<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD//EN"
    "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

    <session-factory>
       
        <property name="show_sql">true</property>
       
        <property name="dialect">org.hibernate.dialect.HSQLDialect</property>
        <property name="connection.driver_class">org.hsqldb.jdbcDriver</property>
        <property name="connection.url">jdbc:hsqldb:/C:\Documents and Settings\brian\Desktop\Simple Hibernate Demo/data/hsqldb</property>
        <property name="connection.username">sa</property>
        <property name="connection.password"></property>
       
        <property name="c3p0.min_size">5</property>
        <property name="c3p0.max_size">20</property>       
        <property name="c3p0.timeout">300</property>
        <property name="c3p0.max_statements">50</property>
        <property name="c3p0.idle_test_period">3000</property>

        <mapping resource="Account.hbm.xml"/>
        <mapping resource="Role.hbm.xml"/>

    </session-factory>

</hibernate-configuration>

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">         

<hibernate-mapping
    package="com.briankuhn.demo.hibernate.simple">

    <class name="Account">
        <id name="id">
            <generator class="hilo"/>
        </id>
        <property name="username" not-null="true"/>
        <property name="password" not-null="true"/>
        <set name="roles" table="accountroles">
            <key column="account_id"/>
            <many-to-many column="role_id" class="Role"/>
        </set>
    </class>

</hibernate-mapping>

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
      "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
      "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping
    package="com.briankuhn.demo.hibernate.simple">

    <class name="Role">
        <id name="id">
            <generator class="hilo"/>
        </id>
        <property name="name" not-null="true"/>
        <set name="accounts" table="accountroles" inverse="true">
            <key column="role_id"/>
            <many-to-many column="account_id" class="Account"/>
        </set>
    </class>

</hibernate-mapping>

       Session session = sessionFactory.openSession();
        Transaction transaction = null;   
        try {
            transaction = session.beginTransaction();   
           
            Account account = new Account();
            account.setUsername("briankuhn");
            account.setPassword("hibernate");
            session.persist(account);
            transaction.commit();   //Works fine...
           
            Role userRole = new Role();
            userRole.setName("user");
            session.persist(userRole);
            transaction.commit();   //Works fine...
           
            Role adminRole = new Role();
            adminRole.setName("admin");
            session.persist(adminRole);
            transaction.commit();  //Works fine...
           
            Set accounts = new HashSet();
            accounts.add(account);
            userRole.setAccounts(accounts);
            adminRole.setAccounts(accounts);
           
            Set roles = new HashSet();
            roles.add(userRole);
            roles.add(adminRole);           
            account.setRoles(roles);
           
            transaction.commit();  //StackOverflowError here
        }
        catch (Throwable t) {
            t.printStackTrace();
            if (transaction != null) {
                transaction.rollback();
            }   
        }
        finally {
            session.close();
        }

alter table accountroles drop constraint FK421758B09D5D27B4;
alter table accountroles drop constraint FK421758B0672A82A0;
drop table Account if exists;
drop table Role if exists;
drop table accountroles if exists;
drop table hibernate_unique_key if exists;
create table Account (
   id bigint not null,
   username varchar(255) not null,
   password varchar(255) not null,
   primary key (id)
);
create table Role (
   id bigint not null,
   name varchar(255) not null,
   primary key (id)
);
create table accountroles (
   account_id bigint not null,
   role_id bigint not null,
   primary key (account_id, role_id)
);
alter table accountroles add constraint FK421758B09D5D27B4 foreign key (role_id) references Role;
alter table accountroles add constraint FK421758B0672A82A0 foreign key (account_id) references Account;
create table hibernate_unique_key (
    next_hi integer
);
insert into hibernate_unique_key values ( 0 );

Set userAccounts = new HashSet();
userAccounts.add(account);
userRole.setAccounts(userAccounts);

Set adminAccounts = new HashSet();
adminAccounts.add(account);
adminRole.setAccounts(adminAccounts);