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					Distributed Web Systems


                                  Laboratory exercises
                    Using session tracking and working with cookies

Learning goals:

    Learn to use servlet session tracking to store the servlet state between HTTP requests
    Learn to set and access cookies.
    Understand differences between persistent and session cookies.


What to do:

    Create a new Ant project directory for this lab with the “src” and “web” sub-
     directories. Put the Ant build files from the course web page into this project
     directory.

    Write a servlet that performs the following functions (remember to use your own or
     provided helper classes, such as “ServletUtilities”, to speed up the development):

          a. Reads two input parameters submitted by the user: “product” and “quantity”.
          b. Obtains the contents of the customer’s shopping cart from the servlet session.
          c. Adds the given quantity of the specified product to the shopping cart.
          d. Displays a “thank you for shopping” page with the shopping cart contents to
             the user.
          e. Updates the shopping cart contents in the servlet session.

          A simple and sufficient for this lab way to store the shopping cart contents is an
          HTML-formatted text string. When the cart is empty, the string equals to “”.
          When we add a new product to the cart, we simply append the following text to
          the string: “\n<BR> product_name      Quantity: product_quantity”.

          In this case, if we insert our cart string into an HTML document, we will get the
          following in the browser:

               product_name1     Quantity:     product_quantity1
               product_name2     Quantity:     product_quantity2
               ...
               product_nameN     Quantity:     product_quantityN

          Basically, we get something looking like a receipt. Of course, you can and are
          encouraged to use fancier and nicer looking HTML formatting here.

          Remember to check the correctness of the input data.

    Remember to place all your .java sources into the “src” sub-directory, so that Ant
     could compile them automatically.
Distributed Web Systems


    Create a web application deployment descriptor for your application and put it into
     “web/WEB-INF”. You can modify the descriptor from the previous lab or the one
     available on the course web page. Choose some appropriate URL pattern for your
     servlet, e.g. “/AddToCart”.

    Create an HTML page for a shopping
     catalogue. The page should list a set of
     products and for each product provide a
     text input field to enter the quantity and an
     “Add to cart” button.

      To achieve this, you should create a
      separate form in your page for each
      product. Each such form should have an
      input text field named “quantity” for
      entering the amounts, and a hidden field
      named “product”. The value of this hidden
      field should be set to the product name.
      This way you can pass the product name to
      your servlet without cluttering the visible
      text on the page. See the example HTML
      fragment below and an HTML page in the
      illustration (hopefully, your catalogues will
      look much prettier!)


           <H2>Laptop computer. Price $3000.</H2><P>
           Very powerful yet light and slim.
           <FORM ACTION="AddToCart">
               <INPUT TYPE="HIDDEN" NAME="product"
                                     VALUE="Laptop computer."><BR>
               Quantity: <INPUT TYPE="TEXT" NAME="quantity">
               <INPUT TYPE="SUBMIT" VALUE="Add to cart">
           </FORM>

      For the form action, you should use a URL matching the URL pattern for your
      “AddToCart” servlet (whatever you used in your “web.xml”).

    Put this HTML page into the “web” sub-directory and name it as “index.html”, so that
     it becomes the default page for your web application.

    Compile and deploy your application using Ant.

    Verify the functioning of your servlet. Try to populate your shopping cart, then
     restart the browser and see how this affected the shopping cart contents. Explain such
     behaviour.


So far so good! Now you can use servlet sessions to keep your application state between
HTTP requests. Let’s focus some more on cookies now.
Distributed Web Systems


    Write a servlet to do the following:

          a. Create two cookies: one session cookie, and one more persistent cookie that
             should be stored for at least an hour. Name these cookies appropriately and
             assign some test values to them.
          b. Request the browser to store those cookies;
          c. Obtain the list of all currently active cookies and print their names and values;

          If your lab time is running out, you may use the ready code for this lab from the
          course web page. However, do spend time in this case familiarising yourself with
          that code.

    Add this servlet to your application descriptor and create an appropriate URL
     mapping for it there.

    Re-deploy your application. That is, do “ant remove” followed by “ant install”.
     Remember that all Ant commands must be issued in your project directory (where the
     Ant build files are).

    Call the servlet two times and explain its output.

    Now restart your browser and again call your servlet two times. Explain the obtained
     results.

    You are done! Remove your application.

				
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