C$50 Finance (Java Edition)

A Java (Spring Boot) implementation of the C$50 Finance problem set from cs50x

Introduction

You've mastered C and learned the basics of Java. Now it's time to apply that knowledge in a modern application environment. We'll learn Spring MVC (via Spring Boot) and Hibernate annotations (for storing objects in a database), while re-implementing our old friend, C$50 Finance.

Getting ready

We need to prep our environment before diving into the code.

• Install MAMP, if you haven't already. We'll use MAMP as a convenient way to fire up and inspect our MySQL database (via either phpMyAdmin or Sequel Pro, which is bundled with MAMP). We won't use the Apache or PHP portions of the app for this project, but having them around isn't a bad thing.
• Fire up MAMP and open either phpMyAdmin or Sequel Pro (default user:pass is typically root:root or root:(blank)). Create a database called cs50_finance_java, a user jharvard with password crimson, and grant jharvard all privileges on your new database (for localhost only).
• Fork this repository.
• Fire up IntelliJ, and create a new project via File > New > Project From Version Control. Select your new fork from the popup, and proceed with project creation.

Getting started

There's a lot that's new here, including a Java web app using the MVC pattern, object persistence via Hibernate, Spring Boot, Maven, Thymeleaf templates, and more. Fear not. You'll get used to it all with a bit of guidance, by reading the code base, and referencing documentation online.

Once you have your new IntelliJ project, you can start up your web app by opening the Maven panel and expanding Plugins > spring-boot. There you'll see spring-boot:run as an option. Right-click on it and select Run finance[spring-boot:...]. The app will spark to life and you'll see a flurry of log message in the Run panel. If you see an exception stack trace, something went wrong. The most common issue here is that your database isn't running. Make sure it's actually running. If that's not it, try to get some hints from the stack.

Once the app starts up cleanly, point your browser at http://localhost:8080 and you should see the C$50 Finance login page.

Have a look around at the code. You'll see that it's all in the net.cs50.finance package (src/main/java/net/cs50/finance/), with sub-packages for models and controllers, and a couple more below that. Our templates are stored in src/main/resources/templates/ with the Tymeleaf extension of .html since they're "natural templates" (that is, templates that can still be displayed in a browser without any additional rendering engine).

What to do

• First, register a user or two for testing via the register link on the login page. (Notice how we've already implemented that one for you!)
• You have a few TODOs left in the comments (open your TODO panel in IntelliJ for a handy guide, and to clear them off as you go). The first is to implement quote lookup. You'll find the request handler for this action in StockController.java, and quote_form.html and quote_display.html. Take it from there, using the parameters already put in place for you in the template.
• We failed to make the symbol field of StockHolding.java case-insensitive, which will cause unintended results when buying and selling. Fix this by updating the appropriate constructor for the StockHolding class to make the symbol either always be upper or lowercase (your choice). You'll also have to update the static buyShares and sellShares methods in the same class.
• Implement buy and sell. You'll find request handlers in StockController.java, relevant model methods in StockHolding.java, and a shared buy/sell template in transaction_form.html and transaction_confirm.html. (Read the controller code in detail to see how we manage this shared template, which would have been messy in PHP.) Note that you're making changes that should be persisting data in the database, so be sure that's happening correctly before checking this one off your list. You'll have to deal with a StockLookupException in some cases. Your controller should try/catch the affected calls and respond appropriately (hint: see AbstractFinanceController.displayError and it's usage in other locations within the project).
• Now that you can buy and sell, let's make sure our users can't buy indefinitely (we forgot to give them a cash limit). Add a cash field to the User model class, making sure to include the proper persistence annotations. Then, update the user's cash on buy/sell requests, and handle a request to buy that exceeds available funds appropriately.
• Display the user's stocks in a table. You'll find some code already in place in PortfolioController.java and the portfolio.html template. You should display the following fields for each stock in the template: display name (use Stock.toString()), number of shares owned, current price, and total value of shares owned. Format the currency values appropriately, with 2 decimal places. You may find the th:each Thymleaf tag useful here.

Resources

Spring Boot/General/Other

• Spring Boot Reference Guide
• Maven (Wikipedia)
• Thymeleaf User Guide

Data/ORM/Hibernate

• What is ORM (Object-Relational Mapping)? (Wikipedia)
• The JPA (Java Persistence API) (Wikipedia)
• Spring Data JPA Reference (See section 2.4 for info on DAO query methods)
• ORM in Spring (Note that the XML configuration sections here aren't relevant to Spring Boot, but there's some useful info on DAOs in Spring)
• JPA Annotations Reference