JavaServer Pages, 3rd Edition

The DataSource Interface and JDBC Drivers

Before we get started with the examples, let’s look at how to identify the database you want to access. The JSTL actions can find this information in many different ways, to make the simple scenario simple and the more complex ones possible. In all cases, though, they get access to the database through an instance of a JDBC interface named javax.sql.DataSource.

The DataSource interface is part of the Java 2 Standard Edition (J2SE) 1.4, and for prior versions of the J2SE, it’s available in the JDBC 2.0 Optional Package. To access a database, a connection to the database must first be established. Opening a database connection is very time-consuming. A nice thing with a DataSource is that it can represent something called a connection pool. Connection pools are described in more detail in Chapter 24, but it’s exactly what it sounds like: a pool of database connections that can be shared by multiple clients. With a connection pool, a connection to the database is opened once and stays open until the application is shut down. When a database action needs a connection, it gets it from the pool through the DataSource object and uses it to execute one or more SQL statements. When the action closes the connection, the connection is returned to the pool where it can be picked up by the next action that needs it.

In addition to the DataSource, the JDBC API contains other classes and interfaces that allow a Java application to process SQL statements ...