« The engineers at Sun Microsystems make life a bit easier for the JSP programmer by providing the programmer access to predefined environment objects called implicit objects. These objects are accessible from JSP expressions and JSP scriptlets. You read about these objects later in this chapter. JSP Declarations As with any programming language, JSP uses variables to hold program data or code that performs various tasks. One JSP feature that makes variables or program code known to the JSP page is called a JSP declaration. JSP declarations have the following format: In Listing 4-2 you see a simple page with a JSP declaration and expression. Listing 4-2: Simple JSP page with a declaration and expression Simple JSP Declaration Example
int sumOfFirstIntegers = toInteger * (toInteger + 1 ) / 2; int sumByLoop = 0 ; for (int counter = 1; counter The sum of integers from 1 to by loop is: Notice that Listing 4-4 uses pieces of Java code as opposed to an entire method. Changing Listing 4-4 to use a declaration causes the JSP translator to generate an error, as shown in Listing 4-5. Listing 4-5: Tomcat reacts to using a JSP declaration where a scriptlet is called for Error: 500 Location: /examples/jsp/loutest/loutest.jspInternal Servlet Error: org.apache.jasper.JasperException: Unable to compile class forJSPD:tomcat32worklocalhost_8080%2Fexamples_0002fjsp_0002floutest_0002floutest_0002ejsploutest_jsp_0.java:24: Typeexpected. for (int counter = 1; counter »

Coding and Invoking a Method

<%-- Here's a variable and method declaration --%> <%! int toInteger = 100 ; int sumOfFirstIntegers = addIntegers( 100 ) ; public int addIntegers( int to ) { return to * (to + 1) / 2 ; }%>

The sum of integers from 1 to <%= toInteger %> is: <%= sumOfFirstIntegers %> Listing 4-3 also includes a few JSP expressions. As you may have guessed by now, you can code JSP declarations in XML style syntax as follows: Java Code JSPs also permit you to code pieces of Java in your page by coding scriptlets, as explained in the next section. JSP Scriptlets A scriptlet is an arbitrary piece of Java code. The general format is as follows: <% aPieceOfJavaCode %> Understand that a piece of code can be entire statements or groups of statements. Scriptlets are executed at request time. Hence, code contained in scriptlets may modify objects by invoking methods. Listing 4-4 shows a page similar to Listing 4-3 but using a scriptlet. Listing 4-4: JSP page with a scriptlet <%@ page contentType="text/html" %> <%-- Here's a JSP scriptlet --%> <% int toInteger = 100 ;
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