WARN SqlExceptionHelper:143 - SQL Error: 0, SQLState: 08S01- SqlExceptionHelper:144 - Communications link failure

Question

I have problem with Hibernate (hibernate-core-4.1.9.Final.jar)

Case 1: Hibernate testing inside for loop. Everything went well.

for(in         


        

Answer 1

The problem was happening because of the small value for time_out variable on the MySQL server.

In my situation, time_out was set to 1 minute. Using C3PO pooling mechanism we can optimize JDBC.

Download c3p0 -> http://sourceforge.net/projects/c3p0/

I'm using hibernate 3.0.

hibernate.cfg.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
          "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
          "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
 
<hibernate-configuration>
 
    <session-factory>
       
         <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
          <property name="connection.url">jdbc:mysql://databasehost:3306/databasename</property>
          <property name="connection.username">user</property>
          <property name="connection.password">psw</property>
          <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
          <property name="hibernate.hbm2ddl.auto">update</property>
         
          <property name="show_sql">false</property>
         
       <!-- Hibernate c3p0 settings-->
        <property name="connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</property>
        <property name="hibernate.c3p0.acquire_increment">3</property>
        <property name="hibernate.c3p0.idle_test_period">10</property>
        <property name="hibernate.c3p0.min_size">5</property>
        <property name="hibernate.c3p0.max_size">75</property>
        <property name="hibernate.c3p0.max_statements">10</property>
        <property name="hibernate.c3p0.timeout">50</property>
        <property name="hibernate.c3p0.preferredTestQuery">select 1</property>
        <property name="hibernate.c3p0.testConnectionOnCheckout">true</property>
          
         <!-- Mapping files -->
        <mapping class="xxx.xxx.xxx.xxx" />
        <mapping class="xxx.xxx.xxx.xxx" />
        <mapping class="xxx.xxx.xxx.xxx" />
        <mapping class="xxx.xxx.xxx.xxx" />
        
       
    </session-factory>
</hibernate-configuration> 

PersistenceManager.java

import java.io.PrintStream;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.cfg.Configuration;

public class PersistenceManager
{
  private static SessionFactory sessionFactory = null;

  private static PersistenceManager singleton = null;

  public static PersistenceManager getInstance()
  {
    if (singleton == null)
    {
      singleton = new PersistenceManager();
    }

    return singleton;
  }

  public SessionFactory getSessionFactory()
  {
    if (sessionFactory == null)
      createSessionFactory();
    return sessionFactory;
  }

  protected void createSessionFactory()
  {    
    sessionFactory = new AnnotationConfiguration().configure()
      .buildSessionFactory();
  }

  public void destroySessionFactory()
  {
    if (sessionFactory != null)
    {
      sessionFactory.close();
      sessionFactory = null;
    }
  }
}

Example 1:

import org.hibernate.HibernateException;
import org.hibernate.Query;
import org.hibernate.Session;

public Users Login( String username,  String password)
  {
    Session session = null;
    try
    {
      String hql = "select u from Users u where u.username like :p1 and u.password like :p2";
      session = PersistenceManager.getInstance().getSessionFactory().openSession();

      Query q = session.createQuery(hql)
        .setParameter("p1", username)
        .setParameter("p2", password);

      if (q.list().size() == 0)
      {
        session.close();
        return new Users();
      }

      Users user = (Users)q.list().get(0);
      session.close();
      return user;
    }
    catch (Exception e)
    {
      session.close();
     
    }
  }

Example 2:

import org.hibernate.HibernateException;
import org.hibernate.Query;
import org.hibernate.Session;
 public String Registration(Users u) { 

    Session session = null;
    try
    {
      String hql = "select u from Users u where u.username like :p1";

      session = PersistenceManager.getInstance().getSessionFactory().openSession();

      Query q = session.createQuery(hql).setParameter("p1", u.getUsername());

      if (q.list().size() == 0)
      {
        session.beginTransaction();
        session.persist(u);
        session.getTransaction().commit();
        session.close();
        return new Boolean(true).toString();
      }

      session.close();

      return new Boolean(false).toString();
    }
    catch (Exception e)
    {
      return e.toString();
    }
  }

Answer 2

I had the same issue just because I forgot to wrap my hibernate code in a transaction. Apparently the connection to DB is not closed until you commit a transaction. Here is a valid example:

Session session = HibernateUtils.getSession();
Transaction tx = session.beginTransaction();
Category cat = null;

try{
    cat = (Category)session.get(Category.class, 1);
    tx.commit();
}catch(Exception ex){
    tx.rollback();
}finally{           
    session.close();
}

return cat;