Adding Dataflow MDC Sample (#10204)

* Adding Dataflow MDC Sample

* Update dataflow/snippets/src/main/java/com/example/dataflow/MdcSample.java

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* Update dataflow/snippets/src/main/java/com/example/dataflow/MdcSample.java

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* Update dataflow/snippets/src/main/java/com/example/dataflow/MdcSample.java

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* fixing imports

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: ebeltran-g

dataflow/snippets/src/main/java/com/example/dataflow/MdcSample.java

@@ -0,0 +1,83 @@
+/*
+ * Copyright 2025 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.dataflow;
+
+import org.apache.beam.sdk.Pipeline;
+import org.apache.beam.sdk.io.gcp.pubsub.PubsubIO;
+import org.apache.beam.sdk.io.gcp.pubsub.PubsubMessage;
+import org.apache.beam.sdk.options.Description;
+import org.apache.beam.sdk.options.PipelineOptionsFactory;
+import org.apache.beam.sdk.options.SdkHarnessOptions;
+import org.apache.beam.sdk.transforms.DoFn;
+import org.apache.beam.sdk.transforms.ParDo;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.slf4j.MDC;
+
+public class MdcSample {
+
+  public interface MdcSampleJobOptions extends SdkHarnessOptions {
+    @Description("The Pub/Sub subscription to read from.")
+    String getInputSubscription();
+
+    void setInputSubscription(String value);
+  }
+
+  public static class MessageReaderFn extends DoFn<PubsubMessage, Void> {
+
+    private transient Logger logger;
+
+    @Setup
+    public void setup() {
+      logger = LoggerFactory.getLogger(MessageReaderFn.class);
+    }
+
+    @ProcessElement
+    public void processElement(ProcessContext c) {
+      PubsubMessage message = c.element();
+      String messageId = message.getMessageId();
+
+      try (MDC.MDCCloseable ignored = MDC.putCloseable("messageId", messageId)) {
+        String payload = new String(message.getPayload(), java.nio.charset.StandardCharsets.UTF_8);
+        logger.info("Received message with payload: {}", payload);
+
+        // This is the example task
+        logger.info("Executing example task...");
+      } catch (Exception e) {
+        logger.error("Failed to process message", e);
+      }
+    }
+  }
+
+  public static void main(String[] args) {
+    MdcSampleJobOptions options =
+        PipelineOptionsFactory.fromArgs(args).withValidation().as(MdcSampleJobOptions.class);
+    // options.setRunner(DirectRunner.class);
+
+    options.setLogMdc(true);
+
+
+    Pipeline p = Pipeline.create(options);
+
+    p.apply(
+            "Read Messages from Pub/Sub",
+            PubsubIO.readMessagesWithAttributes().fromSubscription(options.getInputSubscription()))
+        .apply("Process Message", ParDo.of(new MessageReaderFn()));
+
+    p.run();
+  }
+}