Environment variable that does not follow guidelines for use of _ is still successfully bound if another property source contains a property that is bound to the same target

[Bert-R]

We have custom properties, built like this:

@ConfigurationProperties("yona")
@Configuration
public class YonaProperties
{
	@NestedConfigurationProperty
	private final AnalysisServiceProperties analysisService = new AnalysisServiceProperties();

Properties would be set on AnalysisServiceProperties in this way:

yona.analysisService.someProperty=someValue

Or through an environment variable, like this:

YONA_ANALYSIS_SERVICE_SOME_PROPERTY=someValue

With Spring Boot 1.5, it was OK to not have any yona.analysisService.xxx property in application.properties and still set one through an environment variable like YONA_ANALYSIS_SERVICE_XXX.

With Spring Boot 2.0.4, that doesn't work anymore. At least one yona.analysisService.xxx must exist in application.properties. It's OK to set xxx in application.properties and yyy through the environment, but there needs to be at least one.

[wilkinsona]

Here's a minimal example that reproduces the behaviour described above:

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.ConfigurableApplicationContext;

@SpringBootApplication
@EnableConfigurationProperties(YonaProperties.class)
public class Gh14479Application {

	public static void main(String[] args) {
		ConfigurableApplicationContext context = SpringApplication.run(Gh14479Application.class, args);
		YonaProperties yonaProperties = context.getBean(YonaProperties.class);
		System.out.println((yonaProperties.getAnalysisService().getAlpha()));
		System.out.println((yonaProperties.getAnalysisService().getBravo()));
	}

}

@ConfigurationProperties("yona")
class YonaProperties {

	private final AnalysisServiceProperties analysisService = new AnalysisServiceProperties();

	public AnalysisServiceProperties getAnalysisService() {
		return analysisService;
	}

	public class AnalysisServiceProperties {

		private String alpha;

		private String bravo;

		public String getAlpha() {
			return alpha;
		}

		public void setAlpha(String alpha) {
			this.alpha = alpha;
		}

		public String getBravo() {
			return bravo;
		}

		public void setBravo(String bravo) {
			this.bravo = bravo;
		}

	}

}

Run with no properties:

$ java -jar target/gh-14479-0.0.1-SNAPSHOT.jar
…
null
null

Run with an environment variable and a command line property and both take effect:

$ YONA_ANALYSIS_SERVICE_ALPHA=one java -jar target/gh-14479-0.0.1-SNAPSHOT.jar --yona.analysis-service.bravo=two
…
one
two

Run with just a command line property and it takes effect:

$ java -jar target/gh-14479-0.0.1-SNAPSHOT.jar --yona.analysis-service.bravo=two
…
null
two

Run with just an environment variable and it has no effect:

$ YONA_ANALYSIS_SERVICE_ALPHA=one java -jar target/gh-14479-0.0.1-SNAPSHOT.jar
…
null
null

[Bert-R]

That's it indeed. Thanks for making the repro!

[wilkinsona]

When only the environment variable is set, the configuration property name yona.analysis-service is called with yona.analysis.service.alpha and yonaanalysisservicealpha to see if it's an ancestor. In both cases false is returned so it appears that the are no properties to be bound to the AnalysisServiceProperties instance so binding stops.

When the property yona.analysis-service.bravo has been set on the command line in addition to the environment variable, the configuration property name yona.analysis-service is also called with yona.analysis-service.bravo. It correctly determines that it is an ancestor of the passed-in name, so binding continues and both properties are then bound.

[wilkinsona]

The behaviour described above is a symptom of the environment variable not meeting the documented requirements. Specifically, _ should not be used within the name of a property. This means that the environment variable should be named YONA_ANALYSISSERVICE_ALPHA rather than YONA_ANALYSIS_SERVICE_ALPHA. If the former is used, binding works as expected.

I'm going to leave this open for now as the current behaviour is (to me at least) a bit confusing. Ideally, an environment variable that doesn't meet the required guidelines should never bind, irrespective of any other properties that have been configured.

[Bert-R]

That's actually not the case. See the property class implementation here. The property name is camelCased, see application.properties.