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10.2 JSP Expressions

session

, the

HttpSession

 associated with the request (unless

disabled with the

session

 attribute of the

page

 directive   see

Section 11.4)

out

, the

PrintWriter

 (a buffered version called

JspWriter

used to send output to the client

Here is an example:

Your hostname: <%= request.getRemoteHost() %>

XML Syntax for Expressions

XML authors can use the following alternative syntax for JSP expressions:

Java Expression

Note that XML elements, unlike HTML ones, are case sensitive, so be

sure to use

jsp:expression

 in lower case.

Using Expressions as Attribute Values

As we will see later, JSP includes a number of elements that use XML syntax

to specify various parameters. For example, the following example passes

"Marty"

 to the

setFirstName

 method of the object bound to the

author

variable. Don't worry if you don't understand the details of this code; it is dis

cussed in detail in Chapter 13 (Using JavaBeans with JSP). My purpose here

is simply to point out the use of the

name

property

, and

value

 attributes.

property="firstName"

value="Marty" />

Most attributes require the value to be a fixed string enclosed in either sin

gle or double quotes, as in the example above. A few attributes, however, per

mit you to use a JSP expression that is computed at request time. The

value

attribute of

jsp:setProperty

 is one such example, so the following code is

perfectly legal:

property="id"

value='<%= "UserID" + Math.random() %>' />

Table 10.1 lists the attributes that permit a request time value as in this

example.

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