Modify the pubsub example to have custom span.

examples/src/main/java/io/dapr/examples/pubsub/http/PublisherWithTracing.java

@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) Microsoft Corporation and Dapr Contributors.
+ * Licensed under the MIT License.
+ */
+
+package io.dapr.examples.pubsub.http;
+
+import io.dapr.client.DaprClient;
+import io.dapr.client.DaprClientBuilder;
+import io.dapr.examples.OpenTelemetryConfig;
+import io.opentelemetry.api.OpenTelemetry;
+import io.opentelemetry.api.trace.Span;
+import io.opentelemetry.api.trace.Tracer;
+import io.opentelemetry.context.Scope;
+import io.opentelemetry.sdk.OpenTelemetrySdk;
+
+import static io.dapr.examples.OpenTelemetryConfig.getReactorContext;
+
+/**
+ * Message publisher.
+ * 1. Build and install jars:
+ * mvn clean install
+ * 2. cd [repo root]/examples
+ * 3. Run the program:
+ * dapr run --components-path ./components/pubsub --app-id publisher_tracing -- \
+ * java -jar target/dapr-java-sdk-examples-exec.jar io.dapr.examples.pubsub.http.PublisherWithTracing
+ */
+public class PublisherWithTracing {
+
+  //Number of messages to be sent.
+  private static final int NUM_MESSAGES = 10;
+
+  //The title of the topic to be used for publishing
+  private static final String TOPIC_NAME = "testingtopic";
+
+  //The name of the pubsub
+  private static final String PUBSUB_NAME = "messagebus";
+
+  /**
+   * This is the entry point of the publisher app example.
+   *
+   * @param args Args, unused.
+   * @throws Exception A startup Exception.
+   */
+  public static void main(String[] args) throws Exception {
+    OpenTelemetry openTelemetry = OpenTelemetryConfig.createOpenTelemetry();
+    Tracer tracer = openTelemetry.getTracer(PublisherWithTracing.class.getCanonicalName());
+    Span span = tracer.spanBuilder("Publisher's Main").setSpanKind(Span.Kind.CLIENT).startSpan();
+
+    try (DaprClient client = new DaprClientBuilder().build()) {
+      try (Scope scope = span.makeCurrent()) {
+        for (int i = 0; i < NUM_MESSAGES; i++) {
+          String message = String.format("This is message #%d", i);
+          // Publishing messages, notice the use of subscriberContext() for tracing.
+          client.publishEvent(
+              PUBSUB_NAME,
+              TOPIC_NAME,
+              message).subscriberContext(getReactorContext()).block();
+          System.out.println("Published message: " + message);
+
+          try {
+            Thread.sleep((long) (1000 * Math.random()));
+          } catch (InterruptedException e) {
+            e.printStackTrace();
+            Thread.currentThread().interrupt();
+            return;
+          }
+        }
+      }
+
+      // Close the span.
+      span.end();
+
+      // Shutdown the OpenTelemetry tracer.
+      OpenTelemetrySdk.getGlobalTracerManagement().shutdown();
+
+      // This is an example, so for simplicity we are just exiting here.
+      // Normally a dapr app would be a web service and not exit main.
+      System.out.println("Done.");
+    }
+  }
+}

examples/src/main/java/io/dapr/examples/pubsub/http/README.md

@@ -238,6 +238,41 @@ Once running, the Subscriber should print the output as follows:
 
 Messages have been retrieved from the topic.
 
+### Tracing
+
+Dapr handles tracing in PubSub automatically. Open Zipkin on [http://localhost:9411/zipkin](http://localhost:9411/zipkin). You should see a screen like the one below:
+
+![zipking-landing](https://raw.githubusercontent.com/dapr/java-sdk/master/examples/src/main/resources/img/zipkin-pubsub-landing.png)
+
+Click on the search icon to see the latest query results. You should see a tracing diagram similar to the one below:
+
+![zipking-landing](https://raw.githubusercontent.com/dapr/java-sdk/master/examples/src/main/resources/img/zipkin-pubsub-result.png)
+
+Once you click on the tracing event, you will see the details of the call stack starting in the client and then showing the service API calls right below.
+
+![zipking-details](https://raw.githubusercontent.com/dapr/java-sdk/master/examples/src/main/resources/img/zipkin-pubsub-details.png)
+
+If you would like to add a tracing span as a parent of the span created by Dapr, change the publisher to handle that. See `PublisherWithTracing.java` to see the difference and run it with:
+
+<!-- STEP
+name: Run Publisher
+expected_stdout_lines:
+  - '== APP == Published message: This is message #0'
+  - '== APP == Published message: This is message #1'
+background: true
+sleep: 15
+-->
+
+```bash
+dapr run --components-path ./components/pubsub --app-id publisher_tracing -- java -jar target/dapr-java-sdk-examples-exec.jar io.dapr.examples.pubsub.http.PublisherWithTracing
+```
+
+<!-- END_STEP -->
+
+Now, repeat the search on Zipkin website. All the publisher and subscriber spans are under the same parent span, like in the screen below:
+
+![zipking-details-custom-span](https://raw.githubusercontent.com/dapr/java-sdk/master/examples/src/main/resources/img/zipkin-pubsub-details-custom-span.png)
+
 ### Message expiration (Optional)
 
 Optionally, you can see how Dapr can automatically drop expired messages on behalf of the subscriber.