1. COSC 617 Jeff Schmitt September 28, 2006
Ch 4 – JavaServer Pages
COSC 617
Jeff Schmitt
September 28, 2006

2. Servlets Advantages Disadvantages
Servlet mapping (servlet is not a web page)
Hard for Web Designer to change the HTML part of the code
HTML (presentation) and Java code (business logic) mixed together
Scalable
Persistent
Simple
Flexible
Support
Stable API
Run in separate memory space from Server

3. HTML-based interfaces with servlets
Time consuming
Strings of println statements
Configuration files
Changes are error prone
Requires a programmer
Prefer to use a web designer
One approach – use HTML except for forms processing -- limitations

4. Servlet Sequence Diagram
Client
Webserver
Servlet
request()
init()
service()
Process request
response
response
destroy()

5. Servlet Multithreading
Client 1
Servlet
Client 2
request
request
response
response

6. Better approach
Blend dynamic elements directly into the static content
The reverse of the approach servlets use
Use HTML development tool to edit the page (it should ignore the embedded dynamic content tags)
Two approaches
Document templates
JSP

7. Classical Model-View-Controller Architecture
Model Queries
View
Model
Change Notification
User Events
Select a View
Model Changes
Controller
Example: A Clock Application

8. Problems with JSP
Although intended to help separate the presentation logic (VIEW) from the business logic (MODEL), JSP does not go far enough
JSP programs are often a mix of HTML and business logic, which creates a problem if the design of the page (VIEW) needs to be changed
HTML changes need to be made by web designers who are not necessarily programmers
Solutions to this problem include WebMacro, Struts, FreeMarker, Velocity

9. Document templates Template file is HTML with special tags
Template file is run through server-side processor which replaces tags with dynamic content
Example: WebMacro and Velocity
JSP – Sun’s approach
Built on top of Servlet API
Compiled to Servlet
An “Inside-out” servlet

10. FreeMarker Template Processing
Makes substitutions of text in a template based on a set of identifiers in a table ModelRoot)
Works with any form of text files including HTML, XML. and Data files
Template
Cache
ModelRoot
Freemarker
Resulting
web page

11. Freemarker Template Scripting
Value Substitution from rootHash ${request.NAME}
Freemarker Comments <comment> </comment>
List iteration <loop guestbook as entry> </list>
Conditional <if> <else> </if>
Text inclusion from another template file <include "footer.html">

12. FreeMarker Template Cache
Manages the folder where templates are stored
Loads and compiles templates into tokenized form for efficiency
Recognizes changes to templates while application is running

14. JSP -- Java Server Pages
Similar to servlets, but they resemble HTML pages
Placed in web folders mixed with HTML files, acts like an HTML file
Compiled automatically to a servlet when first referenced or when the file is changed by programmer.
Intended to help separate the presentation (HTML response) from the logic (processing logic).
Similar to Microsoft's Application Server Pages (ASP)

15. JSP Lifecycle Client Webserver Servlet JSP request request servlet
JSP to Servlet
Compile Servlet
servlet
service()
init()
Process request
response
response

16. JSP scripting elements
JSP Comments <%-- jsp comment --%>
Declarations: placed in static part of servlet <%! String filePath="/users";%>
Expressions: evaluate to a string <%= request.getParameter("NAME")%>
Scriptlets: any Java statements <% (java statements) %>
Template Text: inserted into response <TABLE BORDER=1> <TR><TH>Name:<TD><INPUT NAME="NAME" size=50 MAXLENGTH=50>

17. JSP Default Objects Object Class Scope Comments request
HttpServletRequest
Request
The client request
response
HttpServletResponse
Page
The servlet response
out
JspWriter
page
An object for writing to the output stream
session
HttpSession
Session
Created to track same user as they visit and return to pages in web application
application
ServletContext
Application
Allows servlets to communicate with each other

18. JSP Object Scope Scope Meaning Page
Available to the handling page only
Request
Available to the handling page and to any servlelt or JSP that control is forwarded to or included
Session
Available to any servlet or JSP within the same session (across repeat visits to web application)
Application
Available to any servlet or JSP within the same web application

19. Custom JSP tags Assemble reusable JSP code for easy use
An XML-like front end to access Java programming
Designed to bridge the intersection between java programmers and web designers
Tag library holds definitions of custom tags taglib uri="jakarta-taglib/dbtags" prefix="sql" %>
Custom tags save in Tag Library File .tld
Many useful Tag Libraries exist for the common tasks such as database access, , file access

20. JSP Action Elements Control Tags for request-time include
Optional parameters for Control tags
Allow JSP programs to implement the Controller aspect of the Model-View-Controller architecture
<jsp:include page="header.jsp"/>
<jsp:forward page="html.jsp/>
<jsp:forward page="html.jsp">
<jsp:param name="page" value="guestview"/>
</jsp:forward>

21. JSP Forward Client Webserver Servlet 1 Servlet 2 JSP request request
JSP to Servlet
Compile Servlet
servlet
service()
Process
request
request
JSP to Servlet
Compile Servlet
servlet
Process
request
service()
response
response

22. date.jsp
<html>
<body>
<%
java.util.Date theDate = new java.util.Date( );
%>
<% if (theDate.getHours( ) < 12) { %>
Good morning,
<% } else { %>
Good afternoon,
<% } %>
visitor. It is now <%= theDate.toString( ) %>
</body>
</html>
Note: <%! For declarations, global to all invocations

23. JSP Page Directive values
autoFlush buffer flushed when full, true
buffer buffer size in kb
contentType default is text/html
errorPage custon error-handling page
import list of java classes/packages
isErrorPage makes exception object available
session page participates in user session

24. Objects avalable in JSP
application ServletContext
config ServletConfig
exception Throwable
out JspWriter
page Object
pageContext PageContext
request HttpServletRequest
response HttoServletResponse
session HttpSession

25. JSP Action Tags
Allow non-programming web designers to develop dynamic content
Action tag looks like regular HTML
Does not follow <% %> syntax
built-in actions
custom tags
include %> directive
(once at compile time)
<jsp:include page=“/header.jsp”/>
(at request time)

26. JavaBean public class Product { private String name = null;
private double price = 0.0d;
public String getName() {
return name; }
public void setName(String name) {
this.name = name;
public double getPrice() {
return price;
public void setPrice(double price) {
this.price = price;
static Product makeProduct(String newName, double newPrice) {
Product p = new Product();
p.setName(newName);
p.setPrice(newPrice);
return p;
JavaBean

27. JavaBeans
<jsp:useBean id=“product” class=“fontanini.ProductBean” scope=“request”/>
<jsp:setProperty name=“product” property=“ProductID” value=“1234”/>
in setProperty, value can be omitted, accesses request value instead
special property name (*) populates every property of the bean from the request parameters

28. JavaBean Scope
<jsp:useBean id=“product” class=“fontanini.ProductBean” scope=“request”/>
page (default)
request
session
application

29. JSP Expression Language
EL for short
JSP engine evaluates the expression and embeds the result in the page

30. product.jsp <%@ taglib uri="http://java.sun.com/jsp/jstl/core"
prefix="c" %>
page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head><title>Product Description</title></head>
<body>
<h1>${product.name}</h1>
Price: $${product.price}
<c:if test="${product.price > 400}">
<br/><font color="red">Eligible for Saver Shipping!</font>
</c:if>
</body>
</html>

31. JSTL Java Standard Tag Library
Easy to incorporate into Web Applications
Necessary jar files go in /WEB-INF/lib
Add to each page:
taglib uri= prefix=“c” %>

32. JSTL variables <%@ taglib uri="http://java.sun.com/jsp/jstl/core"
prefix="c" %>
page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<c:set var="username" scope="session" value="${param.username}"/>
<c:out value="${username}"/>
<c:remove var="username"/>
</html>

33. JSTL Flow Control
page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head><title>Widget Catalog</title></head>
<body>
<ul>
<c:forEach var="product" items="${catalog}">
<li>${product.name}: $${product.price}</li>
</c:forEach>
</ul>
</body>
</html>

34. JSTL I18n JSTL fmt (not core) tag lib External Properties File
message_en.properties
first.name=First Name
last.name=Last Name

35. message.jsp
taglib uri= prefix="fmt" %>
<form>
<fmt:bundle basename="messages">
<table>
<tr><td>
<fmt:message key="first.name"/>
</td><td><input type="text" name="firstname"></td></tr>
<fmt:message key="last.name"/>
</td><td><input type="text" name="lastname"></td></tr>
</table>
</fmt:bundle>
<input type="submit" value="Submit">
</form>

36. Wrapping Up
Questions?