docs(samples): add dataset exists (#492)

Author: Praful Makani

samples/snippets/src/main/java/com/example/bigquery/DatasetExists.java

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+/*
+ * Copyright 2020 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.bigquery;
+
+// [START bigquery_dataset_exists]
+import com.google.cloud.bigquery.BigQuery;
+import com.google.cloud.bigquery.BigQueryException;
+import com.google.cloud.bigquery.BigQueryOptions;
+import com.google.cloud.bigquery.Dataset;
+import com.google.cloud.bigquery.DatasetId;
+
+// Sample to check dataset exist
+public class DatasetExists {
+
+  public static void runDatasetExists() {
+    // TODO(developer): Replace these variables before running the sample.
+    String datasetName = "MY_DATASET_NAME";
+    datasetExists(datasetName);
+  }
+
+  public static void datasetExists(String datasetName) {
+    try {
+      // Initialize client that will be used to send requests. This client only needs to be created
+      // once, and can be reused for multiple requests.
+      BigQuery bigquery = BigQueryOptions.getDefaultInstance().getService();
+
+      Dataset dataset = bigquery.getDataset(DatasetId.of(datasetName));
+      if (dataset.exists()) {
+        System.out.println("Dataset already exist");
+      } else {
+        System.out.println("Dataset not found");
+      }
+    } catch (BigQueryException e) {
+      System.out.println("Dataset not found. \n" + e.toString());
+    }
+  }
+}
+// [END bigquery_dataset_exists]

samples/snippets/src/test/java/com/example/bigquery/DatasetExistsIT.java

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+/*
+ * Copyright 2020 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.bigquery;
+
+import static com.google.common.truth.Truth.assertThat;
+import static junit.framework.TestCase.assertNotNull;
+
+import java.io.ByteArrayOutputStream;
+import java.io.PrintStream;
+import java.util.UUID;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+public class DatasetExistsIT {
+
+  private String datasetName;
+  private ByteArrayOutputStream bout;
+  private PrintStream out;
+
+  private static final String PROJECT_ID = requireEnvVar("GOOGLE_CLOUD_PROJECT");
+
+  private static String requireEnvVar(String varName) {
+    String value = System.getenv(varName);
+    assertNotNull(
+        "Environment variable " + varName + " is required to perform these tests.",
+        System.getenv(varName));
+    return value;
+  }
+
+  @BeforeClass
+  public static void checkRequirements() {
+    requireEnvVar("GOOGLE_CLOUD_PROJECT");
+  }
+
+  @Before
+  public void setUp() {
+    bout = new ByteArrayOutputStream();
+    out = new PrintStream(bout);
+    System.setOut(out);
+    // create a temporary dataset
+    datasetName = "MY_DATASET_TEST_" + UUID.randomUUID().toString().substring(0, 8);
+    CreateDataset.createDataset(datasetName);
+
+    bout = new ByteArrayOutputStream();
+    out = new PrintStream(bout);
+    System.setOut(out);
+  }
+
+  @After
+  public void tearDown() {
+    // delete a temporary dataset
+    DeleteDataset.deleteDataset(PROJECT_ID, datasetName);
+    System.setOut(null);
+  }
+
+  @Test
+  public void testDatasetExists() {
+    DatasetExists.datasetExists(datasetName);
+    assertThat(bout.toString()).contains("Dataset already exist");
+  }
+}