JSP Application Design

1
JSP Application Design

• CC292
• Simon M. Lucas

2
Main Features of JSP

• Get / Set properties
• Via getX setX naming patterns
• Has the advantage of auto-capturing form data
• Also
• Other data fields on a Java Object can be set
• And then those values used in other pages
• Convenient for page inclusion and forwarding

3
Model View Controller (MVC)

• The MVC architecture is one way to approach web
  application design
• This uses a controller page to handle all
  requests
• The controller reads any query or form parameters
• Decides on which action to take
• Then dispatches control to another page to take
  the action

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MVC Architecture
Request Proc.jsp?pageAccountidsml
Proc.jsp
Action1.jsp
Account.jsp
Checkout.jsp
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MVC Continued

• Often implemented with Java Servlets
• But can be done just as easily with JSP
• And Java support classes where needed
• In previous example
• Proc.jsp would extract the Account info for the
  given id
• Then pass control to the Account.jsp page
• Having set up the appropriate values (perhaps as
  Beans)

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Forward and Include

• Two ways to pass control to another JSP page
• ltjspforward pageAccount.jspgt
• Terminates execution of current page
• Transfers control to the forwardee
• ltjspinclude pageAccount.jspgt
• Executes the specified page
• Then returns control to the current page

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JSP Include Example

• JSP include very widely used
• Include dynamic data components in a calling page
  see below

Banner
Index
Basket
Products
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Taking Care with Beans

• To be passed from caller to callee, use the
  appropriate scope
• Usually, request
• Page would be restricted to the calling page and
  would not work.
• Scope must be the same for caller and callee!
• Be careful about using Application or Session
  scope why?

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Explanation

• idtable this sets up a variable name that
  can be used later on the same page, and
  referenced with ltuseBeangt on other pages
• classtable.Table the bean will be
  instantiated to be an object of this Class
• scoperequest want it to be passed from
  caller to callee

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Table Example Caller

• ltjspuseBean id"table" class"table.Table"
  scope"request"/gt
• lthtmlgt
• ltheadgtlttitlegtSimple JSP page to test a Generic
  Tablelt/titlegtlt/headgt
• ltbodygt
• lth2gtIncluded Table Testlt/h2gt
• lt // note cannot use table new ... here -
• // would not get passed to the included
  page
• // but table.table new ... is fine
• table.table new
• StudentTable(ReadStudents.readStudents(
• "c/tomcat5/webapps/test/data/students.t
  xt")) gt
• ltjspinclude page"Table.jsp" /gt

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Table Example Callee (Table.jsp)

• ltjspuseBean id"table" class"table.Table"
  scope"request"/gt
• lttablegt
• lt--
• First do the table head, then all the rows
• --gt
• lttrgt
• lt
• for (Object data table.table.getHead
  er().getData())
• gt
• ltthgtlt data gtlt/thgt
• lt
• gt
• lt/trgt
• ... // continued for rows

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Table.jsp (continued now the rows)

• lt
• for (Row row table.table.getRows()) gt
  lttrgtlt
• for (Object data row.getData())
• gt lttdgtlt data gtlt/tdgt lt
• gtlt/trgt lt
• gt
• lt/tablegt

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Sample Output(CSS used but not in these slides)
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But Required Some Java behind the Scenes

• Table.java
• package table
• public class Table
• // use a concrete class to pass the data
  interface
• public Tabular table

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Tabular Interface

• Can be implemented by various concrete classes to
  deliver data from data sources
• package table
• import java.util.ArrayList
• public interface Tabular
• public Row getHeader()
• public ArrayListltRowgt getRows()

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Row Interface

• Study this code this is the end of the object
  model data cells simply returned as Strings
• package table
• import java.util.ArrayList
• public interface Row
• ArrayListltStringgt getData()

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Summary

• Key JSP concepts
• Forward and Include
• Beans and Bean Scope
• Study Table example
• Worked with request scope
• Question What are the advantages and
  disadvantages of generic tables versus writing a
  specific JSP page for each table?