ensures that the drivers will perform as expected. Essentially, the developer who has JDBC drivers for a certain database does not need to worry about changing the code for the Java program if a different type of database is used (assuming that the JDBC driver for the other database is available). This is especially useful in the scenario of distributed databases. Figure 1.1 The architecture of the JDBC. The JDBC uses a URL syntax for specifying a database. For example, a connection to a mSQL database, which was used to develop some of the Java applets in this book, is: jdbc:msql://mydatabase.server.com:1112/testdb This statement specifies the transport to use (jdbc), the database type (msql), the server name, the port (1112), and the database to connect to (testdb). We ll discuss specifying a database more thoroughly in Chapter 3. The data types in SQL are mapped into native Java types whenever possible. When a native type is not present in Java, a class is available for retrieving data of that type. Consider, for example, the Date type in the JDBC. A developer can assign a date field in a database to a JDBC Date class, after which the developer can use the methods in the Date class to display or perform operations. The JDBC also includes support for binary large objects, or BLOB data types; you can retreive and store images, sound, documents, and other binary data in a database with the JDBC. In Chapter 6, we ll cover the SQL data types and their mapping into Java/JDBC, as well object-relational mapping. ODBC s Part In The JDBC The JDBC and ODBC share a common parent: Both are based on the same X/OPEN call level interface for SQL. Though there are JDBC drivers emerging for many databases, you can write database-aware Java programs using existing ODBC drivers. In fact, Javasoft and Intersolv have written a JDBC driver the JDBC-ODBC Bridge that allows developers to use exisiting ODBC drivers in Java programs. Figure 1.2 shows the place of the JDBC-ODBC Bridge in the overall architecture of the JDBC. However, the JDBC-ODBC Bridge requires pre-installation on the client, or wherever the Java program is actually running, because the Bridge must make native method calls to do the translation from ODBC to JDBC. This pre-installation issue is also true for JDBC drivers that use native methods. Only 100 percent Java JDBC drivers can be downloaded across a network with a Java applet, thus requiring no pre-installation of the driver.
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