Defining External Configuration

Configuration values can be defined in the application.yml file to externalize settings from the application logic.

server:
  port: 9000
  servlet:
    context-path: /api

app:
  config:
    service-name: "user-auth-service"
    build-version: 2.5.1

Method 1: Using the @Value Annotation

The @Value annotation allows for direct injection of property values into fields. This approach is suitable for simple use cases where only a few distinct properties are needed.

Controller Implementation

import org.springframework.beans.factory.annotation.Value;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import lombok.extern.slf4j.Slf4j;

@Slf4j
@RestController
@RequestMapping("/config")
public class ValueInjectionController {

    @Value("${app.config.service-name}")
    private String serviceName;

    @Value("${app.config.build-version}")
    private String appVersion;

    @GetMapping("/value")
    public void fetchViaValue() {
        log.info("Service: {}, Version: {}", serviceName, appVersion);
    }
}

Method 2: Type-safe Configuration with @ConfigurationProperties

For grouping related configurations, creating a dedicated configuration class using @ConfigurationProperties is recommended. This method provides type safety and better organization for complex data structures.

Configuration Properties Class

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;
import lombok.Data;

@Data
@Component
@ConfigurationProperties(prefix = "app.config")
public class AppConfigProperties {
    private String serviceName;
    private String buildVersion;
}

Controller Implementation

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import lombok.extern.slf4j.Slf4j;

@Slf4j
@RestController
@RequestMapping("/properties")
public class PropertiesInjectionController {

    private final AppConfigProperties appConfigProperties;

    @Autowired
    public PropertiesInjectionController(AppConfigProperties appConfigProperties) {
        this.appConfigProperties = appConfigProperties;
    }

    @GetMapping("/bean")
    public void fetchViaPropertiesBean() {
        log.info("Retrieved Config - Name: {}, Ver: {}", 
                 appConfigProperties.getServiceName(), 
                 appConfigProperties.getBuildVersion());
    }
}