What does Tomcat do under the hood to give you an implementation of DataSource

Question

From JNDI Resources HOW-TO

<Context ...>
  ...
  <Resource name="jdbc/EmployeeDB"
            auth="Container"
            type="javax.sql.DataSource"
            username="dbusername"
            password="dbpassword"
            driverClassName="org.hsql.jdbcDriver"
            url="jdbc:HypersonicSQL:database"
            maxActive="8"
            maxIdle="4"/>
  ...
</Context>

The type is javax.sql.DataSource and this is an interface.

The code below retrieves an instance of DataSource and get a connection out of it.

Context initCtx = new InitialContext();
Context envCtx = (Context) initCtx.lookup("java:comp/env");
DataSource ds = (DataSource)
  envCtx.lookup("jdbc/EmployeeDB");

Connection conn = ds.getConnection();
... use this connection to access the database ...
conn.close();

From this Stackoverflow answer, it says the actual implementation of DataSource is up to the database vendor.

So in this example, does Tomcat use driverClassName="org.hsql.jdbcDriver" to return an implementation of DataSource ?

Answer 1

Tomcat has a connection pool implementation. This connection pool has an implementation of the interface DataSource. And this implementation uses the specified driver class (org.hsql.jdbcDriver) in order to open connections to the database.