EBIZ 5535 Lecture 4

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EBIZ 5535Lecture 4

• JSP Directives and Actions

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Outline

• JSP Directives
• Page directive
• Include directive
• JSP Actions
• jspinclude
• jspuseBean
• jspsetProperty
• jspgetProperty
• jspforward

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JSP Directives

• A JSP directive affects the overall structure of
  the servlet class
• lt_at_ directive attribute"value" gt
• Or
• lt_at_ directive attribute1"value1"
• attribute2"value2"
• ...
• attributeN"valueN" gt

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Types of Directives

• There are two main types of directive
• page, which lets you do things like import
  classes, customize the servlet superclass
• 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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The JSP page Directive

• Lets you define one or more of the following
  case-sensitive attributes
• import"package.class" or import"package.class1,.
  ..,package.classN".
• Examplelt_at_ page import"java.util." gtThe
  import attribute is the only one that is allowed
  to appear multiple times.
• contentType"MIME-Type" or contentType"MIME-Type
  charsetCharacter-Set"Examplelt_at_ page
  contentType"text/plain" gt

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More Page Attributes

• errorPage"url". This specifies a JSP page that
  should process any Throwables thrown but not
  caught in the current page.
• isErrorPage"truefalse". This indicates whether
  or not the current page can act as the error page
  for another JSP page. The default is false.
• isThreadSafe"truefalse"
• session"truefalse"
• buffer"sizekbnone" This specifies the buffer
  size for out. The default is server-specific, but
  must be at least 8kb

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More Page Attributes

• autoflush"truefalse". A value of true, the
  default, indicates that the buffer should be
  flushed when it is full.
• extends"package.class". This indicates the
  superclass of servlet that will be generated. Use
  this with extreme caution, since the server may
  be using a custom superclass already.
• info"message". This defines a string that can be
  retrieved via the getServletInfo method

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The JSP include Directive

• Lets you include files at the time the JSP page
  is translated into a servlet
• lt_at_ include file"relative url" gt
• Interpreted as a JSP.
• You can tell the system to interpret the URL
  relative to the home directory of the Web server
  by starting the URL with a forward slash.

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Example of Using Include

• lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
  Transitional//EN"gt
• ltHTMLgt
• ltHEADgt
• ltTITLEgtJavaServer Pages (JSP) 1.0lt/TITLEgt
• lt/HEADgt
• ltBODYgt
• lt_at_ include file"/navbar.html" gt
• lt!-- Part specific to this page ... --gt
• lt/BODYgt
• lt/HTMLgt

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Example

• JspTest.jsp

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JSP Actions

• JSP actions use constructs in XML syntax to
  control the behavior of the servlet engine.
• jspinclude - Include a file at the time the page
  is requested
• jspuseBean - Find or instantiate a JavaBean
• jspsetProperty - Set the property of a JavaBean
• jspgetProperty - Insert the property of a
  JavaBean into the output
• jspforward - Forward the requester to a new page
• jspplugin - Generate browser-specific code that
  makes an OBJECT or EMBED tag for the Java plugin

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The jspinclude Action

• This action lets you insert files into the page
  being generated
• ltjspinclude page"relative URL" flush"true" /gt
• Unlike the include directive, this action inserts
  the file at the time the page is requested
• Precludes the included page from containing
  general JSP code (it cannot set HTTP headers, for
  example), but it gains significantly in
  flexibility

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Example

• lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
  Transitional//EN"gt
• ltHTMLgt ltHEADgt
• ltTITLEgtWhat's Newlt/TITLEgt
• lt/HEADgt
• ltBODY BGCOLOR"FDF5E6" TEXT"000000
• LINK"0000EE" VLINK"551A8B" ALINK"FF0000"gt
• ltCENTERgt
• ltTABLE BORDER5 BGCOLOR"EF8429"gt ltTRgtltTH
  CLASS"TITLE"gt What's New at JspNews.comlt/TABLEgt
• lt/CENTERgt
• ltPgt Here is a summary of our four most recent
  news stories ltOLgt ltLIgtltjspinclude
  page"news/Item1.html" flush"true"/gt
  ltLIgtltjspinclude page"news/Item2.html"
  flush"true"/gt ltLIgtltjspinclude
  page"news/Item3.html" flush"true"/gt
  ltLIgtltjspinclude page"news/Item4.html"
  flush"true"/gt lt/OLgt
• lt/BODYgt lt/HTMLgt

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The jspuseBean Action

• This action lets you load in a instance to be
  used in the JSP page
• Useful because it lets you exploit the
  reusability of Java classes without sacrificing
  the convenience that JSP adds
• ltjspuseBean id"name" class"package.class" /gt
• Usually, instantiate an object (called a bean) of
  the class specified by class and bind it to
  variable name

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jspgetProperty/setProperty

• Once you have a bean, you can modify its
  properties via jspsetProperty, or by using a
  scriptlet
• With beans, "this bean has a property of typeX
  called foo", really means "this class has a
  method called getFoo that returns something of
  type X, and another method called setFoo that
  takes an X as an argument

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Example

• lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0
  Transitional//EN"gt
• ltHTMLgt ltHEADgt
• ltTITLEgtReusing JavaBeans in JSPlt/TITLEgt
• lt/HEADgt
• ltBODYgt ltCENTERgt
• ltTABLE BORDER5gt ltTRgt
• ltTH CLASS"TITLE"gt Reusing JavaBeans in
  JSPlt/TABLEgt
• lt/CENTERgt
• ltPgt ltjspuseBean id"test" class"SimpleBean" /gt
• ltjspsetProperty name"test" property"message"
  value"Hello WWW" /gt
• ltH1gtMessage ltIgt ltjspgetProperty name"test"
  property"message" /gt lt/Igtlt/H1gt lt/BODYgt lt/HTMLgt

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Example contd

• public class SimpleBean
• private String message "No message
  specified"
• public String getMessage() return(message)
  
• public void setMessage(String message)
  this.message message
• Note Install beans in the servlet directory

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Equivalent to Scriptlets

• ltjspuseBean id"test" class"SimpleBean" /gt
• Equivalent scriptlet
• lt SimpleBean test new SimpleBean() gt
• ltjspsetProperty name"test" property"message"
  value"Hello WWW" /gt
• Equivalent scriptlet
• lt test.setMessage(Hello WWW) gt

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Equivalent Scriptlets contd

• ltjspgetProperty name"test" property"message"
  /gt
• Equivalent scriptlet
• lt test.getMessage() gt

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Setting Bean Properties to JSP Page Parameters

• Typically, one wants to use a bean to process the
  parameters sent to a JSP page.
• jspsetProperty is set up to pass parameters to a
  bean very easily
• What we want is something like this on our JSP
  page
• ltjspsetProperty nametest propertymessage
• value lttest.getParam(message) gt

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• http//www.myserver.edumyport/mypage.jsp?message
  hithere
• When this page is accessed, the setMessage method
  of the bean is called with argument hi there

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Conversion of Non-String Parameters

• All parameters have string values, but these
  values are converted when bean properties have
  other types
• lt int numItems 1
• try
• numItems Integer.parseInt
• (request.getParameter
• (numItems))
• catch (NumberFormatException e)
• gt

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• ltjspsetProperty name entry
• propertynumItems
• value ltrequest.getProperty(numItems) gt
• /gt
• Equivalent to
• ltjspsetProperty name entry
• propertynumItems
• paramnumItems /gt

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So

• Use the param attribute of setProperty to
  indicate that
• Value should come from specified request
  parameter
• Simple automatic type conversion should be
  performed

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Associating All Properties with Input Parameters

• Use for the value of the property attribute
  of jspproperty to indicate that
• Value should come from request parameter whose
  name matches property name
• Simple automatic type conversion should be
  performed
• ltjspsetProperty nametest
• property /gt