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540

Appendix A

Servlet and JSP Quick Reference

  application 

Means that, in addition to being bound to a local variable, bean will be 

stored in shared 

ServletContext

 available through predefined 

application

 variable or by a call to 

getServletContext()

. 

  session 

Means that, in addition to being bound to a local variable, bean will be 

stored in 

HttpSession

 object associated with current request, where it 

can be retrieved with 

getValue

. 

  request 

Signifies that, in addition to being bound to a local variable, bean object 

should be placed in 

ServletRequest

 object for duration of current 

request, where it is available by means of the 

getAttribute

 method. 

Conditional Bean Creation

  A 

jsp:useBean

 element results in a new bean being instantiated only if 

no bean with the same 

id

 and 

scope

 can be found. If a bean with the 

same 

id

 and 

scope

 is found, the preexisting bean is simply bound to the 

variable referenced by 

id

.

  You can make 

jsp:setProperty

 statements conditional on new bean 

creation:

statements

A.14 Creating Custom JSP Tag Libraries

The Tag Handler Class

  Implement 

Tag

 interface by extending 

TagSupport

 (no tag body or tag 

body included verbatim) or 

BodyTagSupport

 (tag body is 

manipulated).

doStartTag

: code to run at beginning of tag

doEndTag

: code to run at end of tag

doAfterBody

: code to process tag body

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

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