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32

Chapter 2 First Servlets

HTML 3.2 and 4.0 specifications require it. I strongly discourage this prac 

tice. The advantage of the 

DOCTYPE

 line is that it tells HTML validators

which version of HTML you are using, so they know which specification to

check your document against. These validators are very valuable debugging

services, helping you catch HTML syntax errors that your browser guesses

well on, but that other browsers will have trouble displaying. The two most

popular on line validators are the ones from the World Wide Web Consor 

tium (

http://validator.w3.org/

) and from the Web Design Group

(

http://www.htmlhelp.com/tools/validator/

). They let you submit a

URL, then they retrieve the page, check the syntax against the formal HTML

specification, and report any errors to you. Since a servlet that generates

HTML looks like a regular Web page to visitors, it can be validated in the

normal manner unless it requires 

POST

 data to return its result. Remember

that 

GET

 data is attached to the URL, so you can submit a URL that includes

GET

 data to the validators.

Core Approach

Use an HTML validator to check the syntax of pages that your servlets 

generate.

Admittedly it is a bit cumbersome to generate HTML with 

println

 state 

ments, especially long tedious lines like the 

DOCTYPE

 declaration. Some people

address this problem by writing detailed HTML generation utilities in Java,

then use them throughout their servlets. I'm skeptical of the utility of an exten 

sive library for this. First and foremost, the inconvenience of generating

HTML programmatically is one of the main problems addressed by JavaServer

Pages (discussed in the second part of this book). JSP is a better solution, so

don't waste effort building a complex HTML generation package. Second,

HTML generation routines can be cumbersome and tend not to support the

full range of HTML attributes (

CLASS

 and 

ID

 for style sheets, JavaScript event

handlers, table cell background colors, and so forth). Despite the questionable

value of a full blown HTML generation library, if you find you're repeating the

same constructs many times, you might as well create a simple utility file that

simplifies those constructs. For standard servlets, there are two parts of the

Web page (

DOCTYPE

 and 

HEAD

) that are unlikely to change and thus could ben 

efit from being incorporated into a simple utility file. These are shown in List 

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

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