Question

On a DataSource interface I found two methods to get Connection, with and without username and password paramenters.

Connection getConnection()
Connection getConnection(String username, String password)

Stated that I’d like to use a connection pool exposed as JNDI Resource from the server (tomcat) what differences are from the two methods?

Answer 1

Depending on the DataSource implementation, these two methods do different things. The first, with no arguments, simply obtains a Connection from the pool, configured with credentials configured when the DataSource was created. The second, which accepts new credentials, will obtain a Connection from the DataSource that was opened using those credentials, or it will create a new Connection with those credentials or — if the JDBC driver supports it — it will take an existing Connection and switch the credentials (I’m not sure if this is really even possible).

Unfortunately, the JavaDoc (http://docs.oracle.com/javase/7/docs/api/javax/sql/DataSource.html) does not really give you any insight to why one might call one versus the other. The obvious reason is because you want to connect using credentials other than those configured for the entire DataSource.

The default DataSource that Tomcat will configure for you is a BasicDataSource from the Apache commons-dbcp: this DataSource does not support the getConnection(String username, String password) method. Recent versions of Tomcat ship with tomcat-pool, which is an alternative DataSource implementation that does support this alternative mechanism (although the current documentation says it does not) if you set the alternateUsernameAllowed="true" attribute on your <Resource> element.

Tomcat-pool documentation: http://tomcat.apache.org/tomcat-7.0-doc/jdbc-pool.html