Java Server Pages

1
Java Server Pages

• An introduction to JSP

2
Containers and Components

• Several clients one system

3
Java Server Pages (JSP)

• HTML with embedded Java code
• Good for presentation
• No print statements
• Compiled to a Servlet at runtime
• Good performance
• Easy deployment
• When a JSP is updated its recompiled
• Possible to compile manually
• Easy for web designers to use
• Edited in an ordinary HTML editor
• Support for Java Beans and Custom tags

4
JSP Directives

• At the top of a JSP page, the page directive is
  used
• lt_at_ page namevalue gt

5
JSP Page Directive parameters

• language
• Default is java
• extends
• Default is the base JSP class, but you could use
  your own
• importpackage1,package2, class1, class2
• session
• True or False, determines if sessions should be
  automatically created. True is default

6
JSP Page Directive parameters

• buffer
• The output buffer size
• autoFlush
• True or false, determines if the output should be
  flushed to the client. True is default
• isThreadSafe
• True or false. True is default
• info
• Descriptive text

7
JSP Page Directive parameters

• errorPage
• The page to go to in case of an error
• contentType
• isErrorPage
• Defines if this is a error page. False is
  default. If its an error page a couple of extra
  objects are available in the page

8
Other Directives

• Include directive
• lt_at_ include filerelative url gt
• Includes the file BEFORE compilation
• Only static content

9
JSP Implicit objects

• In JSPs, a couple of objects are allways
  available
• request
• Subclass of ServletRequest
• getParameter(), getParameterNames()
• getAttribute()
• Response
• Subclass of ServletResponse
• Not used in normal situations
• pageContext
• Used to get configuration variables for this page
• getAttribute()

10
JSP Implicit objects

• session
• The HttpSession
• Created automatically if session is not false in
  the page directive
• application
• javax.servlet.ServletContext
• Used to get information about the application
• out
• Used to print (in scriptlets)
• clear(), clearBuffer(), flush()
• config
• javax.servlet.ServletConfig
• getInitParameter(), getInitParameterNames()
• page
• exception

11
JSP Implicit objects

• exception
• Only in error pages
• getMessage()
• printStackTrace()

12
Java Code

• Three ways to use Java Code in your JSP
• lt! Declaration gt
• Declares member variables
• NOT thread safe
• lt MyClass.printMessage() gt
• Used to print single expressions

13
Java Code

• lt any java code gt
• Can contain the entire application
• Use with care
• Can give very hard to read code
• lt if(status 1)
• gt
• lth3gtYolt/h3gt
• lt
• Else
• gt
• lth3gtOylt/h3gt
• lt gt

14
JSP Tags

• There are a couple of tags available and you can
  extend the tag set with your own tags
• XML Syntax
• Doesnt distract HTML authoring tools

15
Forward

• ltjspforward pagerelative URL /gt
• Forwards the request

16
Include

• ltjspinclude pagerelative url
  flusthtrue/false /gt
• Includes the output in runtime
• Can be dynamic content

17
UseBean

• ltjspuseBean idinstance name
  scopepagerequestsessionapplication
  beanNamepackage.classclasspackage.class /gt
• Used to initialize a bean. Only called once
• ltjspuseBean gt
• lth4gtThe bean is createdlt/h4gt
• lt/jspuseBeangt

18
GetProperty

• Used to call getXXX methods in a bean
• ltjspgetProperty namebean instance name
  propertyname /gt
• Will call bean.getName()
• Name is the same as id in ltjspuseBeangt

19
SetProperty

• Used to call setXXX methods in a bean
• ltjspsetProperty nameinstance name
  propertypropertyname valuevalue /gt
• When is used as property name, a setXXX for
  value in getParameterNames() will be called

20
Example

• package test1
• class TestBean
• private String name
• private String surname
• public String getName()
• return name
• public String getSurname()
• return surname
• public void setSurname(String _surname)
• surname_surname
• public void setName(String name_name)
• name_name

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Example cont.

• lt_at_ page langueajava sessiontrue gt
• ltjspuseBean idtb classtest1.TestBean
  scopesessiongt
• ltigtThe bean is created lt/igt
• ltjspgetProperty nametb propertyname /gt
• ltjspsetProperty nametb propertyname
  valueFredrik /gt