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Find this tutorial in: /usr/local/resin/webapps/resin-doc/db/tutorial/jdbc-basic
Try the Tutorial This tutorial describes the standard pattern for using a database in Resin.
Using a JDBC database is a three step process:
JDBC database access is based around the Factory pattern. With JDBC, javax.sql.DataSource is the Factory object and java.sql.Connection is the factory's generated object. The <database> configures the DataSource and stores it in the JNDI resource map. The servlet will retrieve the DataSource and use it as a factory to obtain Connection objects, the main workhorse for using databases.
In Resin 3.0, the <database> tag configures the database pool and driver and saves the connection factory (DataSource) in JNDI. JNDI is just a global lookup tree available to all classes, making it straightforward to separate resource configuration from the application code. The <driver> tag configures the database driver. The database vendor will make the driver classes available and describe the configuration variables. The thirdparty database page describes several important database configurations. The <type> tag is the most important driver configuration item. It specifies the main Java driver class. For many drivers, you will have a choice of different drivers following different internal JDBC APIs. If you have a choice, you should try the drivers in the following order, after checking your database vendor's recommendations:
The <url> specifies the location of the database. Each database driver will have a unique URL formal. In this case, the <url> specifies a directory for the database files. Other databases may specify a host and port. com.caucho.db.jca.ConnectionFactoryThe specific driver for this example, com.caucho.db.jca.ConnectionFactory is a simple database intended for examples and testing.
The servlet needs to locate the DataSource to use JDBC. The servlet needs to lookup the database pool's DataSource using JNDI. In the configuration above, the name "jdbc/basic" is shorthand for "java:comp/env/jdbc/basic". "java:comp/env" is a context containing configured resources. For example, "java:comp/env/jdbc/basic" is a JDBC resource in that context. Because the servlet only needs to look up the DataSource once, it will generally look it up in the init() method and store it as an instance variable. The DataSource is thread-safe, so it can be used simultaneously by any of the requesting threads.
The servlet checks see if the DataSource is already configured. If not, the assemble() method configures the DataSource itself using JNDI. Standard configuration
The most important pattern when using JDBC is the following try/finally block. All database access should follow this pattern. Because connections are pooled, it's vital to close the connection no matter what kind of exceptions may be thrown So the conn.close() must be in a finally block.
The full example splits the database access into two methods to clarify the roles. The service retrieves the output writer from the servlet response and wraps any checked exceptions in a ServletException. Splitting the servlet method simplifies the doQuery method, so it can concentrate on the database access.
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