Transcript Chapter 11 - SaigonTech

Chapter 11
Invoking Java Code with JSP
Scripting Elements
Contents
1.
2.
3.
4.
5.
6.
7.
Creating Template Text
Invoking Java Code from JSP
Using JSP Expressions
Example: JSP Expressions
Writing Scriptlets
Scriptlet Example
Using Scriptlets to Make Parts of the JSP Page
Conditional
8. Using Declarations
9. Declaration Example
10. Using Predefined Variables
1. Creating Template Text

A large percentage of your JSP document consists of
static text
HTML looks just like normal HTML
Using tools to build the Web pages
“template text is passed straight through”
You need to put <\% or %\> in the template text
<%-- JSP Comment --%>
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<!-- HTML Comment -->
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2. Invoking Java Code from JSP
2. Invoking Java Code from JSP
(Cont.)
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Expressions of the form <%= Java Expression %>
Scriptlets of the form <% Java Code %>
Declarations of the form <%! Field/Method
Declaration %>
3. Using JSP Expressions
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<%= Java Expression %>
Current time: <%= new java.util.Date() %>
Predefined Variables
• request, the HttpServletRequest
• response, the HttpServletResponse
• session, the HttpSession associated with the
request
• out, the Writer (a buffered version of type
JspWriter)
• application, the ServletContext
 Tomcat Autogenerated Servlet Source Code:
install_dir/work/Standalone/localhost/_
4. Example: JSP Expressions
5. Writing Scriptlets
complex than output the value of a simple expression
<% Java Code %>
 explicitly send output to the resultant page
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<%
String queryData = request.getQueryString();
out.println("Attached GET data: " + queryData);
%>
<% String queryData = request.getQueryString(); %>
Attached GET data: <%= queryData %>
Attached GET data: <%= request.getQueryString() %>
5. Writing Scriptlets (Cont.)
6. Scriptlet Example

JSP page that uses the
bgColor request parameter
to set the background color
of the page
7. Using Scriptlets to Make Parts of
the JSP Page Conditional
7. Using Scriptlets to Make Parts of
the JSP Page Conditional (Cont.)
8. Using Declarations
Define methods or fields
<%! Field or Method Definition %>
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Define most methods with separate Java classes, not
JSP declarations.
8. Using Declarations (Cont.)
9. Declaration Example
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prints the number of times the current page has been
requested since the server was booted
<%! private int accessCount = 0; %>
Accesses to page since server reboot: <%= ++accessCount %>
10. Using Predefined Variables
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1.
2.
3.
4.
5.
6.
Variable names the autogenerated servlet uses
request is the HttpServletRequest associated with
the request
response is the HttpServletResponse associated
with the response to the client
out is the writer used to send output to the client
Session is the HttpSession object associated with
the request
application is the ServletContext as obtained by
getServletContext
config is the ServletConfig object for this page
10. Using Predefined Variables
(Cont.)
7. pageContext give a single point of access to many of
the page attributes.
8. page is simply a synonym for this and is not very
useful
Q & A?

Thank you!