Java Platform, Enterprise Edition (Java EE) 8
The Java EE Tutorial
To store, organize, and retrieve data, most applications use a
relational database. Java EE components may access relational
databases through the JDBC API. For information on this API, see
In the JDBC API, databases are accessed by using
DataSource objects. A
DataSource has a set of properties that identify and describe the
real-world data source that it represents. These properties include such
information as the location of the database server, the name of the
database, the network protocol to use to communicate with the server,
and so on. In GlassFish Server, a data source is called a JDBC resource.
Applications access a data source by using a connection, and a
DataSource object can be thought of as a factory for connections to
the particular data source that the
DataSource instance represents. In
DataSource implementation, a call to the
method returns a connection object that is a physical connection to the
DataSource object may be registered with a JNDI naming service. If
so, an application can use the JNDI API to access that
object, which can then be used to connect to the data source it
DataSource objects that implement connection pooling also produce a
connection to the particular data source that the
represents. The connection object that the
returns is a handle to a
PooledConnection object rather than a
physical connection. An application uses the connection object in the
same way that it uses a connection. Connection pooling has no effect on
application code except that a pooled connection, like all connections,
should always be explicitly closed. When an application closes a
connection that is pooled, the connection is returned to a pool of
reusable connections. The next time
getConnection is called, a handle
to one of these pooled connections will be returned if one is available.
Because connection pooling avoids creating a new physical connection
every time one is requested, applications can run significantly faster.
A JDBC connection pool is a group of reusable connections for a particular database. Because creating each new physical connection is time consuming, the server maintains a pool of available connections to increase performance. When it requests a connection, an application obtains one from the pool. When an application closes a connection, the connection is returned to the pool.
Applications that use the Persistence API specify the
object they are using in the
jta-data-source element of the
This is typically the only reference to a JDBC object for a persistence unit. The application code does not refer to any JDBC objects.