Add "createNotStarted" method that lazily creates context

micrometer-observation/src/main/java/io/micrometer/observation/docs/DocumentedObservation.java

@@ -19,11 +19,13 @@
 import io.micrometer.common.lang.NonNull;
 import io.micrometer.common.lang.Nullable;
 import io.micrometer.observation.Observation;
+import io.micrometer.observation.ObservationPredicate;
 import io.micrometer.observation.ObservationRegistry;
 import io.micrometer.observation.GlobalObservationConvention;
 import io.micrometer.observation.ObservationConvention;
 
 import java.util.Objects;
+import java.util.function.Supplier;
 
 /**
  * In order to describe your samples via e.g. enums instead of Strings you can use this
@@ -187,6 +189,32 @@ default <T extends Observation.Context> Observation observation(@Nullable Observ
         return observation;
     }
 
+    /**
+     * Creates an {@link Observation} for the given {@link ObservationConvention}. You
+     * need to manually start it. When the {@link ObservationRegistry} is a no-op, this
+     * method fast returns a no-op {@link Observation} and skips the creation of the
+     * {@link Observation.Context}. This quick check avoids unnecessary
+     * {@link Observation.Context} creations. More detailed check, such as
+     * {@link ObservationPredicate}, is performed at the later stage after
+     * {@link Observation.Context} creation.
+     * @param customConvention convention that (if not {@code null}) will override any
+     * pre-configured conventions
+     * @param defaultConvention default convention that will be picked if there was
+     * neither custom convention nor a pre-configured one via
+     * {@link ObservationRegistry.ObservationConfig#observationConvention(GlobalObservationConvention[])}
+     * @param contextSupplier observation context supplier
+     * @param registry observation registry
+     * @return observation
+     */
+    default <T extends Observation.Context> Observation createNotStarted(
+            @Nullable ObservationConvention<T> customConvention, @NonNull ObservationConvention<T> defaultConvention,
+            @NonNull Supplier<T> contextSupplier, @NonNull ObservationRegistry registry) {
+        if (registry.isNoop()) {
+            return Observation.NOOP;
+        }
+        return observation(customConvention, defaultConvention, contextSupplier.get(), registry);
+    }
+
     /**
      * Creates and starts an {@link Observation}.
      * @param registry observation registry

micrometer-observation/src/test/java/io/micrometer/observation/docs/DocumentedObservationTests.java

@@ -15,9 +15,13 @@
  */
 package io.micrometer.observation.docs;
 
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.function.Supplier;
+
 import io.micrometer.common.KeyValue;
 import io.micrometer.common.KeyValues;
 import io.micrometer.observation.Observation;
+import io.micrometer.observation.Observation.Context;
 import io.micrometer.observation.ObservationFilter;
 import io.micrometer.observation.ObservationRegistry;
 import io.micrometer.observation.GlobalObservationConvention;
@@ -116,6 +120,22 @@ void keyValuesShouldBeAlwaysAdded() {
         assertThat(context.getHighCardinalityKeyValues()).containsOnly(KeyValue.of("global", "high cardinality"));
     }
 
+    @Test
+    void createNotStartedShouldNotCreateContextWithNoopRegistry() {
+        ObservationRegistry registry = ObservationRegistry.NOOP;
+
+        AtomicBoolean isCalled = new AtomicBoolean();
+        Supplier<Context> supplier = () -> {
+            isCalled.set(true);
+            return new Observation.Context();
+        };
+
+        Observation observation = TestConventionObservation.CONTEXTUAL_NAME.createNotStarted(null,
+                new FirstObservationConvention(), supplier, registry);
+        assertThat(observation.isNoop()).isTrue();
+        assertThat(isCalled).isFalse();
+    }
+
     private ObservationRegistry observationRegistry() {
         ObservationRegistry registry = ObservationRegistry.create();
         registry.observationConfig().observationHandler(context -> true);