Both
the applet and servlet can be set to acquire data from a
database ( or multiple database ) by utilizing a server
side script or process.
In
the previous section ( Connecting
the Graph to a Server Process. ) We saw how to connect
both the applet and servlet to a server side process. The
server side process can be written in any language of your
choice and as such can be written to acquire data from any
data source desired (databases, other processes, files etc.).
The
Graphing Software provides several methods by which data
can be acquired from databases. For a full discussion
on the various methods and Template Scripts please see
the
Tutorial Section.
Here
we will demonstrate how to create a Java Servlet which acquires
data from a single database and present the data in the
correct format to either the graph applet or graph servlet.
The
DatabaseServletbar
is designed to retrieve product sales data from a MySQL
database, from a table with the following structure,
Table
Name : SalesBar |
|
|
ProductName |
Character |
Year |
Integer |
Month |
Integer |
Value |
double |
Our
servlet will pick out the sales figures for three products
( ProductX, ProductY and ProductZ) and return the data in
the correct format for the graph.
The
method is as follows,
-
Set the output characteristics for the return data
-
Establish the database connection
-
Build the query statement and retrieve the database records
-
Process the database records and return the Data
-
All finished so close the database connection
The
full servlet code is contained in the DatabaseServletbar
file.
(Click
here to view the code).
As you
will see from the code the servlet connects to the database
via JDBC and as such it is essential to have the correct
JDBC drivers for your database. ( For further information
on JDBC drivers please see http://industry.java.sun.com/products/JDBC/drivers
)