JDBC

JDBC Tutorial: http://java.sun.com/docs/books/tutorial/jdbc/
Hibernate: http://www.hibernate.org/
JDO: http://www.jdocentral.com/index.html
EJB: http://java.sun.com/developer/onlineTraining/EJBIntro/EJBIntro.html

Intro To JDBC

JDBC stands for Java Database Connectivity, and it's the API supplied by Sun for access to databases. The JDBC API is defined in two packages: java.sql, and javax.sql. java.sql contains the "client" JDBC API whereas javax.sql contains more server-oriented extensions, like connection pooling. JDBC has gone through several revisions. The current version is JDBC 3.0, but a lot of basic functionality has remained the same since JDBC 1.0. JDBC provides a common API for database access, regardless of the particular database server you're using. It accomplishes this using a component-oriented architecture. Database vendors (e.g. Oracle, SQL Server, Sybase, MySQL, PostgreSQL, etc...) supply a driver for JDBC. Once you load the right driver, you're off to the races and can continue working with just the JDBC API. JDBC is a fairly thin interface, in that it allows you mainly to send SQL statements to a particular database. If you are interested in more generic object-relational mapping, take a look at Hibernate (highly recommended) or JDO, or EJB. The basic features of JDBC are:

Retrieving data
Creating data
Transactions

Loading a JDBC Driver and Establishing a Connection

Loading a JDBC driver is done using reflection. You pass the name of the driver class and the appropriate driver gets loaded for you by the Java Runtime. This allows anyone to write a JDBC driver than can be transparently loaded into an application. As long as you conform to the interfaces, you too can write your own JDBC driver, say for a database using simple files or a database that stores data in XML (acually, the latter already exists I believe). For demo purposes, Sun supplies a JDBC driver that connects to Microsoft's ODBC (if you want to connect a real application to, say, SQL Server, don't use this driver. Use the driver supplied by microsoft, or a commercial driver). The following line of code will load the JDBC-ODBC bridge driver:

Class.forName("sun.jdbc.odbc.JdbcOdbcDriver").newInstance();

To connect to an Oracle database using the Oracle Thin-Client JDBC driver, try this:

DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());

Class.forName("oracle.jdbc.driver.OracleDriver").newInstance();

To get a connection, you specify the name of the ODBC DSN, the username, and the password:

Connection con = DriverManager.getConnection("jdbc:odbc:MyAccessDB, "sa", "mypassword");

The format of the first string will vary from driver to driver... For example, here is the call using the Oracle Thin-Client JDBC Driver from Oracle:

Connection conn = DriverManager.getConnection("jdbc:oracle:thin:@//myhost:1521/orcl", "scott", "tiger");

Once you have a connection, you can use that connection to access the database, i.e. send SQL command, and start/commit/rollback transactions!