This document discusses JavaBeans and the Expression Language (EL) in Java Server Pages (JSP). It describes how JavaBeans are reusable Java components that follow conventions for properties and methods. The EL allows easier access to JavaBeans properties without scripting code. It provides implicit objects to access attributes, request parameters, cookies and context initialization parameters. The EL supports operators and functions for conditions and evaluations.

1. Chapter 8
Script-free Pages
St.Actions and EL

2. MVC model: set/get attributes
As
strings
Value of the “name” attribute

3. javaBeans (not EJB)
• reusable software components
• classes written in Java conforming to a particular convention
• used to encapsulate many objects into a single object (the
bean), so that they can be passed around as a single bean
object
• a Java Object that
• is serializable,
• has a nullary constructor, and
• allows access to properties using getter and setter methods.

4. MVC model: set/get attributes
As
instance
s

5. JavaBean standard actions
Print the result of getName()
Using an expression this is a javaBean

6. <jsp:useBean> and <jsp:getProperty>
Standard action
Identifier of bean object
Class type

7. <jsp:useBean> to create a bean
_jspService()

8. <jsp:setProperty>

9. Conditional body in <jsp:useBean>

10. class = reference = object type
Polymorphic (reference and object) bean references

11. Reference ≠ object type?
Abstract class
Concrete class
in package foo

12. add a type attribute to the tag

13. No class just type

14. Add a scope attribute
default

15. From the request to the JSP. Directly!

16. Add a param attribute
Set bean
property to
value of the
request
parameter

17. All request parameters match bean properties

18. person has a dog & dog has a name

19. property of a property?

20. Expression Language (EL)

21. Expression Language (EL)
A scripting language which allows easier
access to JavaBeans through JSP.
Access Java objects without using Java
Widely spread

22. Moving towards the designer

23. The EL language
Map objects

24. “[]” instead of “.”
An index
into a list
of arrays

25. example
Beware: [] does not mean “array”

26. Example
(use either
“.” and “[]”)
example
(beans and maps)

27. Deeper understanding

28. Nesting

29. Back to EL implicit
objects
M
aps
to
scope
attributes
M
aps
to
requestparam
s
M
ap
ofcookies
M
aps
to
requestheaders
M
ap
ofcontextinnate
param
s
reference
to
object

30. Requesting
Parameters

31. Getting useful staff
• Scripting
• Host is: <%= request.getHeader(“host”) %>
• Method is: <%= request.getMethod() %>
• EL
• Host is: ${header[“host”]}
• Host is: ${header.host}
• Method is: ${request.method}
• Method is: ${requestScope.method}
• Method is: ${pageContext.request.method}
Gives attributes
(not properties)
There is
no such
implicit
object

32. Prefacing attributes
• Control scoping
${person.name} or ${requestScope.person.name}
• Avoid problems with the name’s string nature
request.setAttribute(“person”, p);
request.setAttribute(“foo.person”, p);
${foo.person.name}
${requestScope[“foo.person”].name}

33. Cookies & init
params
<% Cookie[] cookies = request.getCookies();
for (int i = 0; i < cookies.length; i++)
{ if ((cookies[i].getName()).equals(“userName”)) {
out.println(cookies[i].getValue());
}
} %>
${ cookie.userName.value}
<context-param>
<param-name>mainEmail</param-name>
<param-value>likewecare@wickedlysmart.com </param-value>
</context-param>
email is: <%= application.getInitParameter(“mainEmail”) %>
email is: ${ initParam.mainEmail}

34. EL functions

35. EL operators
<c:if test="${sessionScope.cart.numberOfItems > 0}">
...
</c:if>
<c:if test="${bean1.a < 3}" >
...
</c:if>
<c:if test="true" >
...
</c:if>
<mytags:example attr1="an expression is ${'${'}true}" />