docs(sample): Update the subscribe with error listener and subscribe with exactly-once samples (#2437)

* docs(sample): Update SubscribeWithErrorListener sample to not rebuild the subscriber

* docs(sample): Add locational endpoint for exactly-once subscriber sample

* docs(sample): Add comment explaining reasoning for locational endpoint

Author: michaelpri10

samples/snippets/src/main/java/pubsub/SubscribeWithErrorListenerExample.java

@@ -62,15 +62,11 @@ public static void subscribeWithErrorListenerExample(String projectId, String su
               .setExecutorProvider(executorProvider)
               .build();
 
-      // Listen for unrecoverable failures. Rebuild a subscriber and restart subscribing
-      // when the current subscriber encounters permanent errors.
+      // Listen for unrecoverable failures.
       subscriber.addListener(
           new Subscriber.Listener() {
             public void failed(Subscriber.State from, Throwable failure) {
-              System.out.println(failure.getStackTrace());
-              if (!executorProvider.getExecutor().isShutdown()) {
-                subscribeWithErrorListenerExample(projectId, subscriptionId);
-              }
+              System.out.println("Unrecoverable subscriber failure:" + failure.getStackTrace());
             }
           },
           MoreExecutors.directExecutor());

samples/snippets/src/main/java/pubsub/SubscribeWithExactlyOnceConsumerWithResponseExample.java

@@ -95,7 +95,14 @@ public static void subscribeWithExactlyOnceConsumerWithResponseExample(
 
     Subscriber subscriber = null;
     try {
-      subscriber = Subscriber.newBuilder(subscriptionName, receiverWithResponse).build();
+      // Pub/Sub's exactly once delivery guarantee only applies when subscribers connect to the
+      // service in the same region.
+      // For list of locational endpoints for Pub/Sub, see
+      // https://cloud.google.com/pubsub/docs/reference/service_apis_overview#list_of_locational_endpoints
+      subscriber =
+          Subscriber.newBuilder(subscriptionName, receiverWithResponse)
+              .setEndpoint("us-west1-pubsub.googleapis.com:443")
+              .build();
       // Start the subscriber.
       subscriber.startAsync().awaitRunning();
       System.out.printf("Listening for messages on %s:\n", subscriptionName.toString());