MIS 415 Module 3 3Tier Webapps using JSPJDBC

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MIS 415 Module 33-Tier Webapps using JSP/JDBC

• Arijit Sengupta

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Structure of this semester
MIS415
1. Design
4. Advanced Topics
2. Querying
0. Intro
3. Applications
Database Fundamentals
Conceptual Modeling
Query Languages
Java DB Applications JDBC/JSP
XML Databases
Relational Model
Advanced SQL
Data Mining
Normalization
Newbie
Users
Professionals
Designers
Developers
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Todays Buzzwords

• 3-Tier applications
• Client WebServer ApplicationServer
• Basics of JDBC
• Basics of JSP Containers - Tomcat
• Web Applications using JSP

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JDBC

• A platform-independent library of classes
  allowing database access from any Java
  application
• Take advantages of Polymorphism
• JDBC is a set of interfaces
• Driver, Connection, Statement, ResultSet, etc.
• Database vendors (not programmers) will implement
  these interfaces.
• If we switch from one database to another, we
  just need to load different driver (plug and
  play)!
• YOU DON'T NEED TO MODIFY THE REST OF YOUR PROGRAM!

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JDBC
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JDBC
DriverManager
Connection
Statement
ResultSet
Driver
Database
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JDBC (Contd.)

• Register a JDBC driver
• Driver d new oracle.jdbc.driver.OracleDriver()
• DriverManager.registerDriver (d)
• or
• DriverManager.registerDriver (new
  oracle.jdbc.driver.OracleDriver())
• Or, use the Java reflection abilities
• Class.forName(
• "oracle.jdbc.driver.OracleDriver")
• calling Class.forName() will create an instance
  of a driver and register it with the
  DriverManager automatically
• This is better since we can use a constant
• String DRIVER "oracle.jdbc.driver.OracleDriver"
  
• Class.forName(DRIVER)

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JDBC
DriverManager
Connection
Statement
ResultSet
Driver
Database
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JDBC (Contd.)

• Make a connection
• String URL "jdbcoraclethin_at_unixapps1.wright.e
  du1521ORA2"
• Connection conn
• DriverManager.getConnection(URL, USERNAME,
  PASSWORD)

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JDBC
DriverManager
Connection
Statement
ResultSet
Driver
Database
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JDBC (Contd.)

• Create a statement
• Statement st conn.createStatement()
• //defaultTYPE_FORWARD_ONLY and CONCUR_READ_ONLY
• or
• Statement st conn.createStatement(
• ResultSet.TYPE_SCROLL_SENSITIVE,
  
• ResultSet.CONCUR_UPDATABLE)
• //the resultset will be scrollable and sensitive
  to changes made by others
• //we can update the resultset

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JDBC
DriverManager
Connection
Statement
ResultSet
Driver
Database
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JDBC (Contd.)

• Execute a query
• String SQL "INSERT INTO s"
• " VALUES ('222-22-2222')"
• int result st.executeUpdate(SQL)
• //either the row count for INSERT, UPDATE or
  DELETE or 0 for SQL statements that return
  nothing
• Execute a query and create a resultset
• String SQL "SELECT FROM Student"
• ResultSet rec st.executeQuery(SQL)

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JDBC (Contd.)

• Process the resultset
• while(rec.next()) System.out.println(rec.getStri
  ng("snum"))
• or
• while(rec.next()) System.out.println(rec.getStri
  ng(1))
• // first column of the resultset
• There are methods like getString(), getInt(),
  etc. that take either a column name or column
  position
• See http//java.sun.com/j2se/1.3/docs/guide/jdbc/i
  ndex.html for all JDBC Class documentation

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Tomcat a J2EE Container

• Open Source integrated as an Apache.org project
• Can be obtained from http//tomcat.apache.org
• Provides full JSP 2.0/Servlet 2.4 functionality
• I have created one container environment for each
  team

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Logging in

• Log into my server busdb2.wright.edu using any
  ssh client (putty/ssh.com/)
• Start your server
• From the home directory, type
• webstart
• Stop your server
• webstop
• Test your server
• http//busdb2.wright.edultyourportgt/
• http//busdb2.wright.edultyourportgt/numguess.jsp
• Your jsp files go under
• tomcat/webapps/ROOT
• Your class files go under
• Tomcat/webapps/ROOT/WEB-INF/classes/ltyourpackagegt

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Elements of a Java Server Page

• Directives lt_at_ gt
• Provide global information to the page
• Import statements
• Scripting language
• u Declarations lt! gt
• For page-wide variable and method declarations

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Elements of a Java Server Page

• Scriptlets lt gt
• This is the Java code embedded in the web pages
• Expressions lt gt
• Formats the expression as a string to be included
  in the output of the web page
• Comments lt-- --gt
• User readable comments, contents ignored and
  removed by the JSP Compiler

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JSP Directives

• General syntax
• lt_at_ directive attribute "value" gt
• Possible values for directives are
• Page - Information for the page
• Include - Specifies the files whose contents are
  to be included in the output
• e.g., lt_at_ include file"header.html" gt
• Taglib
• The URI for a library of custom tags that may be
  used in the page

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JSP Page Directive

• The page directive may take the following values
• lt_at_ page language "java" gt
• This variable tells the JSP engine what language
  will be used in the file
• "java" is the only language supported by JSP in
  the current specification
• lt_at_ page import "java.util., ItemValue" gt
• Comma separated list of classes and packages that
  are used in the JSP page
• Should appear at the top of the file

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JSP Page Directive (Contd.)

• lt_at_ page session "true false" gt
• true indicates that session data is available to
  the page
• By default, this is set to true
• lt_at_ page buffer "none 16kb sizekb" gt
• Determines the size of the output stream buffer
• Defaults to 8kb
• Use with autoFlush
• lt_at_ page autoFlush "true false" gt
• When set to true, flushes the output buffer when
  it is full, rather than raising an exception

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JSP Page Directive (contd.)

• lt_at_ page errorPage "mypage/error_handler.jsp"
  gt
• Specifies the relative path of the page, where
  control would be transferred if any exceptions
  are thrown from this page
• The error handling JSP page should have its
  isErrorPage directive set to true
• lt_at_ page isErrorPage "true false" gt
• Marks the page as an error handler

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JSP Declarations

• Class and instance variables (of the generated
  servlet class) may be specified using the JSP
  Declaration tag
• lt! String name Web Applications"
• int index 10
• int count 0 gt
• Methods may also be specified
• lt!
• private int getNextIndex()
• return index
• gt

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JSP Scriptlets

• JSP scriptlets are defined as block of Java code
  embedded between a pair of
• tags, lt and gt.
• Example
• lt
• java.util.Date d new java.util.Date()
• out.println(d)
• gt

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JSP Expressions

• Useful for embedding the result of a Java
  expression in a HTML page
• The expression is encoded between the tags lt
  and gt
• The value of the expression is converted to a
  string and then displayed
• Conversion of primitive types to string happens
  automatically
• Example
• The date is lt new java.util.Date() gt

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JSP Implicit Objects

• When writing scriptlets and expressions, the
  following objects (called implicit objects) are
  available by default
• request javax.servlet.http.HttpServletRequest
• response javax.servlet.http.HttpServletResponse
• out javax.servlet.jsp.JspWriter
• session javax.servlet.http.HttpSession
• application javax.servlet.ServletContext
• exception java.lang.Throwable

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Reading inputs from Forms/URLS

• Remember that parameters are passed to Web
  applications via one of two methods
• GET method parameters are passed directly
  through the URL, encoded using the urlencoding
  method
• Quick to create and test can be created without
  a form
• Can be bookmarked
• URL shows in plaintext not secure
• POST method parameters are encoded and sent to
  the server separately from the URL
• Can only be created via forms (or advanced
  applications)
• Secure parameters cannot be seen
• Reading a single parameter via name
• String value request.getParameter(paramname)
• String values request.getParameterValues(para
  mname)
• / for multivalued parameters like
  checkboxes/multiple selectable lists /
• Better way using Beans - shortly

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JSP Session Example

• lthtmlgtltheadgtlttitlegtVisitor Count -- JSP
  Sessionlt/titlegt
• lt/headgt ltbody bgcolor"FFFFFF"gt
• lth2gtVisitor Countlt/h2gt
• ltpgtThis JSP page demonstrates session management
  by incrementing a counter each time a user
  accesses a page.lt/pgt
• lt!
• private int totalHits 0
• gt
• lt session request.getSession(true)
• Integer ival
• (Integer)session.getValue("jspsession.counte
  r")
• if (ival null) ival new Integer(1)
• else ival new Integer(ival.intValue() 1)
• session.putValue("jspsession.counter", ival)
• gt
• ltp align"center"gt
• You have hit this page lt ival gt
• timelt (ival.intValue() 1) ? "" "s" gt,
• out of a total of lt totalHits gt page
• hitlt (totalHits 1) ? "" "s" gt!lt/pgt

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JSP Actions

• Actions are tags that may affect the runtime
  behavior of the JSP or affect the current out
  stream they may also use, modify and/or create
  objects.
• JSP specification defines the following standard
  actions
• ltjspuseBeangt
• ltjspsetPropertygt
• ltjspgetPropertygt

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JSP Actions

• ltjspincludegt
• ltjspforwardgt
• ltjspparamgt
• ltjspplugingt
• New action types are introduced by means of
  custom tags

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What is a JavaBean?

• A Java class that (at a minimum)
• has an empty constructor
• has getters and setters for each of the
  properties in the class
• implements the serializable interface

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JSP Actions and Attributes

• JSP actions can define named attributes and
  associated values
• lt_at_ page import"People" errorPage"exception.jsp
  gt
• ltjspuseBean id"myperson" class"People" /gt
• lt myperson.setName("Ramesh") gt
• lth1gtMy name is ltmyperson.getName()gtlt/h1gt
• lt-- Let's now use the bean syntax --gt
• Name using Bean is
• ltjspgetProperty name"myperson" property"name"
  /gt

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Beans and HTML forms

• You may connect HTML form parameters to Bean
  properties
• ltjspsetProperty name"id" property"accountHolder
  "
• value "lt request.getParameter("accountHolder
  ")gt/gt
• There is a shorthand for the above
• ltjspsetProperty name"id" property"accountHold
  er" /gt
• This works if the property name was exactly the
  same as the form parametername

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Beans and HTML forms

• If the form parameter name and the property name
  do not match, then use the following variant of
  "jspsetProperty"
• ltjspsetProperty namemyperson" propertyage
  parammyage" /gt
• Another powerful variation of "jspsetProperty"
  examines all the parameter names from the request
  object and if some of them match with property
  names, it sets the appropriate properties
• ltjspsetProperty namemyperson" property"" /gt

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Beans and HTML (contd.)

• lt-- Trying the all powerful syntax --gt
• ltjspsetProperty name"myperson" property"" /gt
• Name is ltmyperson.getName()gt
• Age is ltmyperson.getAge()gt
• Weight is ltmyperson.getWeight()gt

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Including Files

• JSP supports two kinds of file inclusion
• Static (using the directive "include")
• Dynamic (or Request-Time)
• Static inclusion is specified using the "include"
  directive
• e.g., lt_at_ include file"header.html" gt
• In static inclusion, the contents of
  "header.html" are included in the output of the
  containing JSP file during the JSP page
  compilation
• If the contents of the "header.html" file change,
  these changes are not visible to the user of the
  containing JSP file
• Static inclusion is fast (because inclusion is
  done at compile time)

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Including Files (contd.)

• Dynamic inclusion is supported by the use of the
  tag "jspinclude"
• e.g., ltjspinclude page "news/headlines.jsp"
  flush "true" /gt
• Each time the containing JSP file is accessed,
  the JSP engine includes the contents of the
  latest copy of the file "news/headlines.jsp
• You may also pass parameters to the included
  file, e.g
• ltjspinclude page "news/headlines.jsp"
  flush"true"gt
• ltjspparam name"prefers" value"international"/gt
  
• ...
• lt/jspincludegt

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Forwarding Files

• A request to a JSP file may be forwarded,
  transparently to the user, to another JSP file
• ltjspforward page "target" /gt
• This is used to redirect request from one page to
  another page
• The calling JSP file relinquishes control to the
  forwarded page
• The calling JSP cannot send any data back to the
  browser before invoking this tag
• If data had already been sent by the calling JSP,
  invoking the "jspforward" tag causes an
  exception to be thrown

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Forwarding Requests

• You may also pass parameters to the forwarded
  page
• ltjspforward page"catalog.jsp" /gt
• ltjspparam name"color" value"red"/gt
• ...
• lt/jspforwardgt
• Parameters passed in this fashion may be accessed
  by the forwarded JSP (catalog.jsp) by the
  following call
• request.getParameter("color")

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Forwarding Requests

• Request forwarding is typically used for
  authentication
• lt
• if(request.getParameter("login-info") null)
• gt
• ltjspforward page"login.jsp"/gt
• lt
• else
• / Generate Error message no login /
• gt

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Summary

• JSP JDBC provides a stable and well-tested
  platform for 3-tier web application design
• Supports all major databases and all platforms
• With Servlet compilation, performance is high
• Many major applications like Wiki, major
  Government/Funding organizations like NSF are
  running on Java/JSP technology.
• Web services are well-supported
• J2EE provides a well-designed software design and
  development platform for enterprise systems.