CS636 Practice Final Exam, Spring, 2021            NAME:_________________________                      

Open books, handouts, solutions, browser use, etc., but not conversations with others..

Problems are marked with points, Total points = 150. 

Note: this exam is too long to be an actual final exam.

 

1.      (15) Important Examples

a.       In the Download application of Chapter 7, available in project ch07downloadS, there are these notable components:

A servlet, DownloadServlet.java     M  V  C

File-accessing code, UserIO.java    M  V  C

Various JSP files                    M V  C

This is an MVC application, although not as layered as our main projects. Classify these parts of the application by circling M for model, V for view and C for controller.

 

b.      The Cart application of Chapter 7, available in ch07cartS allows a user to manipulate the contents of a shopping cart, adding, removing, and updating its items on various requests.  Through what mechanism provided by tomcat (and other application servers) is an app allowed to keep around an object in memory through the various requests by one user. Specifically:

 

Mechanism name:

Brief description of how it works, and what software in involved:

           

 

2.       (15) Concurrency Suppose a MVC web application (pizza3 or music3) running in tomcat has 6 user sessions active, and of these, 3 (with all different users) are doing concurrent requests, and of these, 2 are doing concurrent transactions at this moment. 

 

a.       How many JDBC Connections are active and communicating with the database?

b.      What object manages these connections as a group for the app, optimizing short-term use of JDBC connections? Specifically:

 

Class name of object:

What code creates this object:

 

c.       How many Session objects are in tomcat’s memory?

 

d.      Is there any worry that the two requests with concurrent transactions for different users of pizza3 will be sharing a PizzaOrder object in memory? Explain.

 

3. (30) Application Design and Layers. Currently the products in the music project are unchanging. Suppose you have been asked to add an admin capability to change the price of any specific product. This change will make Products mutable, but don’t worry here about those mutable objects being in the presentation layer.

 

a.       Explain why

 

void changePrice(Product updatedProduct) throws ServiceException

 

 is not a good choice for a new service layer method. Hint: what code would provide the “updatedProduct” object?

 

 

 

 

b.      Show a good choice for the changePrice service method signature.

 

 

 

 

c.       Describe any changes needed to the DAO API for your design, or explain why none are needed.

 

 

 

 

d.       Describe any changes needed to the database schema for your design

 

 

 

 

e.       In your design, is there a new transaction?  If so, what does it do?

 

 

 

(30) 4. The Database Model and SQL.

Suppose we want to enhance the music project to allow users to submit votes (or “likes”) for songs, i.e., tracks.  A user vote is submitted by a certain registered user for a certain track. A user can’t undo their vote once made, and each user can only vote at most once for each track, that is, additional votes for the same track and user will be just ignored. We also want to record the time the vote was submitted (the one that counted, not discarded duplicate votes).

 

a.       Give the create table statement for your new vote table, complete with any appropriate foreign key constraints.

 

 

 

 

 

 

 

 

 

 

b.      Show the new Vote domain class, with references to related domain objects corresponding to any foreign keys you specified above. As usual, you can put “// getters and setters…”

 

 

 

 

c.       Write SQL to find the number of votes each CD has received, that is, summed over all their tracks.  List CD product code and number of votes.

 

 

d.      Write SQL to find users (by their email addresses) who have voted for a track but never downloaded that track.

 

 

 

 

 

(30)  5.  Consider the application scenario from the practice midterm. Suppose you are automating operations for a store selling PCs.   All PCs of a certain model number are equivalent as far as buyers are concerned, but the store wants to sell them in FIFO (first-in, first-out) order so that no box gets too worn-looking.  Each PC has a model number (int), serial number (10-char string), vendor id (int), and delivery date (int day number, when the PC arrived at the store.)  At sale-time, the salesperson will enter a model number and get back the serial number of the system to sell (in case of ties for oldest, any one of the oldest.)

 

1. Write a business layer API that allows entry of new PCs by inventory clerks and another call to retrieval of the next one to sell by salespeople.  Don’t forget the exceptions.

 

 

 

  

2. You are asked to write a web app for the salesperson to use. It has a form page with a form with method=”POST” action=”lookupPC.html” and an input text field with name “model” for the model number. It also has a result page found_pc.jsp, also in the top-level directory. Following our Spring Boot webapp design, we would write a InventoryController that handles the form submission (and other actions). Assume all the infrastructure code is there: SBApplication,  CommandRun, etc. Write a controller handler method, with appropriate annotation, to handle the URL from the form submission, calling your API and forwarding to the result page. Don’t worry about errors here. Assume the InventoryController class has a field inventoryService with annotation @Autowired to your service object, i.e., the singleton object created for the API you wrote for part a.

 

3. Write found_pc.jsp, using data you attached to the request object in your handler method, or attached to the Model object, knowing that the DispatcherServlet will attach it to the request object.