bootstrap phase. Specify the client’s spring.application.name as a-bootiful-client and the location of the Config Server (spring.cloud.config.uri) in configuration-client/src/main/resources/bootstrap.properties, where it will be loaded earlier than any other configuration. The following listing shows that file:
configuration-client/src/main/resources/bootstrap.properties
spring.application.name=a-bootiful-client
N.B. this is the default:
spring.cloud.config.uri=http://localhost:8888
You also want to enable the /refresh endpoint, to demonstrate dynamic configuration changes. The following listing (from configuration-client/src/main/resources/application.properties) shows how to do so:
management.endpoints.web.exposure.include=*
The client can access any value in the Config Server by using the traditional mechanisms (such as @ConfigurationProperties or @Value("${…}") or through the Environment abstraction). Now you need to create a Spring MVC REST controller that returns the resolved message property’s value. See the Building a RESTful Web Service guide to learn more about building REST services with Spring MVC and Spring Boot.
By default, the configuration values are read on the client’s startup and not again. You can force a bean to refresh its configuration (that is, to pull updated values from the Config Server) by annotating the MessageRestController with the Spring Cloud Config @RefreshScope and then triggering a refresh event. The following listing (from configuration-client/src/main/java/com/example/configurationclient/ConfigurationClientApplication.java) shows how to do so:
package com.example.configurationclient;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.context.config.annotation.RefreshScope;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@SpringBootApplication
public class ConfigurationClientApplication {
public static void main(String[] args) {
SpringApplication.run(ConfigurationClientApplication.class, args);
}
}
@RefreshScope
@RestController
class MessageRestController {
@Value("${message:Hello default}")
private String message;
@RequestMapping("/message")
String getMessage() {
return this.message;
}
}
