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242

Chapter 10 JSP Scripting Elements

When converted to a servlet by the JSP engine, this fragment will result in

something similar to the following.

if (Math.random() < 0.5) { 

  out.println("Have a nice day!");

} else { 

  out.println("Have a lousy day!");

}

Special Scriptlet Syntax

There are two special constructs you should take note of. First, if you want to

use the characters 

%>

 inside a scriptlet, enter 

%\>

 instead. Second, the XML

equivalent of 

<% Code %>

 is 

Code

The two forms are treated identically by JSP engines.

10.4 JSP Declarations

A JSP declaration lets you define methods or fields that get inserted into the

main body of the servlet class (outside of the 

_jspService

 method that is

called by 

service

 to process the request). A declaration has the following form:

<%! Java Code %>

Since declarations do not generate any output, they are normally used in

conjunction with JSP expressions or scriptlets. For example, here is a JSP

fragment that prints the number of times the current page has been

requested since the server was booted (or the servlet class was changed and

reloaded). Recall that multiple client requests to the same servlet result only

in multiple threads calling the 

service

 method of a single servlet instance.

They do not result in the creation of multiple servlet instances except possibly

when the servlet implements 

SingleThreadModel

. For a discussion of 

Sin 

gleThreadModel

, see Section 2.6 (The Servlet Life Cycle) and Section 11.3

(The isThreadSafe Attribute). Thus, instance variables (fields) of a servlet are

shared by multiple requests and 

accessCount

 does not have to be declared

static

 below.

<%! private int accessCount = 0; %>

Accesses to page since server reboot: 

<%= ++accessCount %>

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

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