Transcript Introducing OOP - Northumbria University

Application Integration
JavaServer Pages
Introduction & Overview
 Implicit Objects
 Scripting
 Standard Actions
 Directives
 References

Michael Brockway
Introduction

References: Deitel & Deitel Java chap 25; Liang, Java Programming, chap
40

JavaServer Pages (JSPs) are a way of simplifying the delivery of dynamic
web content


Underneath, they are servlets, but you do not program them in Java;
Rather, you write XHTML documents with embedded






directives
actions
Scriptlets (fragments of Java code)
tag libraries
Accessible to non Java programmers
Even experienced Java programmers are prone to errors when writing a lots of
printlln(...) statements to a reponse object’s printWriter, in order to
create a dynamic web page: it is easier to write the web page and embed the
dynamic bits.
2
Introduction

When a JSP-enabled server receives a request for a JSP





The JSP container (within the server) translates the JSP into a Java servlet
The servlet handles the current and future requests for this JSP
Errors compiling the servlet result in translation-time errors.
JSP container places the Java statements that implement the JSP’s response in
method _jspService at translation time.
If the JSP compiles correctly, the JSP container invokes method _jspService
to process the request.



May respond directly; or
May invoke other Web application components
A first example – clock.jsp

Deploy in Tomcat



...webapps\jspexs\jsp\clock.jsp
jspexs is the context root for the present jsp examples
In web browser, go to

http://localhost:8080/jspexs/jsp/clock.jsp
3
Implicit Objects

A JSP page is XHTML with embedded pieces of Java. These java statements
can refer to a number of implicit objects associated with the page, or the
HTTP request which led to the production of the page, or with the browser
session.

javax.servlet.ServletContext application



javax.servlet.ServletConfig config



Represents the JSP configuration options
Has page scope: exists just in the current page
java.lang.Throwable exception


This object represents the container in which the JSP executes
Scope is “global” – any servlet or JSP in this container can access it
Passed to a JSP error page; has page scope.
javax.servlet.jsp.JspWriter out (page scope)
Writes text in response to a request
 Used implicitly with JSP expressions and actions that output string content
 java.lang.Object page (page scope)
 The this reference

4
Implicit Objects

Implicit objects (ctd)

javax.servlet.jsp.PageContext pageContext (page scope)



Hides implementation of page’s underlying servlet
Provides access to these implicit objects
javax.servlet.http.HttpServletResponse response (page
scope)
 Or some class that implements javax.servlet.ServletResponse
 Implements response to client

javax.servlet.http.HttpServletRequest request




Or some class that implements javax.servlet.ServletRequest
Has request scope: accessible to all pages which are part of this request
Represents the client request
javax.servlet.http.HttpSession session


Represents client session information
Has session scope – the clients entire brwosing session
5
Scripting

You write XHTML with embedded JSP scripting components

Scriptlets




3 kinds of comments




blocks of Java code delimited by <% and %>.
Java expressions delimited by <%= and %>.
Placed in method method _jspService a translation time.
XHTML comments go between <!-- and --!> and can go anywhere in a JSP except
inside scriptlets
JSP comments go between <%-- and --%> and can go anywhere in a JSP except inside
scriptlets; do not appear in response to client
Java comments between /* and */ or between // and end-of-line can go inside
scriptlets
Escape sequences


If you want a literal <%, use escape sequence <\%; for literal %>, use %\>
For literal ', ", \ use escape sequences \', \", \\
6
Scripting

See scripting example welcome.jsp

Deploy in Tomcat


http://localhost:8080/jspexs/jsp/welcome.jsp


…\webapps\jspexs\jsp\welcome.jsp
or
http://localhost:8080/jspexs/jsp/welcome.jsp?firstName=Michael
7
Standard Actions


See examples listed at end of these notes
<jsp:include>


<jsp:forward>



Specifies that the page uses a given JavaBean instance:
Specifies scope of bean
Assigns it an ID that scripting components can refer to
<jsp:setProperty>


Use with the 3 actions above to specify parameters as name,value pairs
<jsp:useBean>




Adds a browser-specific object to a page
<jsp:param


Forwards request to another JSP or servlet or static page.
Terminates current processing
<jsp:plugin>


Dynamically include another referenced resource in a JSP
in a given JavaBean instance
<jsp:getProperty>


in a given JavaBean instance
Converts to String for output to response
8
Directives

Messages to the JSP container allowing programmer to specifiy page settings
Delimited by <%@ and %>
Processed at translation time

include Directive




See example includeDirective.jsp
Guest Book case study





GuestBean.java
GuestDataBean.java
guestBookLogin.jsp
guestBookView.jsp
guestBookErrorPage.jsp
9
Further Reading

WWW Resources

Look at the links from http://java.sun.com/ Java Enterprise Edition
documentation

JavaServer Pages specification
 http://java.sun.com/products/jsp/download.html#specs
Tutorial
 http://java.sun.com/javaee/5/docs/tutorial//doc/
The API referece
 http://java.sun.com/javaee/5/docs/api/
 Look up packages javax.servlet.jsp and javax.servlet.jsp.tagext



The Deitel et al and Liang textbook references cited above.
10