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324

Chapter 14 Creating Custom JSP Tag Libraries

In this section, we see how to define tags that use their body content, and

are thus used in the following manner:

body

The Tag Handler Class

In the previous examples, the tag handlers defined a 

doStartTag

 method

that returned 

SKIP_BODY

. To instruct the system to make use of the body that

occurs between the new element's start and end tags, your 

doStartTag

method should return 

EVAL_BODY_INCLUDE

 instead. The body content can

contain JSP scripting elements, directives, and actions, just like the rest of the

page. The JSP constructs are translated into servlet code at page translation

time, and that code is invoked at request time.

If you make use of a tag body, then you might want to take some action

after the body as well as before it. Use the 

doEndTag

 method to specify this

action. In almost all cases, you want to continue with the rest of the page after

finishing with your tag, so the 

doEndTag

 method should return 

EVAL_PAGE

. If

you want to abort the processing of the rest of the page, you can return

SKIP_PAGE

 instead.

Listing 14.10 defines a tag for a heading element that is more flexible than

the standard HTML 

H1

 through 

H6

 elements. This new element allows a pre 

cise font size, a list of preferred font names (the first entry that is available on

the client system will be used), a foreground color, a background color, a bor 

der, and an alignment (

LEFT

, 

CENTER

, 

RIGHT

). Only the alignment capability

is available with the 

H1

 through 

H6

 elements. The heading is implemented

through use of a one cell table enclosing a 

SPAN

 element that has embedded

style sheet attributes. The 

doStartTag

 method generates the 

TABLE

 and

SPAN

 start tags, then returns 

EVAL_BODY_INCLUDE

 to instruct the system to

include the tag body. The 

doEndTag

 method generates the

 and

 tags, then returns 

EVAL_PAGE

 to continue with normal page pro 

cessing. Various 

setAttributeName

 methods are used to handle the

attributes like 

bgColor

 and 

fontSize

. 

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