Allow for simpler creation of start-only and end-only SpanProcessors.

sdk-extensions/autoconfigure/src/testFullConfig/java/io/opentelemetry/sdk/autoconfigure/provider/TestTracerProviderConfigurer.java

@@ -5,37 +5,18 @@
 
 package io.opentelemetry.sdk.autoconfigure.provider;
 
-import io.opentelemetry.context.Context;
 import io.opentelemetry.sdk.autoconfigure.spi.ConfigProperties;
-import io.opentelemetry.sdk.trace.ReadWriteSpan;
-import io.opentelemetry.sdk.trace.ReadableSpan;
+import io.opentelemetry.sdk.extension.incubator.trace.OnStartSpanProcessor;
 import io.opentelemetry.sdk.trace.SdkTracerProviderBuilder;
-import io.opentelemetry.sdk.trace.SpanProcessor;
 
 @SuppressWarnings("deprecation") // Support testing of SdkTracerProviderConfigurer
 public class TestTracerProviderConfigurer
     implements io.opentelemetry.sdk.autoconfigure.spi.traces.SdkTracerProviderConfigurer {
   @Override
   public void configure(SdkTracerProviderBuilder tracerProvider, ConfigProperties config) {
     tracerProvider.addSpanProcessor(
-        new SpanProcessor() {
-          @Override
-          public void onStart(Context parentContext, ReadWriteSpan span) {
-            span.setAttribute("configured", config.getBoolean("otel.test.configured"));
-          }
-
-          @Override
-          public boolean isStartRequired() {
-            return true;
-          }
-
-          @Override
-          public void onEnd(ReadableSpan span) {}
-
-          @Override
-          public boolean isEndRequired() {
-            return false;
-          }
-        });
+        OnStartSpanProcessor.create(
+            (ctx, span) ->
+                span.setAttribute("configured", config.getBoolean("otel.test.configured"))));
   }
 }

sdk-extensions/incubator/src/main/java/io/opentelemetry/sdk/extension/incubator/trace/OnEndSpanProcessor.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.extension.incubator.trace;
+
+import io.opentelemetry.context.Context;
+import io.opentelemetry.sdk.trace.ReadWriteSpan;
+import io.opentelemetry.sdk.trace.ReadableSpan;
+import io.opentelemetry.sdk.trace.SpanProcessor;
+
+/** A SpanProcessor implementation that is only capable of processing spans when they end. */
+public final class OnEndSpanProcessor implements SpanProcessor {
+  private final OnEnd onEnd;
+
+  private OnEndSpanProcessor(OnEnd onEnd) {
+    this.onEnd = onEnd;
+  }
+
+  static SpanProcessor create(OnEnd onEnd) {
+    return new OnEndSpanProcessor(onEnd);
+  }
+
+  @Override
+  public void onEnd(ReadableSpan span) {
+    onEnd.apply(span);
+  }
+
+  @Override
+  public boolean isEndRequired() {
+    return true;
+  }
+
+  @Override
+  public void onStart(Context parentContext, ReadWriteSpan span) {
+    // nop
+  }
+
+  @Override
+  public boolean isStartRequired() {
+    return false;
+  }
+
+  @FunctionalInterface
+  public interface OnEnd {
+    void apply(ReadableSpan span);
+  }
+}

sdk-extensions/incubator/src/main/java/io/opentelemetry/sdk/extension/incubator/trace/OnStartSpanProcessor.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.extension.incubator.trace;
+
+import io.opentelemetry.context.Context;
+import io.opentelemetry.sdk.trace.ReadWriteSpan;
+import io.opentelemetry.sdk.trace.ReadableSpan;
+import io.opentelemetry.sdk.trace.SpanProcessor;
+
+/** A SpanProcessor that only handles onStart(). */
+public final class OnStartSpanProcessor implements SpanProcessor {
+
+  private final OnStart onStart;
+
+  private OnStartSpanProcessor(OnStart onStart) {
+    this.onStart = onStart;
+  }
+
+  public static SpanProcessor create(OnStart onStart) {
+    return new OnStartSpanProcessor(onStart);
+  }
+
+  @Override
+  public void onStart(Context parentContext, ReadWriteSpan span) {
+    onStart.apply(parentContext, span);
+  }
+
+  @Override
+  public boolean isStartRequired() {
+    return true;
+  }
+
+  @Override
+  public void onEnd(ReadableSpan span) {
+    // nop
+  }
+
+  @Override
+  public boolean isEndRequired() {
+    return false;
+  }
+
+  @FunctionalInterface
+  public interface OnStart {
+    void apply(Context context, ReadWriteSpan span);
+  }
+}

sdk-extensions/incubator/src/test/java/io/opentelemetry/sdk/extension/incubator/trace/OnEndSpanProcessorTest.java

@@ -0,0 +1,31 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.extension.incubator.trace;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+
+import io.opentelemetry.sdk.trace.ReadWriteSpan;
+import io.opentelemetry.sdk.trace.ReadableSpan;
+import io.opentelemetry.sdk.trace.SpanProcessor;
+import java.util.concurrent.atomic.AtomicReference;
+import org.junit.jupiter.api.Test;
+
+class OnEndSpanProcessorTest {
+
+  @Test
+  void endOnly() {
+    AtomicReference<ReadableSpan> seenSpan = new AtomicReference<>();
+    ReadWriteSpan inputSpan = mock(ReadWriteSpan.class);
+
+    SpanProcessor processor = OnEndSpanProcessor.create(seenSpan::set);
+
+    assertThat(processor.isStartRequired()).isFalse();
+    assertThat(processor.isEndRequired()).isTrue();
+    processor.onEnd(inputSpan);
+    assertThat(seenSpan.get()).isSameAs(inputSpan);
+  }
+}

sdk-extensions/incubator/src/test/java/io/opentelemetry/sdk/extension/incubator/trace/OnStartSpanProcessorTest.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.extension.incubator.trace;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+
+import io.opentelemetry.context.Context;
+import io.opentelemetry.sdk.trace.ReadWriteSpan;
+import io.opentelemetry.sdk.trace.SpanProcessor;
+import java.util.concurrent.atomic.AtomicReference;
+import org.junit.jupiter.api.Test;
+
+class OnStartSpanProcessorTest {
+
+  @Test
+  void startOnly() {
+    AtomicReference<Context> seenContext = new AtomicReference<>();
+    AtomicReference<ReadWriteSpan> seenSpan = new AtomicReference<>();
+    Context context = mock(Context.class);
+    ReadWriteSpan inputSpan = mock(ReadWriteSpan.class);
+
+    SpanProcessor processor =
+        OnStartSpanProcessor.create(
+            (ctx, span) -> {
+              seenContext.set(ctx);
+              seenSpan.set(span);
+            });
+
+    assertThat(processor.isStartRequired()).isTrue();
+    assertThat(processor.isEndRequired()).isFalse();
+    processor.onStart(context, inputSpan);
+    assertThat(seenContext.get()).isSameAs(context);
+    assertThat(seenSpan.get()).isSameAs(inputSpan);
+  }
+}