JSP

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JSP

• Java Server Pages

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Java Server Pages

• JSP (Java Server Pages) is an alternate way of
  creating servlets
• JSP is written as ordinary HTML, with a little
  Java mixed in
• The Java is enclosed in special tags, such as lt
  ... gt
• The HTML is known as the template text
• JSP files must have the extension .jsp
• JSP is translated into a Java servlet, which is
  then compiled
• Servlets are run in the usual way
• The browser or other client sees only the
  resultant HTML, as usual
• Tomcat knows how to handle servlets and JSP pages

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Jsp Execution
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JSP scripting elements

• There is more than one type of JSP tag,
  depending on what you want done with the Java
• lt expression gt
• The expression is evaluated and the result is
  inserted into the HTML page
• lt code gt
• The code is inserted into the servlet's service
  method
• This construction is called a scriptlet
• lt! declarations gt
• The declarations are inserted into the servlet
  class, not into a method

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Example JSP

• ltHTMLgtltBODYgtHello!  The time is now lt new
  java.util.Date() gtlt/BODYgtlt/HTMLgt

• Notes
• The lt ... gt tag is used, because we are
  computing a value and inserting it into the HTML
• The fully qualified name (java.util.Date) is
  used, instead of the short name (Date), because
  we havent yet talked about how to do import
  declarations

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Variables

• You can declare your own variables, as usual
• JSP provides several predefined variables
• request The HttpServletRequest parameter
• response The HttpServletResponse parameter
• session The HttpSession associated with the
  request, or null if there is none
• out A JspWriter (like a PrintWriter) used to
  send output to the client
• Example
• Your hostname lt request.getRemoteHost() gt

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Scriptlets

• Scriptlets are enclosed in lt ... gt tags
• Scriptlets do not produce a value that is
  inserted directly into the HTML (as is done with
  lt ... gt)
• Scriptlets are Java code that may write into the
  HTML
• Examplelt String queryData request.getQueryStr
  ing() out.println("Attached GET data "
  queryData) gt
• Scriptlets are inserted into the servlet exactly
  as written, and are not compiled until the entire
  servlet is compiled
• Examplelt if (Math.random() lt 0.5) gt
  Have a ltBgtnicelt/Bgt day!lt else gt
  Have a ltBgtlousylt/Bgt day!lt gt

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Declarations

• Use lt! ... gt for declarations to be added to
  your servlet class, not to any particular method
• Caution Servlets are multithreaded, so nonlocal
  variables must be handled with extreme care
• If declared with lt ... gt, variables are local
  and OK
• Data can also safely be put in the request or
  session objects
• Examplelt! private int accessCount 0 gt
  Accesses to page since server reboot lt
  accessCount gt
• You can use lt! ... gt to declare methods as
  easily as to declare variables

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Directives

• Directives affect the servlet class itself
• A directive has the form lt_at_ directive
  attribute"value" gtor lt_at_ directive
  attribute1"value1"
  attribute2"value2"
  ... attributeN"valueN"
  gt
• The most useful directive is page, which lets you
  import packages
• Example lt_at_ page import"java.util." gt

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JSP Comments

• Different from HTML comments.
• HTML comments are visible to client.
• lt!-- an HTML comment --gt
• JSP comments are used for documenting JSP code .
• JSP comments are not visible client-side.
• lt-- a JSP comment --gt

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The include directive

• The include directive inserts another file into
  the file being parsed
• The included file is treated as just more JSP,
  hence it can include static HTML, scripting
  elements, actions, and directives
• Syntax lt_at_ include file"URL " gt
• The URL is treated as relative to the JSP page
• If the URL begins with a slash, it is treated as
  relative to the home directory of the Web server
• The include directive is especially useful for
  inserting things like navigation bars

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Actions

• Actions are XML-syntax tags used to control the
  servlet engine
• ltjspinclude page"URL " /gt
• Inserts the indicated relative URL at execution
  time (not at compile time, like the include
  directive does)
• This is great for rapidly changing data
• ltjspforward page"URL" /gtltjspforward page"lt
  JavaExpression gt" /gt
• Jump to the (static) URL or the (dynamically
  computed) JavaExpression resulting in a URL

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JSP in XML

• JSP can be embedded in XML as well as in HTML
• Due to XMLs syntax rules, the tags must be
  different (but they do the same things)
• HTML lt expression gtXML ltjspexpressiongtexpre
  ssionlt/jspexpressiongt
• HTML lt code gtXML ltjspscriptletgtcodelt/jspscr
  iptletgt
• HTML lt! declarations gtXML ltjspdeclarationgtde
  clarationslt/jspdeclarationgt
• HTML lt_at_ include fileURL gtXML
  ltjspdirective.include file"URL"/gt

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Action useBean tag

• The useBean action tag is the most commonly used
  tag because of its powerful features.
• It allows a JSP to create an instance or receive
  an instance of a Java Bean.
• It is used for creating or instantiating a bean
  with a specific name and scope.
• Examples
• ltjspuseBean idtime" scope"session"
  class"com.time.CurrentTimeBean" /gt

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Session in jsp

• In session management whenever a request comes
  for any resource, a unique token is generated by
  the server and transmitted to the client by the
  response object and stored on the client machine
  as a cookie.
• Session management
• (i) Session Object
• (ii) Cookies
• (iii) Hidden Form Fields
• (iv) URL Rewriting

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Javascript
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JavaScript language

• The JavaScript language is an interpreted, object
  oriented based scripting language.
• JavaScript coding statements are commonly
  embedded inside a webpage using the HTML tags
  ltSCRIPTgt lt/SCRIPTgt.
• When the web browser is rendering the webpage,
  any JavaScript coding statements encountered are
  immediately interpreted and run before the
  rendering continues.

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Where to use JavaScript

• Verify the end user input data contains
  legitimate data values.
• Handle any arithmetic or logic processing that
  needs to be executed on the web browser.
• Directly manipulate the web browser objects such
  as the status bar, address bar, and the web
  browser's rendered controls (such as textboxes,
  selection lists, etc...).
• Handle and process client-side events that have
  been generated.

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How to run JavaScripts

• JavaScript statements are interpreted and run by
  the web browser
• Most common web browsers contain a JavaScript
  interpreter program
• interpret and run the JavaScript commands that
  have been embedded inside a webpage. 
• Question1 In a web application, which entity
  executes JSPs?
• Question2 In a web application, which entity
  executes JavaScript commands?

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JavaScript programming example

• ltHTMLgt
• 2 ltHEADgtltTITLEgt JavaScript Example1
  lt/TITLEgtlt/HEADgt
• 3 ltBODYgt
• 4 ltH1gtJavascript Example1lt/H1gt
• 5 An alert box will appear using the window
  object ltbrgt
• 6
• 7 ltSCRIPTgt
• 8 window.alert("hello world")
• 9 lt/SCRIPTgt
• 10
• 11 Goodbye!
• 12
• 13 lt/BODYgt
• 14 lt/HTMLgt

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Events

• An event is an identifiable occurrence or action
  that has taken place in the system. Writing
  programs that generate and handle events is known
  as event programming.
• Events are typically generated in the following
  ways.
• GUI programs can generate an event to indicate
  there has been some interaction between the
  widget and the end user.
• when an end user presses a button, a click event
  is generated.
• Input/output programs can generate an event to
  indicate an input/output event has occurred.
• A mouse event is generated when the end user
  moves the mouse.

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Binding Events
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Binding Events

• In client side web programming, the web browser
  contains
• it's own event listener.
• Therefore you must do two things
• in order to process an event that has been
  generated.
• 1. Write the code that binds the event to the
  event handler.
• 2.  Write the code for the event handler.

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Common web browser events