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334

Chapter 14 Creating Custom JSP Tag Libraries

14.6 Manipulating the Tag Body

The 

csajsp:prime

 element (Section 14.3) ignored any body content, the

csajsp:heading

 element (Section 14.4) used body content, and the 

csa 

jsp:debug

 element (Section 14.5) ignored or used it depending on a request

time parameter. The common thread among these elements is that the tag

body was never modified; it was either ignored or included verbatim (after

JSP translation). This section shows you how to process the tag body.

The Tag Handler Class

Up to this point, all of the tag handlers have extended the 

TagSupport

 class.

This is a good standard starting point, as it implements the required 

Tag

interface and performs a number of useful setup operations like storing the

PageContext

 reference in the 

pageContext

 field. However, 

TagSupport

 is

not powerful enough for tag implementations that need to manipulate their

body content, and 

BodyTagSupport

 should be used instead. 

BodyTagSupport

 extends 

TagSupport

, so the 

doStartTag

 and 

doEndTag

methods are used in the same way as before. The two important new meth 

ods defined by 

BodyTagSupport

 are:

1.

doAfterBody

, a method that you should override to handle the 

manipulation of the tag body. This method should normally 

return 

SKIP_BODY

 when it is done, indicating that no further 

body processing should be performed.

2.

getBodyContent

, a method that returns an object of type 

BodyContent

 that encapsulates information about the tag body.

The 

BodyContent

 class has three important methods:

1.

getEnclosingWriter

, a method that returns the 

JspWriter

being used by 

doStartTag

 and 

doEndTag

.

2.

getReader

, a method that returns a 

Reader

 that can read the 

tag's body. 

3.

getString

, a method that returns a 

String

 containing the 

entire tag body.

In Section 3.4 (Example: Reading All Parameters), we saw a static 

filter

method that would take a string and replace 

<

, 

>

, 

"

, and 

&

 with 

<

, 

>

,

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