File Input/Output

In this lab you'll take coffee orders by reading them in from a comma-delimited file, e.g.:

small,milk,sugar
large,none,none
medium,half-n-half,splenda
medium,milk,none

Overview

Before diving into the details, let's take a high-level view of what you'll need to do. For each line in the file, you'll need to:

1. Read the line from the file into a String variable
2. Split the line into its parts by using the split() method on String
3. Instantiate a CoffeeOrder based on the parts that you read
4. Display the coffee order
5. Loop until you've reached the end of the file

Step 1: Create the File on Your Machine

Download this file and copy it into the resources directory underneath your /src/main/ directory. Note: you might need to create the resources directory first.

Step 2: Create a New Main Class

• Create a new Java class, FileApp, with a new public static void main(String[] args) method.

  • Leave the existing App.java alone.

• Put the following code into the main method of the new class:

  String fileName = "orders.csv";
  try {
    URL file = FileApp.class.getResource(fileName);
    BufferedReader reader =
        Files.newBufferedReader(Paths.get(file.toURI()));
  } catch (IOException e) {
    e.printStackTrace();
  } catch (URISyntaxException e) {
    e.printStackTrace();
  }
  

• Run FileApp's main() method and make sure it completes without an exception.

• If you get an exception (e.g., NullPointerException), then you don't have the orders.csv file in the right place.

  • Make sure the orders.csv is in src/main/resources inside your project folder.

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Step 3: Loop Through All Lines

Check to make sure you can read the file correctly:

• Write a while loop that reads each line and then prints it out.

  while

  Documentation for the while loop (and other loops) can be found here: https://books.trinket.io/thinkjava/chapter7.html

• Make sure you check if the line is null, so you can use a break to exit the loop.

  readLine

  JavaDoc for the readLine method are here: https://docs.oracle.com/javase/8/docs/api/java/io/BufferedReader.html#readLine--

• Run FileApp and make sure you see the contents of the file displayed and get no exceptions.

How might you write this as a test?

Instead of relying on watching the code output the file contents to the console, how might you write this in a testable way?

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Step 4: Break Apart Each Line

Try to write test-first

Try to figure out how to write the test for each step below, instead of just heads-down writing code.

Now that you can read lines one at a time, let's look closer at what each line looks like:

small,milk,sugar

This is a comma-separated set of instructions of what coffee order to create. The above example would create a Small coffee, with Milk, and Sugar.

• Using the String.split() method, break apart each line that you read into its 3 parts.

  String.split JavaDoc

  JavaDoc for this method is here: https://docs.oracle.com/javase/8/docs/api/java/lang/String.html#split-java.lang.String-

• For each string part, convert it to the appropriate Enum or String, as necessary

  • This is similar to how you handled input from the user in a prior lab.

• Instantiate a CoffeeOrder from the parts that you split

  • Use array access for what you got from String.split(), e.g.:

    String[] parts = line.split(","); // comma-separated
    String size = parts[0];
    String creamer = parts[1];
    String sweetener = parts[2];
    

• Display the order (using display() on the CoffeeOrder)

Step 5: Try it!

Once you've completed the above steps, try it out by running the FileApp's main method and it should all work with no exceptions.

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References

Chapter 10 of the Effective Java book is about how to do exception handling well.

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Once you've completed the above steps, check in with the instructor to review your code.

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