4.1.4 Connecting to a Data Source

In the previous section, a DataSource object, vds, was given properties and bound to the logical name AcmeDB. The following code fragment shows application code that uses this logical name to connect to the database that vds represented. The code then uses the connection to print lists with the name and title of each member of the sales and customer service departments.

Context ctx = new InitialContext();
DataSource ds = (DataSource)ctx.lookup("jdbc/AcmeDB");
Connection con = ds.getConnection("genius", "abracadabra");
con.setAutoCommit(false);
PreparedStatement pstmt = con.prepareStatement(
"SELECT NAME, TITLE FROM PERSONNEL WHERE DEPT = ?");
pstmt.setString(1, "SALES");
ResultSet rs = pstmt.executeQuery();
System.out.println("Sales Department:");
while (rs.next()) {
String name = rs.getString("NAME");
String title = rs.getString("TITLE");
System.out.println(name + " ; ;" + title);
}
pstmt.setString(1, "CUST_SERVICE");
ResultSet rs = pstmt.executeQuery();
System.out.println("Customer Service Department:");
while (rs.next()) {
String name = rs.getString("NAME");
String title = rs.getString("TITLE");
System.out.println(name + " ; ;" + title);
}
rs.close();
pstmt.close();
con.close();
The first two lines use JNDI API; the third line uses DataSource API. After the first line creates an instance of javax.naming.Context for the initial naming context, the second line calls the method lookup on it to get the DataSource object associated with jdbc/AcmeDB. Recall that in the previous code fragment, the last line of code associated jdbc/AcmeDB with vds, so the object returned by the lookup method refers to the same DataSource object that vds represented. However, the return value for the method lookup is a reference to a Java Object, the most generic of objects, so it must be cast to the more narrow DataSource before it can be assigned to the DataSource variable ds.
At this point ds refers to the same data source that vds referred to previously, the database my_database on the server my_database_server. Therefore, in the third line of code, calling the method DataSource.getConnection on ds and supplying it with a user name and password is enough to create a connection to my_database.
The rest of the code fragment uses a single transaction to execute two queries and print the results of each query. The DataSource implementation in this case is a basic implementation included with the JDBC driver. If the DataSource class had been implemented to work with an XADataSource class, and the preceding code example was executed in the context of a distributed transaction, the code could not have called the method Connection.commit. It also would not have set the auto-commit mode to false because that would have been unnecessary. The default for newly-created connections that can participate in distributed transactions is to have auto-commit mode turned off. The next section will discuss the three broad categories of DataSource implementations.
In addition to the version of getConnection that takes a user name and password, the DataSource interface provides a version of the method DataSource.getConnection that takes no parameters. It is available for situations where a data source does not require a user name and password because it uses a different security mechanism or where a data source does not restrict access.