samples: add samples for tagging feature

samples/snippets/src/main/java/com/example/spanner/TransactionWithTagSample.java

@@ -0,0 +1,92 @@
+/*
+ * Copyright 2021 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.spanner;
+
+import com.google.cloud.spanner.DatabaseClient;
+import com.google.cloud.spanner.Options;
+import com.google.cloud.spanner.ResultSet;
+import com.google.cloud.spanner.Statement;
+import com.google.cloud.spanner.TransactionContext;
+import com.google.cloud.spanner.TransactionRunner.TransactionCallable;
+
+/**
+ * Sample showing how to add and query tags to Cloud Spanner operations.
+ */
+public class TransactionWithTagSample {
+
+  // [START spanner_set_transaction_tag]
+  static void setTransactionTag(DatabaseClient databaseClient) {
+    // Sets the transaction tag to "app=concert,env=dev".
+    // This transaction tag will be applied to all the individual operations inside this
+    // transaction.
+    databaseClient
+        .readWriteTransaction(Options.tag("app=concert,env=dev"))
+        .run(
+            new TransactionCallable<Void>() {
+              @Override
+              public Void run(TransactionContext transaction) throws Exception {
+                Statement selectStatement = Statement.newBuilder(
+                    "SELECT VenueId, VenueName, Capacity FROM Venues "
+                        + "WHERE OutdoorVenue = @outdoorVenue")
+                    .bind("outdoorVenue")
+                    .to(false)
+                    .build();
+
+                // Sets the request tag to "app=concert,env=dev,action=select".
+                // This request tag will only be set on this request.
+                ResultSet resultSet = transaction.executeQuery(
+                    selectStatement, Options.tag("app=concert,env=dev,action=select"));
+
+                while (resultSet.next()) {
+                  long newCapacity = resultSet.getLong(2) / 4;
+                  Statement updateStatement = Statement.newBuilder(
+                      "UPDATE Venues SET Capacity = @capacity WHERE VenueId = @venueId")
+                      .bind("capacity")
+                      .to(newCapacity)
+                      .bind("venueId")
+                      .to(resultSet.getLong(0))
+                      .build();
+
+                  // Sets the request tag to "app=concert,env=dev,action=update".
+                  // This request tag will only be set on this request.
+                  transaction.executeUpdate(
+                      updateStatement, Options.tag("app=concert,env=dev,action=update"));
+                  System.out.printf(
+                      "Capacity of %s updated to %d\n", resultSet.getString(1), newCapacity);
+                }
+
+                return null;
+              }
+            });
+  }
+  // [END spanner_set_transaction_tag]
+
+  // [START spanner_set_request_tag]
+  static void setRequestTag(DatabaseClient databaseClient) {
+    // Sets the request tag to "app=concert,env=dev,action=select".
+    // This request tag will only be set on this request.
+    try (ResultSet resultSet = dbClient.singleUse().executeQuery(
+        Statement.of("SELECT SingerId, AlbumId, AlbumTitle FROM Albums"),
+        Options.tag("app=concert,env=dev,action=select"))) {
+      while (resultSet.next()) {
+        System.out.printf(
+            "%d %d %s\n", resultSet.getString(0), resultSet.getLong(1), resultSet.getLong(2));
+      }
+    }
+  }
+  // [END spanner_set_request_tag]
+}