Why does this simple JDBC/JOOQ code creates 10 connections to my database?

Question

Im working on a spring project ran on a local environment using SpringToolSuite. I'm using Putty to create a tunel to access an app server from which i can query my MySQL database (i have to use SSH). So i'm running this simple code:

public static void getConnection() {
        try {
            connection = DriverManager.getConnection(url, user, password);
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        DSLContext create = DSL.using(connection, SQLDialect.MYSQL);

        Personne personne = Personne.PERSONNE.as("personne");
        Evenement evenement = Evenement.EVENEMENT.as("evenement");
        Genealogie genealogie = Genealogie.GENEALOGIE.as("genealogie");
        Lieu lieu = Lieu.LIEU.as("lieu");
        
        Result<Record3<Integer,Integer,String>> result = create
                .select(DSL.countDistinct(personne.ID).as("countRs"), 
                        evenement.IDGROUPE2.as("group2Rs"),
                        lieu.LIBELLE.as("libelleRs"))
                .from(evenement.innerJoin(personne)
                            .on(personne.ID.eq(evenement.IDPERS))
                        .innerJoin(genealogie)
                            .on(genealogie.ID.eq(personne.IDGEN))
                        .innerJoin(lieu)
                            .on(lieu.ID.eq(evenement.IDGROUPE2)))
                .where(personne._NOM.eq(" ")
                        .and((personne._PRENOM.eq(" ")
                            .or(personne._PRENOM.like(" -%"))))
                        .and(evenement.IDPERS.isNotNull())
                        .and(lieu.LIBELLE.isNotNull())
                        .and(genealogie.STATUS.ge(Byte.valueOf("1")))
                        .and(personne.CONTEMPORAIN.eq(Byte.valueOf("0"))))
                .groupBy(evenement.IDGROUPE2)
                .fetch();

        System.out.println("countRs group2Rs libellesRs");
        System.out.println("---------------------------");
        for (Record r : result) {
            System.out.println(r.get("countRs")+" "+r.get("group2Rs")+" "+r.get("libelleRs"));
        }
        
        try {
            create.close();
            connection.close();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    } 

As you can see it's basicly just opening the connection with the database, making a query and closing the connection/query, nothing special.

But when i check the client connections to my database using MySQL Workbench i can see that my code opened 10 connection:

And as you can see, only a single one of these connections is actualy executing the query. Is there something i don't know about how JOOQ executes queries? Or mabe it is because i'm using Putty to access my remote server and it somehow creates many connections?

Answer 1

Since you're using HikariCP in your project, you should not create new connections manually using DriverManager :

// Don't do this
connection = DriverManager.getConnection(url, user, password);
DSLContext create = DSL.using(connection, SQLDialect.MYSQL);

Instead, use HikariCP as a DataSource and pass that to jOOQ:

// Do this
DSLContext create = DSL.using(dataSource, SQLDialect.MYSQL);

Now, you don't have to do any resource management anymore, because jOOQ / Hikari do this for you, behind the scenes (ie no close() calls)