Why do we use a DataSource instead of a DriverManager?
I am reading the Java JDBC specification (vr. 4) and I encountred this statement:
DataSource — this interface was introduced in the JDBC 2.0 Optional Package API. It is preferred over DriverManager because it allows details about the underlying data source to be transparent to the application
What I am trying to understand is what the difference is between a Connection and a DataSource, and why it exists. I mean, the block above says that the details about a datasource is transparent to the application, but wouldn't externalizing database properties such as username, password, url etc in a property file and then use DriverManager work in the same way?
And is the DataSource interface created only to have a common way of returning connections that can be pooled etc? In Java EE, does the application server implement this interface and the applications deployed to have a reference to a datasource instead of a connection?
Answer
Better scalability and maintenance
For DriverManager you need to know all the details (host, port, username, password, driver class) to connect to DB and to get connections. Externalizing those in a properties file doesn't change anything about the fact that you need to know them.
Using a DataSource you only need to know the JNDI name. The AppServer cares about the details and is not configured by the client application's vendor, but by an admin where the application is hosted.
Scalability:
Suppose you need to create connections yourself, how would you deal with changing load, sometime you have 10 users sometime you have 1000, you can't just get a connection whenever you need one and later 'release' it so the Database server does not get out of connections, which leads you to connection pooling. DriverManager does not provide it, DataSource does.
If you are going to program a connection pool yourself then you have to use DriverManager, otherwise go with DataSource.