IsolationLevel.java

/*
 * 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.spanner.jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Properties;

final class IsolationLevel {

  static void isolationLevel(
      final String project,
      final String instance,
      final String database,
      final Properties properties)
      throws SQLException {
    String url = String.format(
        "jdbc:cloudspanner:/projects/%s/instances/%s/databases/%s",
        project, instance, database);
    try (Connection connection = DriverManager.getConnection(url, properties)) {
      connection.setAutoCommit(false);

      // Spanner supports setting the isolation level to:
      // 1. TRANSACTION_SERIALIZABLE (this is the default)
      // 2. TRANSACTION_REPEATABLE_READ

      // The following line sets the default isolation level that will be used
      // for all read/write transactions on this connection.
      connection.setTransactionIsolation(
          Connection.TRANSACTION_REPEATABLE_READ);

      // This query will not take any locks when using
      // isolation level repeatable read.
      try (ResultSet resultSet = connection
          .createStatement()
          .executeQuery("SELECT SingerId, Active "
              + "FROM Singers "
              + "ORDER BY LastName")) {
        while (resultSet.next()) {
          try (PreparedStatement statement = connection.prepareStatement(
              "INSERT OR UPDATE INTO SingerHistory "
                  + "(SingerId, Active, CreatedAt) "
                  + "VALUES (?, ?, CURRENT_TIMESTAMP)")) {
            statement.setLong(1, resultSet.getLong(1));
            statement.setBoolean(2, resultSet.getBoolean(2));
            statement.executeUpdate();
          }
        }
      }
      connection.commit();
    }
  }

  private IsolationLevel() {
  }
}