Prentice Hall and Sun Microsystems. Personal use only; do not redistribute.

10.1 Scripting Elements

233

Aside from the regular HTML, there are three main types of JSP con 

structs that you embed in a page: scripting elements, directives, and actions.

Scripting elements let you specify Java code that will become part of the

resultant servlet, directives let you control the overall structure of the servlet,

and actions let you specify existing components that should be used and oth 

erwise control the behavior of the JSP engine. To simplify the scripting ele 

ments, you have access to a number of predefined variables, such as 

request

in the code snippet just shown (see Section 10.5 for more details). Scripting

elements are covered in this chapter, and directives and actions are explained

in the following chapters. You can also refer to Appendix  (Servlet and JSP

Quick Reference) for a thumbnail guide summarizing JSP syntax.

This book covers versions 1.0 and 1.1 of the JavaServer Pages specification.

JSP changed dramatically from version 0.92 to version 1.0, and although

these changes are very much for the better, you should note that newer JSP

pages are almost totally incompatible with the early 0.92 JSP engines, and

older JSP pages are equally incompatible with 1.0 JSP engines. The changes

from version 1.0 to 1.1 are much less dramatic: the main additions in version

1.1 are the ability to portably define new tags and the use of the servlet 2.2

specification for the underlying servlets. JSP 1.1 pages that do not use custom

tags or explicitly call 2.2 specific statements are compatible with JSP 1.0

engines, and JSP 1.0 pages are totally upward compatible with JSP 1.1

engines.

10.1 Scripting Elements

JSP scripting elements let you insert code into the servlet that will be gener 

ated from the JSP page. There are three forms: 

1. Expressions of the form 

<%= expression %>

, which are evalu 

ated and inserted into the servlet's output

2. Scriptlets of the form 

<% code %>

, which are inserted into the 

servlet's 

_jspService

 method (called by 

service

)

3. Declarations of the form 

<%! code %>

, which are inserted into 

the body of the servlet class, outside of any existing methods

Each of these scripting elements is described in more detail in the follow 

ing sections. 

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

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