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464

Chapter 18 JDBC and Database Connection Pooling

JDBC is most often used from servlets or regular desktop applications but

is also sometimes employed from applets. If you use JDBC from an applet,

remember that, to prevent hostile applets from browsing behind corporate

firewalls, browsers prevent applets from making network connections any 

where except to the server from which they were loaded. Consequently, to

use JDBC from applets, either the database server needs to reside on the

same machine as the HTTP server or you need to use a proxy server that

reroutes database requests to the actual server.

Establish the Connection

To make the actual network connection, pass the URL, the database user 

name, and the password to the 

getConnection

 method of the 

Driver 

Manager

 class, as illustrated in the following example. Note that

getConnection

 throws an 

SQLException

, so you need to use a 

try

/

catch

block. I'm omitting this block from the following example since the methods

in the following steps throw the same exception, and thus you typically use a

single 

try

/

catch

 block for all of them.

String username = "jay_debesee";

String password = "secret";

Connection connection =

DriverManager.getConnection(oracleURL, username, password);

An optional part of this step is to look up information about the database

by using the 

getMetaData

 method of 

Connection

. This method returns a

DatabaseMetaData

 object which has methods to let you discover the name

and version of the database itself (

getDatabaseProductName

, 

getData 

baseProductVersion

) or of the JDBC driver (

getDriverName

, 

get 

DriverVersion

). Here is an example:

DatabaseMetaData dbMetaData = connection.getMetaData();

String productName = 

dbMetaData.getDatabaseProductName();

System.out.println("Database: " + productName);

String productVersion = 

dbMetaData.getDatabaseProductVersion();

System.out.println("Version: " + productVersion);

Other useful methods in the 

Connection

 class include 

prepareState 

ment

 (create a 

PreparedStatement

; discussed in Section 18.6), 

prepare 

Call

 (create a 

CallableStatement

), 

rollback

 (undo statements since last

commit

), 

commit

 (finalize operations since last 

commit

), 

close

 (terminate

connection), and 

isClosed

 (has the connection either timed out or been

explicitly closed?).

Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.

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