Java Reference
In-Depth Information
Expressions
Expressions are similar to scriptlets, but they evaluate a regular Java expression and return a result,
which is a
String
or something convertible to a
String
, to the client as part of the response. The
general syntax is as follows:
<%= expression %>
Scriptlets
Scriptlets are blocks of Java code surrounded within the
<%
and
%>
delimiters to create dynamic
content. Listing 2-19 illustrates the usage of a declaration with a scriptlet and expression.
Listing 2-19. Usage of Declaration, Scriptlet, and Expression
1.<%!
2.public String hello() {
3.String msg = "Hello World";
4.return msg;
5.}
6.%>
7.Message from <b>Scriptlet</b>:
<%hello();%>
<br/>
8.Message from <b>Expression</b>:
<%=hello() %>
Lines 1 to 6
: These lines contain a JSP declaration that declares a
hello()
method. Line 1 is the start tag, and line 6 is the end tag of the declaration.
Line 7
: The
hello()
method declared in lines 1 to 6 is used in an expression
on line 7.
Figure
2-27
illustrates the usage of declaration, scriptlets and expression.
Figure 2-27.
Using the declaration, scriptlet, and expression
Implicit Objects
In a web application, multiple web components collaborate with each other and share information by
means of objects that are maintained as attributes of four scope objects. You access these attributes
by using the
getAttribute
and
setAttribute
methods of the class representing the scope. Table
2-4
lists the scope objects.
