Cloud SQL connect from Appengine

I want to coonnect to cloud sql mysql instance in gcp from my java appengine project.
I am not able to under stand what this is INSTANCE_UNIX_SOCKET in the configuration section.
I want to connect to this instance from my java appengine project. I have mysqlsocketfactoryconnector jar in my build path

import com.zaxxer.hikari.HikariConfig;
import com.zaxxer.hikari.HikariDataSource;
import javax.sql.DataSource;

public class ConnectorConnectionPoolFactory extends ConnectionPoolFactory {

  // Note: Saving credentials in environment variables is convenient, but not
  // secure - consider a more secure solution such as
  // Cloud Secret Manager (https://cloud.google.com/secret-manager) to help
  // keep secrets safe.
  private static final String INSTANCE_CONNECTION_NAME =
      System.getenv("INSTANCE_CONNECTION_NAME");
  private static final String INSTANCE_UNIX_SOCKET = System.getenv("INSTANCE_UNIX_SOCKET");
  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");

  public static DataSource createConnectionPool() {
    // The configuration object specifies behaviors for the connection pool.
    HikariConfig config = new HikariConfig();

    // The following URL is equivalent to setting the config options below:
    // jdbc:mysql:///<DB_NAME>?cloudSqlInstance=<INSTANCE_CONNECTION_NAME>&
    // socketFactory=com.google.cloud.sql.mysql.SocketFactory&user=<DB_USER>&password=<DB_PASS>
    // See the link below for more info on building a JDBC URL for the Cloud SQL JDBC Socket Factory
    // https://github.com/GoogleCloudPlatform/cloud-sql-jdbc-socket-factory#creating-the-jdbc-url

    // 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", "mysql"
    config.setPassword(DB_PASS); // e.g. "my-password"

    config.addDataSourceProperty("socketFactory", "com.google.cloud.sql.mysql.SocketFactory");
    config.addDataSourceProperty("cloudSqlInstance", INSTANCE_CONNECTION_NAME);

    // Unix sockets are not natively supported in Java, so it is necessary to use the Cloud SQL
    // Java Connector to connect. When setting INSTANCE_UNIX_SOCKET, the connector will 
    // call an external package that will enable Unix socket connections.
    // Note: For Java users, the Cloud SQL Java Connector can provide authenticated connections
    // which is usually preferable to using the Cloud SQL Proxy with Unix sockets.
    // See https://github.com/GoogleCloudPlatform/cloud-sql-jdbc-socket-factory for details.
    if (INSTANCE_UNIX_SOCKET != null) {
      config.addDataSourceProperty("unixSocketPath", INSTANCE_UNIX_SOCKET);
    }


    // ... Specify additional connection properties here.
    // ...

    // Initialize the connection pool using the configuration object.
    return new HikariDataSource(config);
  }
}

You can ignore INSTANCE_UNIX_SOCKET here -- we've added it to the sample code for people who might want to connect to the Unix socket. In almost all cases, you'll want to use the socket factory directly and bypass the Unix socket. So just do this:

import com.zaxxer.hikari.HikariConfig;
import com.zaxxer.hikari.HikariDataSource;
import javax.sql.DataSource;

public class ConnectorConnectionPoolFactory extends ConnectionPoolFactory {
  private static final String INSTANCE_CONNECTION_NAME =
      System.getenv("INSTANCE_CONNECTION_NAME");
  private static final String INSTANCE_UNIX_SOCKET = System.getenv("INSTANCE_UNIX_SOCKET");
  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");

  public static DataSource createConnectionPool() {
    HikariConfig config = new HikariConfig();
    config.setJdbcUrl(String.format("jdbc:mysql:///%s", DB_NAME));
    config.setUsername(DB_USER); // e.g. "root", "mysql"
    config.setPassword(DB_PASS); // e.g. "my-password"

    config.addDataSourceProperty("socketFactory", "com.google.cloud.sql.mysql.SocketFactory");
    config.addDataSourceProperty("cloudSqlInstance", INSTANCE_CONNECTION_NAME);
    return new HikariDataSource(config);
  }
}