Too many connections in Hibernate

Question

I'm trying to learn Hibernate and I wrote the simplest Person Entity and I was trying to insert 2000 of them. I know I'm using deprecated methods, I will try to figure out what are the new ones later.

First, here is the class Person:

@Entity
public class Person {

        private int id;
        private String name;

        @Id
        @GeneratedValue(strategy = GenerationType.TABLE, generator = "person")
        @TableGenerator(name = "person", table = "sequences", allocationSize = 1)
        public int getId() {
                return id;
        }

        public void setId(int id) {
                this.id = id;
        }

        public String getName() {
                return name;
        }

        public void setName(String name) {
                this.name = name;
        }

}

Then I wrote a small App class that insert 2000 entities with a loop:

public class App {

        private static AnnotationConfiguration config;

        public static void insertPerson() {
                SessionFactory factory = config.buildSessionFactory();
                Session session = factory.getCurrentSession();
                session.beginTransaction();
                Person aPerson = new Person();
                aPerson.setName("John");
                session.save(aPerson);
                session.getTransaction().commit();
        }

        public static void main(String[] args) {
                config = new AnnotationConfiguration();
                config.addAnnotatedClass(Person.class);
                config.configure("hibernate.cfg.xml"); //is the default already
                new SchemaExport(config).create(true, true); //print and execute
                for (int i = 0; i < 2000; i++) {
                        insertPerson();
                }
        }

}

What I get after a while is:

Exception in thread "main" org.hibernate.exception.JDBCConnectionException: Cannot open connection

Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Too many connections

Now I know that probably if I put the transaction outside the loop it would work, but mine was a test to see what happens when executing multiple transactions. And since there is only one open at each time, it should work.

I tried to add session.close() after the commit, but I got

Exception in thread "main" org.hibernate.SessionException: Session was already closed

So how to solve the problem?

Answer 1

The problem is not about Session s and transactions, it's about SessionFactory . You create a new SessionFactory on each iteration and don't close it.

Usually you need only one instance of SessionFactory per application, so that you should create it outside of the loop, and close it explicitly when your application stops.

Obtaining Session s and work with transactions inside the loop is correct.