BMIS 289: Spring 2002 Gonzaga University

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BMIS 289 Spring 2002Gonzaga University

• Class 07Request/Response, Sessions/CookiesAr
  rays

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Agenda

• Program 5 Overview
• Data type conversion note
• Request/Response
• Sessions Cookies
• Arrays
• Midterm Overview

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Program 5

• This program has three distinct parts
• 1. Ask how many checks the user wants to input.
• 2. Generate that number of check input forms.
• 3. Collect the information from the check input
  forms and compute a new check register balance.

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Program 5 Step 1 (page 1)

• This is a simple input form (no different than
  what weve done before).
• We capture three separate fields
• Account owners name
• Beginning balance
• Number of checks to input (1-5)

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Program 5 Step 2 (page 2)

• First we retrieve the form information from page
  1, store them in variables, and then write them
  as hidden HTML input form fields in our page 2
  form.
• We will need this information in page 3 later.
• Using hidden form fields assures us that the data
  will get passed on to page 3 when the page 2 form
  is processed (but hides it from the user)

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Program 5 Step 2 (page 2)

• On page 1 we asked how many checks the user
  wanted to input, so now we must generate those
  input fields.
• Each check has common input fields (check number,
  amount, deposit/check, etc).
• Since we know the number of check inputs we need
  to generate (from page 1) this action would be
  perfect for a loop.
• The only problem is that the HTML form fields
  must have unique names.

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Program 5 Step 2 (page 2)

• If we were hard coding this page we might choose
  to name each field like so
• CheckNumber1, CheckNumber2
• CheckAmnt1, CheckAmnt2
• CheckDate1, CheckDate2
• Our loop code could accomplish the same thing,
  for example
• FOR count1 to 5 current_cnum check_number
  count Response.Write
  name current_cnum NEXT

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Program 5 Step 3 (page 3)

• On this page we must echo the check inputs from
  page 2 AND calculate a new balance for the check
  book.
• Again we must perform a loop, but this time we
  want to extract the information entered into the
  check fields (instead of generating the fields).
• As on page 2, each time through the loop the a
  unique html field name must be generated. Only
  now we pass that field name into Request.Form()
  to extract the corresponding input.

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Program 5 Step 3 (page 3)

• Once we have extracted the inputs for a
  particular check we then output the check
  details, and compute any changes to the balance.
• If the check was a deposit then add to the
  running balance.
• If the check was not a deposit then subtract from
  the running balance.
• When the loop ends we will have our new balance.

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A note about data type conversion
data_type_conversion.asp

• We would assume that this code converts the
  balance variable to the currency data type

TypeName(balance) "
" balance
ccur(balance) Response.Write TypeName(balance)
"
" balance 12.00 Response.Write
TypeName(balance) "
"
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Data type conversion cont.

• The actual output looks like this
• The first conversion does, indeed, change the
  data type of the variable to Currency.
• However, when 12.00 is assigned to the variable
  ASP automatically converts it to double.
• To avoid these misconceptions you should do data
  conversion on every line that requires it.

EmptyCurrencyDouble
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Request Response Refresh

• Recall that HTTP consists of two forms of
  communication the Request and Response.
• HTTP Request
• Message going from Browser ? Server
• HTTP Response
• Message going from Server ? Browser
• Weve already covered methods like Response.Write
  and Request.Form, but there are others

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QueryString

• A querystring is simply a collection of variables
  and their associated values that are appended to
  the end of a URL.
• Take this example URL
• http//gonzaga.edu?variable3
• Here we have one querystring variable (called
  variable), with the value 3, appended to the
  end of the URL http//gonzaga.edu

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QueryString cont.

• A querystring is indicated by adding a ? to the
  end of a URL and then appending variable/value
  combinations.
• A querystring can contain multiple variables
• http//gonzaga.edu?v13v2hello
• Here we have two variables v1 and v2 with values
  of 3 and hello respectively.
• Notice how the symbol was used to separate
  the two variables.

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Making QueryStrings

• There are three primary ways to create URLs with
  query strings
• User types the query string manually into the
  browser address bar (not likely to happen).
• Embed querystring into HTML directly.
• Use GET method when posting form data.
• Embedding a querystring into HTML

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Making QueryStrings cont.

• Using the form method GET
• If you use GET, instead of POST, as the value to
  the METHOD attribute of an HTML form then your
  browser will automatically generate the
  querystring to send to the server.
• typetext nameusername
  typesubmit valuesubmit
• If I enter cfukai into the username text field
  then this querystring will be appended to the end
  of process.asp
• ?usernamecfukai

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Getting QueryString Values

• A querystring is very similar to using a form to
  POST data to an ASP page.
• Likewise, retrieving the data from a querystring
  with ASP is very similar.
• Request.QueryString()
• me)
• This is a lot like Request.Form()

RequestQueryString.htm, RequestQueryString.asp
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The Buffer

• In ASP, the buffer is a temporary storage space
  on the server where an HTML stream is held before
  being sent to the client.
• When you add into the buffer it is added to the
  end, like a queue. The Response object has
  properties and methods we can use to manipulate
  the buffer
• Buffer, Flush, Clear, End

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Response.Buffer

• This is a property than can have two values
  true, false
• Must be set before any HTML is written to the
  browser.
• It is used to tell ASP that we will be manually
  controlling when the HTML stream is sent back to
  the browser.
• Response.Buffer is true by default in Win 2000,
  false by default on NT4.

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Buffer Methods
Buffer_manip.asp

• Flush this is a method that sends any already
  buffered HTML directly to the browser.
• After it is called ASP continues processing the
  rest of the page and returns anything else.
• Clear erases any already-buffered HTML, but not
  any HTTP Response Headers.
• End stops processing of the ASP script and sends
  any buffered output to the browser.
• See example on page 274-275.

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Redirection
Redirect_Menu.htm, Redirect.asp

• Sometimes we want our code to redirect its
  execution to another page.
• Syntax Response.Redirect
• Response.Redirect ends the execution on the page
  that called it and transfers it to the page that
  is called.
• Note this does not transfer variables or any
  other data from our code.
• Execution never returns back to the page that
  called Response.Redirect.

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Redirection

• Redirection is often used on login pages.
• We could have a login page that would redirect to
  an error page if the user failed to login
  appropriately.
• Example
• mypassword
  Then Response.Redirect error.asp End If

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Web Applications

• A web application is a program that is written
  for the web.
• A web application is like any other program. The
  primary difference is that the browser is the
  interface.
• Web applications are made up of several pages,
  databases, and other support files that act as
  one application.

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Maintaining State

• The key to writing any sort of web application is
  identifying every unique user of our application
  and tracking them, and their actions, as they
  move from page to page.
• AKA maintaining state
• Unfortunately, HTTP was designed to be stateless.
  All it really cares about is delivering HTML.
• ASP provides some tools to overcome this
  weakness
• Cookies, Sessions, Application Variables

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Cookies

• Cookies are simply small text files that are
  written to a users hard drive by their browser.
• They contain variables and their associated
  values.
• For example, many sites offer a auto-login
  feature. This is accomplished by
• Writing a cookie to the users hard drive that
  contains the valid user name and password they
  entered.
• When the user returns to the site an ASP page
  checks to see if a cookie it wrote exists on the
  users hard drive. If it does, ASP can then take
  the information from the cookie to login
  automatically.

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Cookies cont.

• Domains (e.g, gonzaga.edu) and servers can only
  read cookies they have set.
• So gonzaga.edu cant read cookies set by cnn.com
• ASP writes cookies using the Response object, and
  reads cookies using the Request object.
• Cookies are very popular because they are stored
  on the client (and not the server), but a user
  may elect to disable cookies in their browser.

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Setting A Cookie

• Syntax
• Response.Cookies()
• Where is the name of the cookie,
  and is the value that variable will have.
• Example
• onse.Cookies(Email) Email

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Reading From A Cookie
Cookie1.asp, cookie2.asp, cookie3.asp

• Syntax
• Request.Cookies()
• Where is the name of a cookie.
• This method returns the value that is currently
  in that cookie.
• Example
• According to the cookie, your email is Request.Cookies(Email)

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Persisting A Cookie

• By default, when you set a cookie the browser
  automatically destroys it once the browser is
  closed.
• To save it on the users hard drive (the cookie
  jar ?) we need to set an expiration date for it.
• Example
• cfukai_at_gonzaga.edu Response.Cookies(Email).Ex
  pires Date 30
• This code sets a cookie that will persist for
  about 30 days from the date it is set.
• Date is the current date on the server.

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Deleting A Cookie

• To delete a cookie set the expire date to any
  date prior to the current day.
• Example
• 30
• This method might fail though, depending on how
  the user has their time configured, but most
  users should have their machines configured to
  within a month of the actual date.

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Sessions

• Sessions are a way for ASP to track every unique
  user of our web application as they move from
  page to page.
• A users session begins when they access their
  first .asp page on the web site. The users
  session continues as they move from page to page.
• In ASP we use the Session object to add
  information about a users session and read
  information from it.

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What We Can Do With Sessions

• Sessions let us do three primary things
• Store information about each users session
  (e.g., form inputs) using session variables.
• Be notified when a user session begins.
• Be notified when a user session ends.

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Setting A Session Variable
Session1.asp, Session2.asp, Session3.asp,
Session4.asp

• We dont have to declare session variables.
• The first time we use them they are automatically
  declared.
• We can access session variables as long as the
  users session is active.
• Example
• Page1.aspRequest.Form(Email)
• Page2.aspYour email address is Session(Email)

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Global.asa

• When we talk about sessions and web applications
  we need to consider a file called global.asa
• This file includes event handlers, which are sub
  procedures that allow us to run code when certain
  events (like a user session beginning) occur.
• The global.asa file must be placed in the root of
  the web applications virtual directory.

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Global.asa Example
Global.asaPage.asp

• Global.asa
• Page.asp

Sub
Session_OnStart Session("30DaysAgo") Date -
30 End Sub

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Session Event Handlers

• There are two separate session event handlers
  that can be used in global.asa
• Session_OnStart
• Session_OnEnd
• The Session_OnStart handler is run every time a
  user session begins on the web server.
• The Session_OnEnd handler is run every time a
  users session ends.

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Ending A Session

• There are two ways a users session can end
• The session times out
• The session is abandoned
• Timeout
• If a user is inactive for longer than a
  pre-determined period of time then the session
  automatically ends.
• This time can be set through the Session.Timeout
  property
• Session.Timeout 30
• This line sets the session time out to 30
  minutes, by default it is 20 minutes.
• Abandon
• A session can be manually ended by calling the
  Abandon method of the session object

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Application Variables

• Application variables are similar to Session
  variables. Once you set an application variable
  it is available on any page in your web
  application.
• The difference is that application variables can
  be accessed by all users of the web application.

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Setting App. Variables in Global.asa

• Typically, application variables are set in
  global.asas Application_OnStart event handler
• Sub Application_OnStart Application(MainPhone)
  555-5555End Sub
• This application variable can be accessed on any
  page in the web app
• Phone

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Setting App. Variables In A Page

• Setting application variables in an ASP page is a
  little different.
• Suppose we let a user change the application
  variable and while theyre doing that their
  machine locks up.
• While the web server was waiting for the locked
  client to finish changing the application
  variable another user could change the
  application variable, causing data corruption.

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Setting App. Variables In A Page Cont.

• To avoid this we want to lock the application
  variable were changing (so no other clients can
  change it), change it, and then unlock it
  again.
• Example
• 555-5551 Application.UnLock

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Application Event Handlers

• Also, like sessions, the application object has
  two event handlers in global.asa associated with
  it
• Application_OnStart
• Application_OnEnd
• Application_OnStart is called the very first time
  a user accesses the web application.
• Application_OnEnd is called immediately after the
  last active session within that application ends.

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Break
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Arrays

• Variables are handy ways for storing individual
  items of data, but theyre not so good if you
  want to store a lot of related information.
• An array is the programming construct we can use
  to store related data.
• Arrays are simply a collection, or a list of
  variables.

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Arrays Cont.

• Arrays look a lot like normal variables but they
  have two separate parts to their name
• The first part is the name itself, which is the
  same for every variable in the array.
• The second part is a number that is to the right
  of the array name and is surrounded by
  parenthesis. This number is used to access
  individual items in the array.
• Suppose we had a list of scores called Score
• The first score would be Score(0), the second
  score would be Score(1), the third Score(2),
  and so on

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Array Indexes

• The number to the right of the array variable
  name is the array index.
• The index is how we reference individual
  variables in the array.
• By default array indexes start at zero. So the
  first item in any array would be at index 0
• So if we had an array to hold the names of the 50
  states the 50th state would be at array index 49.

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Array Example

• Suppose we wanted a list of 5 scores. Heres how
  the code would look

20Scores(2) 15Scores(3) 11Scores(4) 20
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Walking Thru The Array Code

• Dim Scores(4)
• Declares an array with 5 individual elements
  (variables) in it.
• By default, VBScript will assign the first
  variable the array index of 0, the next 1, and so
  on.
• Scores(0) 19
• Take the first variable in the array and put the
  value 19 in it.
• Notice how this is just like assigning a value to
  an ordinary variable. Array variables are just
  like regular variables, except they are related
  to each other by the array name (Scores in this
  example).

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What Can You Do With Array Variables?

• Anything you can do with a normal variable (and a
  little more, as we will see later).
• You can output it
• Response.Write Scores(0)
• You can process it
• PercentScore Scores(0) / n
• You can convert it
• IntScore Cint(Scores(0))
• Arrays can hold any type of variable (numbers,
  strings, objects, etc).
• The real power of arrays is when you combine them
  with loops.

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Looping Thru Arrays

• Arrays can be quickly traversed using FOR loops.
• The ASP function Ubound() gives us the largest
  index in an array.
• In other words, it gives us the size of the
  array.
• A FOR loop uses a counter variable to iterate. We
  can use this counter variable to represent the
  array index and gain access to individual array
  items.

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Processing An Array Cont.
Output_onedarray.asp

• Taking the previous code example of an array of
  scores, we could output every score in that array
  using a FOR loop

Dim i For i0 to Ubound(Scores) Response.Write
Scores(i) "
" Next
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Breaking It Down

• Dim iFor i0 to Ubound(Scores)
• Declare a variable that will server as the loop
  counter and array index.
• Loop runs from 0 to 4 (the first index starts at
  0 and the last index is 4).
• Response.Write Scores(i)
  
• The loop code output the value at array index
  i
• Next
• Increment the array index / counter variable

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Multi-Dimensional Arrays

• Up until now we have focused on single-dimension
  arrays. Which are essentially just lists of
  variables, consecutively stored in memory.
• But what if we wanted to store information like
  this
• The solution is to use a multi-dimensional array.

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Multi-Dimensional Arrays Cont.

• The election results in the previous slide are an
  example of a two-dimensional array.
• A two-dimensional array is just a table of data.
  Remember that tables have rows and columns.
• A two-dimensional array is declared like this
• Dim TwoDArray(num_rows, num_cols)

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Two-Dimensional Array Code Ex

• Here is the code to create the election results
  table we showed two slides ago

Dim ElectionResults(2, 1) ElectionResults(0, 0)
"Gore" ElectionResults(1, 0)
"Bush" ElectionResults(2, 0) "Other" ElectionRes
ults(0, 1) "50,996,116" ElectionResults(1, 1)
"50,456,169" ElectionResults(2, 1) "3,874,040"
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Looping Thru 2-Dimensional Arrays

• A FOR loop is used to process a 2D array just
  like it is used to process a 1D array.
• The difference is that we need two loops
• One FOR loop to process each row in the array.
• One FOR loop to process every column (cell) in
  a given row.
• Psuedocode would look something like this
• For row0 to numrows 1 For col0 to numcols
  1 output 2darray(row, col) NextNext

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Ubound in 2D Arrays

• How do we determine the number of rows and
  columns in a 2D array?
• The ubound function has a second parameter,
  dimension, which tells ubound which dimension of
  the array you want to get the highest index from.
• If no dimension argument is provided VBScript
  assumes the 1st dimension (the row)
• Numrows Ubound(ElectionResults) 1
• Numrows Ubound(ElectionResults, 1) 1
• The number of columns is the second dimension
• Numcols Ubound(ElectionResults, 2) 1

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Iterating through a 2D Array
2dray.asp

• Assume this code is processing the
  ElectionResults array

for row 0 to ubound(ElectionResults) for col0
to ubound(ElectionResults, 2) Response.write
ElectionResults(row, col) " " next response.wr
ite "
" next
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Breaking It Down

• for row 0 to ubound(ElectionResults)
• This is the outer loop, it iterates through the
  rows in the array.
• for col0 to ubound(ElectionResults, 2)
• This is the inner loop, it iterates through the
  columns in every given row
• Response.write ElectionResults(row, col) " "
• The inner loops code.
• It outputs a particular columns (cell) value.
• Note that the outer loop iterates 3 times, and
  the inner loop has 2 iterations per execution of
  the outer loop.

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Dynamic Arrays

• As we have seen, an array has to be declared with
  a given size. But what if we dont know how many
  array variables well need before declaring?
• Answer use a dynamic array.
• A dynamic array is an array whose size (number of
  array variables) can change as we move through
  our code.
• Generally we should avoid using these because
  they can be a performance drain (but sometimes
  there is no other way to solve the problem).

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How NOT To Do Dynamic Arrays

• Most new programmers assume code like this is
  legal
• This is not legal code, and it will generate a
  compiler error.

Scores(NumElements)
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How To Make A Dynamic Array

• There are two parts to creating a dynamic array
• Declare it
• Size it
• Declaring a dynamic array
• Dim Scores()
• You MUST declare the array with no size at first.
• Size the array.
• NewArraySize 10ReDim Scores(NewArraySize)

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Notes About Dynamic Arrays
DynamicArray.asp

• When you size a dynamic array (i.e., you use the
  ReDim keyword) all the elements that are already
  in the array are destroyed.
• To keep whats in the array when you resize it
  use the Preserve keyword
• Dim Scores(4)code that sets the 5 scoresReDim
  Preserve Scores(9)
• After we resize the array there are 5 new array
  variables added onto the end of the list of 5
  scores that are already there.

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Midterm Next Week

• Review the class lecture PowerPoints and all the
  chapters youve been assigned so far.
• Combination of multiple choice, fill in the
  blank, true/false, and short answer (including
  writing code).
• Study guide will be emailed to you later this
  week.
• Program 6 assignment will be handed out next
  Wednesday (it will relate to the material we
  covered today).

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ENDStudy for Midterm