Data Sources

In web applications database queries are usually made under program control.

Controlling programs include the Java beans making up the model part of the MVC architecture.

Java programs can make database queries using the Java DataBase Connectivity (JDBC) interface.

JDBC makes database connections from within a program.
For efficiency, database connections must be managed through database connection pools.
JDBC accesses connection pools through data sources

Before JDBC can be used in a Java program, connection pools and data sources must be set up in advance within the application server, in our case, Glassfish.

If you have NetBeans open and have already (successfully) run a web app, then the Glassfish server is running.

If not, you can manually start Glassfish from within the NetBeans Services tab by opening the Servers node, right clicking Glassfish Server 3.1.1, and choosing Start:

Once the Glassfish server is running, you can get to the web-based Glassfish administration console by pointing your browser to localhost:4848.

You can also get there from the NetBeans interface:

Problem:

Opening a connection to a database can be time consuming; you cannot open a new connection for every page request.

On the other hand, you cannot open a connection for each user and keep it open; databases put a limit on open connections.

Solution:

Create a pool of always-open connections and reuse them when necessary:

"Opening a connection" in a Java program means getting a connection from the pool
"Closing a connection" in a Java program means returning the connection to the pool

This section describes how to use Glassfish to configure a connection pool.

It assumes that the database has already been created — see Using Derby in NetBeans.

In the task tree under Resources open the JDBC node and click JDBC Connection Pools.

You should see some built-in pools listed.

Click New... to create a new pool:

We will create a connection pool for the Cars database called CarPool.

Make sure the resource type is javax.sql.Datasource and the vendor is Derby. Click Next.

The general settings, pool settings, and transaction settings can be left with their default values.

The built-in security mechanism, however, causes problems so we need to delete it.

Scroll down to the Additional Properties table, check Security Mechanism and click Delete Properties:

Three property values need to be set:

DatabaseName (example: Cars)
User (example: app)
Password (example: password)

Then click Finish.

Now test the new pool's connection to the database.

Click on CarPool to bring you back to the configuration window and click Ping.

If you don't see Ping Succeeded then most likely the database has not been started (connected to) in NetBeans, or the authentication information is incorrect.

Database driver vendors (Derby, MySQL, Oracle, etc.) can offer connection pooling by implementing the javax.sql.DataSource interface, which is part of the JDBC interface.

A database resource, or data source, hides the details of connection pooling from the programs that need to access the database.

To use data sources,

They must first be configured, and
Web apps must be set up to access them through resource injection

In the task tree under Resources open the JDBC node and click JDBC Resources.

You should see some built-in resources listed.

Click New... to create a new resource:

The JNDI name must begin with "jdbc/".

Our example will be jdbc/cars.

Make sure this resource is connected with the CarPool. Click OK.

In order to use a data source, Java code can inject it in a manner similar to injecting beans.

All you need is the JNDI name of a data source and you can inject it as in this example:

   @Resource(name = "jdbc/cars")
   private DataSource carsSource;  // field is automagically instantiated
     ...
   Connection carsConnection = carsSource.getConnection();

This code obtains a database connection from the CarPool associated with jdbc/cars.

What to do with the connection is the subject of Introduction to JDBC.