Generally, the JDBC API enables users to access virtually any kind of tabular data source, such as spreadsheets or flat files, from a Java application. It also provides connectivity to a wide scope of Oracle databases. One of the most important advantages of using JDBC is that it allows users to access any kind of relational database in the same way with code, which means that the user can develop one program with the same code to access either an Oracle database or a MySQL database without code modification.
The JDBC 3.0 and JDBC 4.0 specifications contain additional features, such as extensions to sup-port various data types, metadata components and improvements to some interfaces.
The JDBC API is composed of a set of classes and interfaces used to interact with databases from Java applications. As we discussed in Chapter 3, the basic components of JDBC are located in the package java.sql, and the Standard Extension of JDBC, which provides additional fea-tures, such as the Java Naming and Directory Interface and Java Transaction Service, is in the javax.sql package.
The first step to build a Java database application is to load and register a JDBC driver. Two important components, DriverManager and Driver, are used for this process. As we discussed in Chapter 4, the Driver class contains six methods, and one of the most important is the con-nect() method, which is used to connect to the database. When using the Driver class, a point to be noted is that most methods defined in the Driver class should never be called directly; instead, they should be called via the DriverManager class methods.
The DriverManager class is a set of utility functions that work with the Driver methods and manage multiple JDBC drivers by keeping them as a list of loaded drivers. Although loading and registering a driver are two steps, only one method call is necessary to perform these two opera-tions. The operational sequence of loading and registering a JDBC driver is:
1) Call class methods in the DriverManager class to load the driver into the Java interpreter.
2) Register the driver using the registerDriver() method.
When loaded, the driver will execute the DriverManager.registerDriver() method to register itself. The previous two operations will never be performed until a method in the
DriverManager is executed, which means that even if both operations have been coded in an application, the driver cannot be loaded and registered until a method such as connect() is first executed.
To load and register an Oracle JDBC driver, two popular methods can be used:
1) Use the Class.forName() method: Class.forName(“oracle.jdbc.OracleDriver”);
2) Create a new instance of the Driver class: Driver oraDriver = new oracle. jdbc.OracleDriver;
Relatively speaking, the first method is more professional, since the driver is both loaded and registered when a valid method in the DriverManager class is executed. The second method cannot guarantee that the driver has been registered by using the DriverManager. We prefer to use the first method in this application.