Java Server Pages

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Java Server Pages

• Russell Beale

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What are Java Server Pages?

• Separates content from presentation
• Good to use when lots of HTML to be presented to
  user, with small amounts of processing
• Uses java
• But is a bit like asp, php, perl etc.
• Page compiled to a servlet when first executed

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Uses

• Often jsp pages used to present the information
  to the user
• Developers code the servlets, called from the jsp
  page
• Designers code the HTML to pull all these
  different components together

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JSP pages

• Text file containing HTML (or XML) along with JSP
  elements, which are shorthand for java code
• The JSP parts provide the dynamic content
• In tags
• lt gt
• Give file a .jsp extension, (typically) put it
  wherever you would a web page

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JSP page constructs

• HTML
• Most of the page - known as template text
• Scripting elements
• Specify Java code that becomes part of the
  servlet
• Directives
• Control overall structure of servlet
• Actions
• Specify existing components that should be used

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Scripting elements

• lt
• java code
• gt
• Any amount of java code
• Variables available
• request (subclass of HttpServletRequest)
• response (subclass of HttpServletResponse)
• session
• out
• Known as scriplets as well

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E.g.

• lt
• String userNamenull
• userNamerequest.getParameter(userName)
• gt

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Expression

• lt expression gt
• Expression is evaluated and placed in output
• E.g.
• lt request.getParameter(title) gt
• Puts the value of title into the output

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Directives

• affects the overall structure of the servlet
  class
• lt_at_ directive attribute"value" gt
• two main types of directive
• page, which lets you do things like import
  classes, customize the servlet superclass, etc.
• include, which lets you insert a file into the
  servlet class at the time the JSP file is
  translated into a servlet.

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Declaration

• lets you define methods or fields that get
  inserted into the main body of the servlet class
  (outside of the service method processing the
  request).
• lt! Java Code gt
• declarations do not generate any output -
  normally used in conjunction with JSP expressions
  or scriptlets.

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Actions

• Control behaviour of servlet engine

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Bigger e.g.

• See index

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Summary

• JSP good for
• Quick and dirty dynamic pages
• Pages with lots of html and less code
• Separation of presentation from content
• JSP pages are converted into servlets for you