Merge pull request spring-projects#44494 from nosan

* pr/44494:
  Polish "Refine the handling of OpenTelemetry resource attributes"
  Refine the handling of OpenTelemetry resource attributes

Closes spring-projectsgh-44494

Author: mhalbritter

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/export/otlp/OtlpMetricsPropertiesConfigAdapter.java

@@ -17,6 +17,7 @@
 package org.springframework.boot.actuate.autoconfigure.metrics.export.otlp;
 
 import java.util.Collections;
+import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 
@@ -28,7 +29,6 @@
 import org.springframework.boot.actuate.autoconfigure.opentelemetry.OpenTelemetryProperties;
 import org.springframework.boot.actuate.autoconfigure.opentelemetry.OpenTelemetryResourceAttributes;
 import org.springframework.core.env.Environment;
-import org.springframework.util.StringUtils;
 
 /**
  * Adapter to convert {@link OtlpMetricsProperties} to an {@link OtlpConfig}.
@@ -40,11 +40,6 @@
 class OtlpMetricsPropertiesConfigAdapter extends StepRegistryPropertiesConfigAdapter<OtlpMetricsProperties>
 		implements OtlpConfig {
 
-	/**
-	 * Default value for application name if {@code spring.application.name} is not set.
-	 */
-	private static final String DEFAULT_APPLICATION_NAME = "unknown_service";
-
 	private final OpenTelemetryProperties openTelemetryProperties;
 
 	private final OtlpMetricsConnectionDetails connectionDetails;
@@ -77,21 +72,10 @@ public AggregationTemporality aggregationTemporality() {
 
 	@Override
 	public Map<String, String> resourceAttributes() {
-		Map<String, String> attributes = new OpenTelemetryResourceAttributes(
-				this.openTelemetryProperties.getResourceAttributes())
-			.asMap();
-		attributes.computeIfAbsent("service.name", (key) -> getApplicationName());
-		attributes.computeIfAbsent("service.group", (key) -> getApplicationGroup());
-		return Collections.unmodifiableMap(attributes);
-	}
-
-	private String getApplicationName() {
-		return this.environment.getProperty("spring.application.name", DEFAULT_APPLICATION_NAME);
-	}
-
-	private String getApplicationGroup() {
-		String applicationGroup = this.environment.getProperty("spring.application.group");
-		return (StringUtils.hasLength(applicationGroup)) ? applicationGroup : null;
+		Map<String, String> resourceAttributes = new LinkedHashMap<>();
+		new OpenTelemetryResourceAttributes(this.environment, this.openTelemetryProperties.getResourceAttributes())
+			.applyTo(resourceAttributes::put);
+		return Collections.unmodifiableMap(resourceAttributes);
 	}
 
 	@Override

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/opentelemetry/OpenTelemetryAutoConfiguration.java

@@ -16,8 +16,6 @@
 
 package org.springframework.boot.actuate.autoconfigure.opentelemetry;
 
-import java.util.Map;
-
 import io.opentelemetry.api.OpenTelemetry;
 import io.opentelemetry.context.propagation.ContextPropagators;
 import io.opentelemetry.sdk.OpenTelemetrySdk;
@@ -36,7 +34,6 @@
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.context.annotation.Bean;
 import org.springframework.core.env.Environment;
-import org.springframework.util.StringUtils;
 
 /**
  * {@link EnableAutoConfiguration Auto-configuration} for OpenTelemetry.
@@ -49,11 +46,6 @@
 @EnableConfigurationProperties(OpenTelemetryProperties.class)
 public class OpenTelemetryAutoConfiguration {
 
-	/**
-	 * Default value for application name if {@code spring.application.name} is not set.
-	 */
-	private static final String DEFAULT_APPLICATION_NAME = "unknown_service";
-
 	@Bean
 	@ConditionalOnMissingBean(OpenTelemetry.class)
 	OpenTelemetrySdk openTelemetry(ObjectProvider<SdkTracerProvider> tracerProvider,
@@ -76,21 +68,8 @@ Resource openTelemetryResource(Environment environment, OpenTelemetryProperties
 
 	private Resource toResource(Environment environment, OpenTelemetryProperties properties) {
 		ResourceBuilder builder = Resource.builder();
-		Map<String, String> attributes = new OpenTelemetryResourceAttributes(properties.getResourceAttributes())
-			.asMap();
-		attributes.computeIfAbsent("service.name", (key) -> getApplicationName(environment));
-		attributes.computeIfAbsent("service.group", (key) -> getApplicationGroup(environment));
-		attributes.forEach(builder::put);
+		new OpenTelemetryResourceAttributes(environment, properties.getResourceAttributes()).applyTo(builder::put);
 		return builder.build();
 	}
 
-	private String getApplicationName(Environment environment) {
-		return environment.getProperty("spring.application.name", DEFAULT_APPLICATION_NAME);
-	}
-
-	private String getApplicationGroup(Environment environment) {
-		String applicationGroup = environment.getProperty("spring.application.group");
-		return (StringUtils.hasLength(applicationGroup)) ? applicationGroup : null;
-	}
-
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/opentelemetry/OpenTelemetryResourceAttributes.java

@@ -21,16 +21,19 @@
 import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.Map;
+import java.util.function.BiConsumer;
 import java.util.function.Function;
 
+import org.springframework.core.env.Environment;
+import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 
 /**
- * OpenTelemetryResourceAttributes retrieves information from the
+ * {@link OpenTelemetryResourceAttributes} retrieves information from the
  * {@code OTEL_RESOURCE_ATTRIBUTES} and {@code OTEL_SERVICE_NAME} environment variables
- * and merges it with the resource attributes provided by the user.
- * <p>
- * <b>User-provided resource attributes take precedence.</b>
+ * and merges it with the resource attributes provided by the user. User-provided resource
+ * attributes take precedence. Additionally, {@code spring.application.*} related
+ * properties can be applied as defaults.
  * <p>
  * <a href= "https://opentelemetry.io/docs/specs/otel/resource/sdk/">OpenTelemetry
  * Resource Specification</a>
@@ -40,47 +43,72 @@
  */
 public final class OpenTelemetryResourceAttributes {
 
+	/**
+	 * Default value for service name if {@code service.name} is not set.
+	 */
+	private static final String DEFAULT_SERVICE_NAME = "unknown_service";
+
+	private final Environment environment;
+
 	private final Map<String, String> resourceAttributes;
 
 	private final Function<String, String> getEnv;
 
 	/**
 	 * Creates a new instance of {@link OpenTelemetryResourceAttributes}.
+	 * @param environment the environment
 	 * @param resourceAttributes user provided resource attributes to be used
 	 */
-	public OpenTelemetryResourceAttributes(Map<String, String> resourceAttributes) {
-		this(resourceAttributes, null);
+	public OpenTelemetryResourceAttributes(Environment environment, Map<String, String> resourceAttributes) {
+		this(environment, resourceAttributes, null);
 	}
 
 	/**
 	 * Creates a new {@link OpenTelemetryResourceAttributes} instance.
+	 * @param environment the environment
 	 * @param resourceAttributes user provided resource attributes to be used
 	 * @param getEnv a function to retrieve environment variables by name
 	 */
-	OpenTelemetryResourceAttributes(Map<String, String> resourceAttributes, Function<String, String> getEnv) {
+	OpenTelemetryResourceAttributes(Environment environment, Map<String, String> resourceAttributes,
+			Function<String, String> getEnv) {
+		Assert.notNull(environment, "'environment' must not be null");
+		this.environment = environment;
 		this.resourceAttributes = (resourceAttributes != null) ? resourceAttributes : Collections.emptyMap();
 		this.getEnv = (getEnv != null) ? getEnv : System::getenv;
 	}
 
 	/**
-	 * Returns resource attributes by combining attributes from environment variables and
-	 * user-defined resource attributes. The final resource contains all attributes from
-	 * both sources.
+	 * Applies resource attributes to the provided BiConsumer after being combined from
+	 * environment variables and user-defined resource attributes.
 	 * <p>
 	 * If a key exists in both environment variables and user-defined resources, the value
 	 * from the user-defined resource takes precedence, even if it is empty.
 	 * <p>
-	 * <b>Null keys and values are ignored.</b>
-	 * @return the resource attributes
+	 * Additionally, {@code spring.application.name} or {@code unknown_service} will be
+	 * used as the default for {@code service.name}, and {@code spring.application.group}
+	 * will serve as the default for {@code service.group}.
+	 * @param consumer the {@link BiConsumer} to apply
 	 */
-	public Map<String, String> asMap() {
+	public void applyTo(BiConsumer<String, String> consumer) {
+		Assert.notNull(consumer, "'consumer' must not be null");
 		Map<String, String> attributes = getResourceAttributesFromEnv();
 		this.resourceAttributes.forEach((name, value) -> {
-			if (name != null && value != null) {
+			if (StringUtils.hasLength(name) && value != null) {
 				attributes.put(name, value);
 			}
 		});
-		return attributes;
+		attributes.computeIfAbsent("service.name", (k) -> getApplicationName());
+		attributes.computeIfAbsent("service.group", (k) -> getApplicationGroup());
+		attributes.forEach(consumer);
+	}
+
+	private String getApplicationName() {
+		return this.environment.getProperty("spring.application.name", DEFAULT_SERVICE_NAME);
+	}
+
+	private String getApplicationGroup() {
+		String applicationGroup = this.environment.getProperty("spring.application.group");
+		return (StringUtils.hasLength(applicationGroup)) ? applicationGroup : null;
 	}
 
 	/**
@@ -122,7 +150,7 @@ private String getEnv(String name) {
 	 * @param value value to decode
 	 * @return the decoded string
 	 */
-	public static String decode(String value) {
+	private static String decode(String value) {
 		if (value.indexOf('%') < 0) {
 			return value;
 		}