R2DBC Code Example (Native API)

Complete Java code example using the MariaDB Connector/R2DBC native API to query a MariaDB table with MariadbConnectionFactory and reactive Flux result handling.

Overview

The following example uses the native R2DBC API to select data from the table defined in Setup for Examples. Complete information on using Connector/R2DBC natively is available.

//Module Imports
import org.mariadb.r2dbc.MariadbConnectionConfiguration;
import org.mariadb.r2dbc.MariadbConnectionFactory;
import io.r2dbc.spi.Connection;
import io.r2dbc.spi.Statement;
import io.r2dbc.spi.Result;
import io.r2dbc.spi.Row;
import io.r2dbc.spi.RowMetadata;
import reactor.core.publisher.Flux;

public class App {

   // Connection Configuration
   private static MariadbConnectionConfiguration conf;
   private static MariadbConnectionFactory connFactory;
   private static Connection conn;

   public static void main(String[] argv) {

      // Initialize Connection
      initConnection();

      // Print contacts
      printContactList();

      // Close Connection
      conn.close();
   }

   public static void initConnection() {

      try {
         // Configure the Connection
         conf = MariadbConnectionConfiguration.builder()
              .host("192.0.2.1").port(3306)
              .username("db_user").password("db_user_password")
              .database("test").build();

         // Instantiate a Connection Factory
         connFactory = new MariadbConnectionFactory(conf);

         // Instantiate a Connection
         conn = connFactory.create().block();
      }
      catch (java.lang.IllegalArgumentException e) {
         System.err.println("Issue encountered while getting connection");
         e.printStackTrace();
      }
   }

   public static void printContactList() {

      try {
         // Initialize Statement
         Statement stmnt = conn.createStatement(
            "SELECT first_name, last_name, email FROM test.contacts");

         // Execute Statement and Iterate over the Result-set
         for (String contact_entry : Flux.from(stmnt.execute()).flatMap( res ->
            res.map( (row, metadata) -> {

            return String.format( "- %s %s <%s>",
               // Get First Name
               row.get(0, String.class),

               //  Get Last Name
               row.get(1, String.class),

               //Get Email
               row.get(2, String.class));
         })).toIterable()) {

            System.out.println(contact_entry);
         }
      }
      // Catch Exception
      catch (java.lang.IllegalArgumentException e) {
         System.err.println("Encountered issue querying contact list");
         e.printStackTrace();
      }
   }
}

Example output:

* John Smith <[e-mail]>
* Jon Smith <[e-mail]>

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