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3.3. JDBC connections

It is advisable to have the org.hibernate.SessionFactory create and pool JDBC connections for you. If you take this approach, opening a org.hibernate.Session is as simple as: 
Session session = sessions.openSession(); // open a new Session
Once you start a task that requires access to the database, a JDBC connection will be obtained from the pool.
Before you can do this, you first need to pass some JDBC connection properties to Hibernate. All Hibernate property names and semantics are defined on the class org.hibernate.cfg.Environment. The most important settings for JDBC connection configuration are outlined below.
Hibernate will obtain and pool connections using java.sql.DriverManager if you set the following properties:

Table 3.1. Hibernate JDBC Properties

Property name Purpose
hibernate.connection.driver_class JDBC driver class
hibernate.connection.url JDBC URL
hibernate.connection.username database user
hibernate.connection.password database user password
hibernate.connection.pool_size maximum number of pooled connections
Hibernate's own connection pooling algorithm is, however, quite rudimentary. It is intended to help you get started and is not intended for use in a production system, or even for performance testing. You should use a third party pool for best performance and stability. Just replace the hibernate.connection.pool_size property with connection pool specific settings. This will turn off Hibernate's internal pool. For example, you might like to use c3p0.
C3P0 is an open source JDBC connection pool distributed along with Hibernate in the lib directory. Hibernate will use its org.hibernate.connection.C3P0ConnectionProvider for connection pooling if you set hibernate.c3p0.* properties. If you would like to use Proxool, refer to the packaged hibernate.properties and the Hibernate web site for more information.
The following is an example hibernate.properties file for c3p0: 
hibernate.connection.driver_class = org.postgresql.Driver
hibernate.connection.url = jdbc:postgresql://localhost/mydatabase
hibernate.connection.username = myuser
hibernate.connection.password = secret
hibernate.c3p0.min_size=5
hibernate.c3p0.max_size=20
hibernate.c3p0.timeout=1800
hibernate.c3p0.max_statements=50
hibernate.dialect = org.hibernate.dialect.PostgreSQLDialect
For use inside an application server, you should almost always configure Hibernate to obtain connections from an application server javax.sql.Datasource registered in JNDI. You will need to set at least one of the following properties:

Table 3.2. Hibernate Datasource Properties

Property name Purpose
hibernate.connection.datasource datasource JNDI name
hibernate.jndi.url URL of the JNDI provider (optional)
hibernate.jndi.class class of the JNDI InitialContextFactory (optional)
hibernate.connection.username database user (optional)
hibernate.connection.password database user password (optional)
Here is an example hibernate.properties file for an application server provided JNDI datasource: 
hibernate.connection.datasource = java:/comp/env/jdbc/test
hibernate.transaction.factory_class = \
    org.hibernate.transaction.JTATransactionFactory
hibernate.transaction.manager_lookup_class = \
    org.hibernate.transaction.JBossTransactionManagerLookup
hibernate.dialect = org.hibernate.dialect.PostgreSQLDialect
JDBC connections obtained from a JNDI datasource will automatically participate in the container-managed transactions of the application server.
Arbitrary connection properties can be given by prepending "hibernate.connection" to the connection property name. For example, you can specify a charSet connection property using hibernate.connection.charSet.
You can define your own plugin strategy for obtaining JDBC connections by implementing the interface org.hibernate.connection.ConnectionProvider, and specifying your custom implementation via the hibernate.connection.provider_class property.