docs(tutorials): Call append asynchronously instead of blocking (#1542)

tutorials/JsonWriterDefaultStream/src/main/java/com/example/JsonWriterDefaultStream.java

@@ -17,6 +17,8 @@
 package com.example.bigquerystorage;
 
 import com.google.api.core.ApiFuture;
+import com.google.api.core.ApiFutureCallback;
+import com.google.api.core.ApiFutures;
 import com.google.cloud.bigquery.BigQuery;
 import com.google.cloud.bigquery.BigQueryOptions;
 import com.google.cloud.bigquery.Field;
@@ -31,11 +33,11 @@
 import com.google.cloud.bigquery.storage.v1.JsonStreamWriter;
 import com.google.cloud.bigquery.storage.v1.TableName;
 import com.google.cloud.bigquery.storage.v1.TableSchema;
+import com.google.common.util.concurrent.MoreExecutors;
 import com.google.protobuf.Descriptors.DescriptorValidationException;
 import java.io.BufferedReader;
 import java.io.FileReader;
 import java.io.IOException;
-import java.util.concurrent.ExecutionException;
 import org.json.JSONArray;
 import org.json.JSONObject;
 
@@ -118,20 +120,32 @@ public static void writeToDefaultStream(
           }
         } // batch
         ApiFuture<AppendRowsResponse> future = writer.append(jsonArr);
-        AppendRowsResponse response = future.get();
-        if (response.hasUpdatedSchema()) {
-          // The destination table schema has changed. The client library automatically
-          // reestablishes a connection to the backend using the new schema, so we can continue
-          // to send data without interruption.
-          System.out.println("Table schema changed.");
-        }
+        // The append method is asynchronous. Rather than waiting for the method to complete,
+        // which can hurt performance, register a completion callback and continue streaming.
+        ApiFutures.addCallback(
+            future, new AppendCompleteCallback(), MoreExecutors.directExecutor());
       }
-      System.out.println("Appended records successfully.");
-    } catch (ExecutionException e) {
-      // If the wrapped exception is a StatusRuntimeException, check the state of the operation.
-      // If the state is INTERNAL, CANCELLED, or ABORTED, you can retry. For more information, see:
-      // https://grpc.github.io/grpc-java/javadoc/io/grpc/StatusRuntimeException.html
-      System.out.println("Failed to append records. \n" + e.toString());
     }
   }
 }
+
+class AppendCompleteCallback implements ApiFutureCallback<AppendRowsResponse> {
+
+  private static int batchCount = 0;
+  private static final Object lock = new Object();
+
+  public void onSuccess(AppendRowsResponse response) {
+    synchronized (lock) {
+      if (response.hasError()) {
+        System.out.format("Error: %s\n", response.getError().toString());
+      } else {
+        ++batchCount;
+        System.out.format("Wrote batch %d\n", batchCount);
+      }
+    }
+  }
+
+  public void onFailure(Throwable throwable) {
+    System.out.format("Error: %s\n", throwable.toString());
+  }
+}

tutorials/JsonWriterDefaultStream/src/test/java/com/example/JsonWriterDefaultStreamIT.java

@@ -68,7 +68,7 @@ public void testJsonWriterDefaultStream() throws Exception {
     System.out.println(dataFilePath.toString());
     String[] args = {GOOGLE_CLOUD_PROJECT, datasetName, "github", dataFilePath.toString()};
     JsonWriterDefaultStream.main(args);
-    assertThat(bout.toString()).contains("Appended records successfully.");
+    assertThat(bout.toString()).contains("Wrote batch");
   }
 
   @After