Added Cloud SQL MySQL Servlet connectivity sample. (#1231)

* Added MySQL Servlet connectivity sample.

Fix checkstyle violations.

* Partially address lesv feedback.

* Address rest of lesv's feedback.

* Address additional feedback.

cloud-sql/mysql/servlet/README.md

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+# Connecting to Cloud SQL - MySQL
+
+## Before you begin
+
+1. If you haven't already, set up a Java Development Environment (including google-cloud-sdk and 
+maven utilities) by following the [java setup guide](https://cloud.google.com/java/docs/setup) and 
+[create a project](https://cloud.google.com/resource-manager/docs/creating-managing-projects#creating_a_project).
+
+1. Create a 2nd Gen Cloud SQL Instance by following these 
+[instructions](https://cloud.google.com/sql/docs/mysql/create-instance). Note the connection string,
+database user, and database password that you create.
+
+1. Create a database for your application by following these 
+[instructions](https://cloud.google.com/sql/docs/mysql/create-manage-databases). Note the database
+name. 
+
+1. Create a service account with the 'Cloud SQL Client' permissions by following these 
+[instructions](https://cloud.google.com/sql/docs/mysql/connect-external-app#4_if_required_by_your_authentication_method_create_a_service_account).
+Download a JSON key to use to authenticate your connection. 
+
+1. Use the information noted in the previous steps:
+```bash
+export GOOGLE_APPLICATION_CREDENTIALS=/path/to/service/account/key.json
+export CLOUD_SQL_CONNECTION_NAME='<MY-PROJECT>:<INSTANCE-REGION>:<MY-DATABASE>'
+export DB_USER='my-db-user'
+export DB_PASS='my-db-pass'
+export DB_NAME='my_db'
+```
+Note: Saving credentials in environment variables is convenient, but not secure - consider a more
+secure solution such as [Cloud KMS](https://cloud.google.com/kms/) to help keep secrets safe.
+
+## Deploying locally
+
+To run this application locally, run the following command inside the project folder:
+
+```bash
+mvn jetty:run
+```
+
+Navigate towards `http://127.0.0.1:8080` to verify your application is running correctly.
+
+## Google App Engine Standard
+
+To run on GAE-Standard, create an AppEngine project by following the setup for these 
+[instructions](https://cloud.google.com/appengine/docs/standard/java/quickstart#before-you-begin) 
+and verify that 
+[appengine-maven-plugin](https://cloud.google.com/java/docs/setup#optional_install_maven_or_gradle_plugin_for_app_engine)
+ has been added in your build section as a plugin.
+
+
+### Development Server
+
+The following command will run the application locally in the the GAE-development server:
+```bash
+mvn appengine:run
+```
+
+### Deploy to Google Cloud
+
+First, update `src/main/webapp/WEB-INF/appengine-web.xml` with the correct values to pass the 
+environment variables into the runtime.
+
+Next, the following command will deploy the application to your Google Cloud project:
+```bash
+mvn appengine:deploy
+```

cloud-sql/mysql/servlet/pom.xml

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+<!--
+  Copyright 2018 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.
+-->
+<project>
+  <modelVersion>4.0.0</modelVersion>
+  <packaging>war</packaging>
+  <version>1.0-SNAPSHOT</version>
+  <groupId>com.example.cloudsql</groupId>
+  <artifactId>tabs-vs-spaces</artifactId>
+
+  <!--
+    The parent pom defines common style checks and testing strategies for our samples.
+    Removing or replacing it should not affect the execution of the samples in anyway.
+  -->
+  <parent>
+    <groupId>com.google.cloud.samples</groupId>
+    <artifactId>shared-configuration</artifactId>
+    <version>1.0.10</version>
+  </parent>
+
+  <properties>
+    <maven.compiler.target>1.8</maven.compiler.target>
+    <maven.compiler.source>1.8</maven.compiler.source>
+    <failOnMissingWebXml>false</failOnMissingWebXml>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>javax.servlet</groupId>
+      <artifactId>javax.servlet-api</artifactId>
+      <version>3.1.0</version>
+      <type>jar</type>
+      <scope>provided</scope>
+    </dependency>
+    <dependency>
+      <groupId>javax.servlet</groupId>
+      <artifactId>jstl</artifactId>
+      <version>1.2</version>
+    </dependency>
+    <dependency>
+      <groupId>mysql</groupId>
+      <artifactId>mysql-connector-java</artifactId>
+      <version>8.0.11</version>
+    </dependency>
+    <dependency>
+      <groupId>com.google.cloud.sql</groupId>
+      <artifactId>mysql-socket-factory-connector-j-8</artifactId>
+      <version>1.0.11</version>
+    </dependency>
+    <dependency>
+      <groupId>com.zaxxer</groupId>
+      <artifactId>HikariCP</artifactId>
+      <version>3.1.0</version>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.eclipse.jetty</groupId>
+        <artifactId>jetty-maven-plugin</artifactId>
+        <version>9.4.10.v20180503</version>
+        <configuration>
+          <scanIntervalSeconds>1</scanIntervalSeconds>
+        </configuration>
+      </plugin>
+      <!-- Only required for AppEngine Deployments -->
+      <plugin>
+        <groupId>com.google.cloud.tools</groupId>
+        <artifactId>appengine-maven-plugin</artifactId>
+        <version>1.3.2</version>
+     </plugin>
+    </plugins>
+  </build>
+</project>

cloud-sql/mysql/servlet/src/main/java/com/example/cloudsql/ConnectionPoolContextListener.java

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+/*
+ * Copyright 2018 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.cloudsql;
+
+import com.zaxxer.hikari.HikariConfig;
+import com.zaxxer.hikari.HikariDataSource;
+import java.sql.Connection;
+import java.sql.PreparedStatement;
+import java.sql.SQLException;
+import java.util.logging.Logger;
+import javax.servlet.ServletContextEvent;
+import javax.servlet.ServletContextListener;
+import javax.servlet.annotation.WebListener;
+import javax.sql.DataSource;
+
+@WebListener("Creates a connection pool that is stored in the Servlet's context for later use.")
+public class ConnectionPoolContextListener implements ServletContextListener {
+
+  private static final Logger LOGGER = Logger.getLogger(IndexServlet.class.getName());
+
+  // Saving credentials in environment variables is convenient, but not secure - consider a more
+  // secure solution such as https://cloud.google.com/kms/ to help keep secrets safe.
+  private static final String CLOUD_SQL_INSTANCE_NAME = System.getenv("CLOUD_SQL_INSTANCE_NAME");
+  private static final String DB_USER = System.getenv("DB_USER");
+  private static final String DB_PASS = System.getenv("DB_PASS");
+  private static final String DB_NAME = System.getenv("DB_NAME");
+
+  private DataSource createConnectionPool() {
+    // [START cloud_sql_mysql_connection_pool]
+    // The configuration object specifies behaviors for the connection pool.
+    HikariConfig config = new HikariConfig();
+
+    // Configure which instance and what database user to connect with.
+    config.setJdbcUrl(String.format("jdbc:mysql:///%s", DB_NAME));
+    config.setUsername(DB_USER); // e.g. "root", "postgres"
+    config.setPassword(DB_PASS); // e.g. "my-password"
+
+    // For Java users, the Cloud SQL JDBC Socket Factory can provide authenticated connections.
+    // See https://github.com/GoogleCloudPlatform/cloud-sql-jdbc-socket-factory for details.
+    config.addDataSourceProperty("socketFactory", "com.google.cloud.sql.mysql.SocketFactory");
+    config.addDataSourceProperty("cloudSqlInstance", CLOUD_SQL_INSTANCE_NAME);
+    config.addDataSourceProperty("useSSL", "false");
+
+    // ... Specify additional connection properties here.
+
+    // [START_EXCLUDE]
+
+    // [START cloud_sql_limit_connections]
+    // maximumPoolSize limits the total number of concurrent connections this pool will keep. Ideal
+    // values for this setting are highly variable on app design, infrastructure, and database.
+    config.setMaximumPoolSize(5);
+    // minimumIdle is the minimum number of idle connections Hikari maintains in the pool.
+    // Additional connections will be established to meet this value unless the pool is full.
+    config.setMinimumIdle(5);
+    // [END cloud_sql_limit_connections]
+
+    // [START cloud_sql_connection_timeout]
+    // setConnectionTimeout is the maximum number of milliseconds to wait for a connection checkout.
+    // Any attempt to retrieve a connection from this pool that exceeds the set limit will throw an
+    // SQLException.
+    config.setConnectionTimeout(10000); // 10 seconds
+    // idleTimeout is the maximum amount of time a connection can sit in the pool. Connections that
+    // sit idle for this many milliseconds are retried if minimumIdle is exceeded.
+    config.setIdleTimeout(600000); // 10 minutes
+    // [END cloud_sql_connection_timeout]
+
+    // [START cloud_sql_connection_backoff]
+    // Hikari automatically delays between failed connection attempts, eventually reaching a
+    // maximum delay of `connectionTimeout / 2` between attempts.
+    // [END cloud_sql_connection_backoff]
+
+    // [START cloud_sql_connection_lifetime]
+    // maxLifetime is the maximum possible lifetime of a connection in the pool. Connections that
+    // live longer than this many milliseconds will be closed and reestablished between uses. This
+    // value should be several minutes shorter than the database's timeout value to avoid unexpected
+    // terminations.
+    config.setMaxLifetime(1800000); // 30 minutes
+    // [END cloud_sql_connection_lifetime]
+
+    // [END_EXCLUDE]
+
+    // Initialize the connection pool using the configuration object.
+    DataSource pool = new HikariDataSource(config);
+    // [END cloud_sql_mysql_connection_pool]
+    return pool;
+  }
+
+  private void createTable(DataSource pool) throws SQLException {
+    // Safely attempt to create the table schema.
+    try (Connection conn = pool.getConnection()) {
+      PreparedStatement createTableStatement = conn.prepareStatement(
+          "CREATE TABLE IF NOT EXISTS votes ( "
+              + "vote_id SERIAL NOT NULL, time_cast timestamp NOT NULL, candidate CHAR(6) NOT NULL,"
+              + " PRIMARY KEY (vote_id) );"
+      );
+      createTableStatement.execute();
+    }
+  }
+
+  @Override
+  public void contextDestroyed(ServletContextEvent event) {
+    // This function is called when the Servlet is destroyed.
+    HikariDataSource pool = (HikariDataSource) event.getServletContext().getAttribute("my-pool");
+    if (pool != null) {
+      pool.close();
+    }
+  }
+
+  @Override
+  public void contextInitialized(ServletContextEvent event) {
+    // This function is called when the application starts and will safely create a connection pool
+    // that can be used to connect to.
+    DataSource pool = (DataSource) event.getServletContext().getAttribute("my-pool");
+    if (pool == null) {
+      pool = createConnectionPool();
+      event.getServletContext().setAttribute("my-pool", pool);
+    }
+    try {
+      createTable(pool);
+    } catch (SQLException ex) {
+      throw new RuntimeException("Unable to verify table schema. Please double check the steps"
+          + "in the README and try again.", ex);
+    }
+  }
+}