Prentice Hall and Sun Microsystems. Personal use only; do not redistribute.
168
Chapter 7 Generating the Server Response: HTTP Response Headers
7.5 Using Servlets to Generate GIF 
Images
Although servlets often generate HTML output, they certainly don't always
do so. For example, Section 11.2 (The contentType Attribute) shows a JSP
page (which gets translated into a servlet) that builds Excel spreadsheets and
returns them to the client. Here, I'll show you how to generate GIF images.
First, let me summarize the two main steps servlets have to perform in
order to build multimedia content. First, they have to set the 
Content Type
response header by using the 
setContentType
 method of 
HttpServlet 
Response
. Second, they have to send the output in the appropriate format.
This format varies among document types, of course, but in most cases you
use send binary data, not strings as with HTML documents. Consequently,
servlets will usually get the raw output stream by using the 
getOutput 
Stream
 method, rather than getting a 
PrintWriter
 by using 
getWriter
.
Putting these two points together, servlets that generate non HTML content
usually have a section of their 
doGet
 or 
doPost
 method that looks like this:
response.setContentType("type/subtype");
OutputStream out = response.getOutputStream();
Those are the two general steps required to build non HTML content.
Next, let's look at the specific steps required to generate GIF images.
1. Create an 
Image
.
You create an 
Image
 object by using the 
createImage
 method 
of the 
Component
 class. Since server side programs should not 
actually open any windows on the screen, they need to explicitly 
tell the system to create a native window system object, a pro 
cess that normally occurs automatically when a window pops 
up. The 
addNotify
 method accomplishes this task. Putting this 
all together, here is the normal process:
Frame f = new Frame();
f.addNotify();
int width = ...;
int height = ...;
Image img = f.createImage(width, height);
Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.
Servlet and JSP training courses by book's author: courses.coreservlets.com.






footer




 

 

 

 

 Home | About Us | Network | Services | Support | FAQ | Control Panel | Order Online | Sitemap | Contact

jsp web hosting

 

Our partners: PHP: Hypertext Preprocessor Best Web Hosting Java Web Hosting Jsp Web Hosting Cheapest Web Hosting

Visionwebhosting.net Business web hosting division of Web Design Plus. All rights reserved