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76

Chapter 3 Handling the Client Request: Form Data

Listing 3.6 shows the servlet that processes the data from the HTML form.

When the  Preview  button is pressed, the servlet first reads the font and color

parameters. Before using any of the parameters, it checks to see if the value is

null

 (i.e., there is an error in the HTML form and thus the parameter is missing)

or is an empty string (i.e., the user erased the default value but did not enter any 

thing in its place). The servlet uses a default value appropriate to each parameter

in such a case. Parameters that represent numeric values are passed to

Integer.parseInt

. To guard against the possibility of improperly formatted

numbers supplied by the user, this 

Integer.parseInt

 call is placed inside a

try

/

catch

 block that supplies a default value when the parsing fails. Although it

may seem a bit tedious to handle these cases, it generally is not too much work if

you make use of some utility methods such as 

replaceIfMissing

 and 

repla 

ceIfMissingOrDefault

 in Listing 3.6. Tedious or not, users will sometimes

overlook certain fields or misunderstand the required field format, so it is critical

that your servlet handle malformed parameters gracefully and that you test it with

both properly formatted and improperly formatted data.

Core Approach

Design your servlets to gracefully handle missing or improperly formatted 

parameters. Test them with malformed data as well as with data in the 

expected format.

Once the servlet has meaningful values for each of the font and color

parameters, it builds a cascading style sheet out of them. If you are unfamiliar

with style sheets, they are a standard way of specifying the font faces, font

sizes, colors, indentation, and other formatting information in an HTML 4.0

Web page. Style sheets are usually placed in a separate file so that several

Web pages at a site can share the same style sheet, but in this case it is

more convenient to embed the style information directly in the page by

using the

STYLE

 element. For more information on style sheets, see

http://www.w3.org/TR/REC CSS1

.

After creating the style sheet, the servlet places the job applicant's name,

job title, and e mail address centered under each other at the top of the page.

The heading font is used for these lines, and the e mail address is placed

inside a 

mailto:

 hypertext link so that prospective employers can contact

the applicant directly by clicking on the address. The programming languages

specified in the 

languages

 parameter are parsed using 

StringTokenizer

(assuming spaces and/or commas are used to separate the language names)

and placed in a bulleted list beneath a  Programming Languages  heading.

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

Servlet and JSP training courses by book's author: courses.coreservlets.com.