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Tomcat: The Definitive Guide, 2nd Edition by Ian F. Darwin, Jason Brittain

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Accessing JNDI and JDBC Resources

Many web applications will need access to a relational database. To make web applications portable, the Java EE specification requires a database-independent description in the web applications's WEB-INF/web.xml file and allows the container developer to provide a means for providing the database-dependant details; Tomcat developers naturally chose to put this in the server.xml file. Then, the JNDI is used to locate database sources and other resources. Each of these resources, when accessed through JNDI, is referred to as a context.

Warning

Watch out! A JNDI context is completely different than a Tomcat context (which is a synonym for "web application"). In fact, JNDI contexts and Tomcat webapp contexts are completely unrelated.

JDBC DataSources

You probably know whether your web application requires a JDBC datasource. If you're not sure, look in the web.xml file for the application, and search for something like this:

<resource-ref>
  <description>
    The database DataSource for the Acme web application.
  </description>
  <res-ref-name>jdbc/JabaDotDB</res-ref-name>
  <res-type>javax.sql.DataSource</res-type>
  <res-auth>Container</res-auth>
</resource-ref>

As an alternative, if you have the Java source code available, you can look for something like this:

Context ctx = new InitialContext(  );
DataSource ds = (DataSource)
  ctx.lookup("java:comp/env/jdbc/JabaDotDB");

Connection conn = ds.getConnection(  );
... Java code that accesses the database ...
conn.close(  );

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