Fix Scheduled observation convention for lambdas

Prior to this commit, the `DefaultScheduledTaskObservationConvention`
would fail as it tried to add a `KeyValue` to the observation context
that is `null`. This is rejected by the observation registry and should
be prevented. This happened when registered scheduled methods were
lambdas or part of anonymous classes. Those types do not have a
canonical name and return `null` as a value there.

This commit ensures that for these cases, the default convetion uses a
`"ANONYMOUS"` value as the `"code.namespace"` keyvalue.

Fixes gh-31918

framework-docs/modules/ROOT/pages/integration/observability.adoc

@@ -108,7 +108,7 @@ By default, the following `KeyValues` are created:
 |===
 |Name | Description
 |`code.function` _(required)_|Name of Java `Method` that is scheduled for execution.
-|`code.namespace` _(required)_|Canonical name of the class of the bean instance that holds the scheduled method.
+|`code.namespace` _(required)_|Canonical name of the class of the bean instance that holds the scheduled method, or `"ANONYMOUS"` for anonymous classes.
 |`error` _(required)_|Class name of the exception thrown during the execution, or `"none"` if no exception happened.
 |`exception` _(deprecated)_|Duplicates the `error` key and might be removed in the future.
 |`outcome` _(required)_|Outcome of the method execution. Can be `"SUCCESS"`, `"ERROR"` or `"UNKNOWN"` (if for example the operation was cancelled during execution).

spring-context/src/main/java/org/springframework/scheduling/support/DefaultScheduledTaskObservationConvention.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -40,6 +40,8 @@ public class DefaultScheduledTaskObservationConvention implements ScheduledTaskO
 
 	private static final KeyValue OUTCOME_UNKNOWN = KeyValue.of(LowCardinalityKeyNames.OUTCOME, "UNKNOWN");
 
+	private static final KeyValue CODE_NAMESPACE_ANONYMOUS = KeyValue.of(LowCardinalityKeyNames.CODE_NAMESPACE, "ANONYMOUS");
+
 	@Override
 	public String getName() {
 		return DEFAULT_NAME;
@@ -61,7 +63,10 @@ protected KeyValue codeFunction(ScheduledTaskObservationContext context) {
 	}
 
 	protected KeyValue codeNamespace(ScheduledTaskObservationContext context) {
-		return KeyValue.of(LowCardinalityKeyNames.CODE_NAMESPACE, context.getTargetClass().getCanonicalName());
+		if (context.getTargetClass().getCanonicalName() != null) {
+			return KeyValue.of(LowCardinalityKeyNames.CODE_NAMESPACE, context.getTargetClass().getCanonicalName());
+		}
+		return CODE_NAMESPACE_ANONYMOUS;
 	}
 
 	protected KeyValue exception(ScheduledTaskObservationContext context) {

spring-context/src/test/java/org/springframework/scheduling/support/DefaultScheduledTaskObservationConventionTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -35,6 +35,8 @@ class DefaultScheduledTaskObservationConventionTests {
 
 	private final Method taskMethod = ClassUtils.getMethod(BeanWithScheduledMethods.class, "process");
 
+	private final Method runMethod = ClassUtils.getMethod(Runnable.class, "run");
+
 	private final ScheduledTaskObservationConvention convention = new DefaultScheduledTaskObservationConvention();
 
 
@@ -69,6 +71,21 @@ void observationShouldHaveMethodName() {
 		assertThat(convention.getLowCardinalityKeyValues(context)).contains(KeyValue.of("code.function", "process"));
 	}
 
+	@Test
+	void observationShouldHaveTargetTypeForAnonymousClass() {
+		Runnable runnable = () -> { };
+		ScheduledTaskObservationContext context = new ScheduledTaskObservationContext(runnable, runMethod);
+		assertThat(convention.getLowCardinalityKeyValues(context))
+				.contains(KeyValue.of("code.namespace", "ANONYMOUS"));
+	}
+
+	@Test
+	void observationShouldHaveMethodNameForAnonymousClass() {
+		Runnable runnable = () -> { };
+		ScheduledTaskObservationContext context = new ScheduledTaskObservationContext(runnable, runMethod);
+		assertThat(convention.getLowCardinalityKeyValues(context)).contains(KeyValue.of("code.function", "run"));
+	}
+
 	@Test
 	void observationShouldHaveSuccessfulOutcome() {
 		ScheduledTaskObservationContext context = new ScheduledTaskObservationContext(new BeanWithScheduledMethods(), taskMethod);