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An Introduction to JDBC

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driver can communicate with multiple ODBC drivers. Each of the ODBC

drivers execute SQL statements for specific databases. The results are

sent back up the chain as before.

Fig.1

The JDBC/ODBC bridge was developed to take advantage of the large

number of ODBC enable data sources. The bridge converts JDBC calls to

ODBC calls and passes them to the appropriate driver for the backend

database. The advantage of this scheme is that applications can access

data from multiple vendors. However, the performance of a JDBC/ODBC

bridge is lower than a JDBC driver alone due to the added overhead. A

database call must be translated from JDBC to ODBC to a native API.

Fewer operations are required to use a JDBC driver without a bridge.

In Fig.2, the steps to access a database using a JDBC driver from an

applet are shown. The Gwe JDBC driver is used with the Mysql database.

The JDBC driver classes are first downloaded from the WWW host. Next,

the applet logic passes a JDBC call to a driver manager which in turns

passes the call to a JDBC driver. The JDBC driver opens a TCP/IP

connection with the Mysql database server. Data is transferred back

and forth via the connection. When database processing is complete,

the connection is closed.

Fig.2

The JDBC API can be used in applets and stand-alone applications. In

addition to the usual restrictions for applets, only connections from

a server from which the applet was downloaded are accepted. If the web

server and database server are not on the same machine, then the web

server must run a proxy service to route the database traffic. Stand

alone applications can give access to local information and remote

servers.

Installation:

The installation of the JDBC driver for the Mysql database is simple

and can be downloaded from Gwe Technologies at http://www.gwe.co.uk.

The copyright statement allows the redistribution of source and

binary, but is not identitical to the GNU license. Download the file -

exgweMysqlJDBC.0.9.2-src.tar.gz. It contains the source and class

files for Gwe Mysql JDBC driver.

The use of JDBC requires access to java.sql classes which were not

available in the pre 1.1 Java Development Kit. These classes have been