Recipe 21.2 Configuring a DataSource in Tomcat

Problem

You want to configure a javax.sql.DataSource for use in a servlet with the Tomcat web container.

Solution

Create a resource element in Tomcat's server.xml file and an associated resource-ref element in the web.xml deployment descriptor.

Discussion

Tomcat makes it easy to set up a connection pool so that servlets and JSPs can efficiently share database connections. In web sites that have many simultaneous users, a connection pool improves efficiency by sharing existing database connections, rather than creating a new connection and tearing it down every time an application has to use the database.

Another benefit of configuring a connection pool is that you can change the database system that a servlet or JSP is using without touching the Java code, because the database resource is configured outside of the servlet or JSP.

Here are the steps for configuring a DataSource with Tomcat:

Create a Resource and a ResourceParams element in server.xml, or in the XML file that you have placed in Tomcat's webapps directory. These elements describe the JNDI object you are creating in order to provide your servlets or JSPs with a DataSource.
Add a resource-ref element to web.xml, which allows the components in the associated web application to access the configured DataSource.

Example 21-2 shows the Resource and a ResourceParams elements in server.xml. This example describes a DataSource that connects with an Oracle 8i database.

Example 21-2. The resource element in server.xml

<Resource name="jdbc/oracle-8i-athletes" scope=
  "Shareable" type="javax.sql.DataSource" auth=
    "Container" description="Home Oracle 8i Personal Edition"/>

    <ResourceParams name="jdbc/oracle-8i-athletes">

      <parameter>
          <name>driverClassName</name>
          <value>oracle.jdbc.driver.OracleDriver</value>
      </parameter>

      <parameter>
          <name>url</name>
          <value>jdbc:oracle:thin:@192.168.0.2:1521:ORCL</value>
      </parameter>

          <parameter>
          <name>username</name>
          <value>scott</value>
      </parameter>

          <parameter>
          <name>password</name>
          <value>tiger</value>
      </parameter>

</ResourceParams>

Create a Resource and ResourceParams element for each database that your application uses. Example 21-3 shows the resource-ref element associated with the Resource specified by Example 21-2.

Example 21-3. A resource-ref element specifies a DataSource in web.xml

<!-- top of web.xml file -->
<resource-ref>

    <res-ref-name>jdbc/oracle-8i-athletes</res-ref-name>

    <res-type>javax.sql.DataSource</res-type>

    <res-auth>Container</res-auth>

</resource-ref>
<!-- rest of web.xml file -->

The JNDI path to this DataSource, which you use in a JNDI lookup (see the next recipe), is jdbc/oracle-8i-athletes.