Add demo baggage span processor

* this shows how to inject baggage attributes to a span

Co-authored-by: MarianaSequeira <mfs98@live.com.pt>

examples/extension/README.md

@@ -39,6 +39,7 @@ For more information, see the `extendedAgent` task in [build.gradle](build.gradl
 [DemoPropagator]: src/main/java/com/example/javaagent/DemoPropagator.java
 [DemoSampler]: src/main/java/com/example/javaagent/DemoSampler.java
 [DemoSpanProcessor]: src/main/java/com/example/javaagent/DemoSpanProcessor.java
+[DemoBaggageSpanProcessor]: src/main/java/com/example/javaagent/DemoBaggageSpanProcessor.java
 [DemoSpanExporter]: src/main/java/com/example/javaagent/DemoSpanExporter.java
 [DemoServlet3InstrumentationModule]: src/main/java/com/example/javaagent/instrumentation/DemoServlet3InstrumentationModule.java
 
@@ -47,6 +48,7 @@ For more information, see the `extendedAgent` task in [build.gradle](build.gradl
 - Custom `TextMapPropagator`: [DemoPropagator][DemoPropagator]
 - Custom `Sampler`: [DemoSampler][DemoSampler]
 - Custom `SpanProcessor`: [DemoSpanProcessor][DemoSpanProcessor]
+- Custom `SpanProcessor`: [DemoBaggageSpanProcessor][DemoBaggageSpanProcessor]
 - Custom `SpanExporter`: [DemoSpanExporter][DemoSpanExporter]
 - Additional instrumentation: [DemoServlet3InstrumentationModule][DemoServlet3InstrumentationModule]
 

examples/extension/src/main/java/com/example/javaagent/DemoAutoConfigurationCustomizerProvider.java

@@ -43,6 +43,7 @@ private SdkTracerProviderBuilder configureSdkTracerProvider(
         .setIdGenerator(new DemoIdGenerator())
         .setSpanLimits(SpanLimits.builder().setMaxNumberOfAttributes(1024).build())
         .addSpanProcessor(new DemoSpanProcessor())
+        .addSpanProcessor(new DemoBaggageSpanProcessor())
         .addSpanProcessor(SimpleSpanProcessor.create(new DemoSpanExporter()));
   }
 

examples/extension/src/main/java/com/example/javaagent/DemoBaggageSpanProcessor.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.example.javaagent;
+
+import io.opentelemetry.api.baggage.Baggage;
+import io.opentelemetry.context.Context;
+import io.opentelemetry.sdk.trace.ReadWriteSpan;
+import io.opentelemetry.sdk.trace.ReadableSpan;
+import io.opentelemetry.sdk.trace.SpanProcessor;
+
+/**
+ * Custom Span Processor to inject Baggage attributes to a Span. This allows to use the Baggage to
+ * hold some custom values and inject them automatically into the child Spans.
+ *
+ * <p>See <a
+ * href="https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/trace/sdk.md#span-processor">
+ * OpenTelemetry Specification</a> for more information about {@link SpanProcessor}.
+ *
+ * @see DemoAutoConfigurationCustomizerProvider
+ */
+public class DemoBaggageSpanProcessor implements SpanProcessor {
+
+  @Override
+  public void onStart(Context parentContext, ReadWriteSpan span) {
+    Baggage.fromContext(parentContext)
+        .forEach((s, baggageEntry) -> span.setAttribute(s, baggageEntry.getValue()));
+  }
+
+  @Override
+  public boolean isStartRequired() {
+    return true;
+  }
+
+  @Override
+  public void onEnd(ReadableSpan span) {
+    // Do nothing on span end
+  }
+
+  @Override
+  public boolean isEndRequired() {
+    return false;
+  }
+}