Akka Streams

Exercise 1

A few minimal exercises to get you started:

• Print the numbers 1 to 100 (generate them with a Source, print them with a Sink)
• Print the squares of the numbers 1 to 100 (1, 4, 9, 16, etc…)
• Print the total of the squares of the numbers 1 to 100

Exercise 2

Let’s do something a bit more practical. Here are four exercises involving reading the contents of a file.

Read at the contents of /usr/share/dict/words and do the following things (tackle each problem separately in a different code sample):

• Print the contents of the file to stdout. Use the following to get the file:

  FileIO.fromPath(Paths.get("/usr/share/dict/words"))

• Count the words in the file (235886 on my machine) and return the count after running the stream.

• Count the number of vowels in the file (889151 on my machine) and return the count after running the stream.

• Print adjacent pairs of words that have the same length (tip: use source.sliding()).

• Write the pairs of words from the last exercise out into a new file (tip: use FileIO.sink())

Exercise 3

We often need to fold over streams to accumulate results while only having access to a single item at a time. Here are a few exercises along these lines (see src/main/resources/medals-expanded.csv and Medal.scala):

• Write a method athletesForTeam that accepts a three-letter team code and returns the list of athletes who competed for that country.
• Write a method medalsForTeam that accepts a three-letter team code and returns the number of bronze, silver, and gold medals .
• Write a method leaderboard that returns a leaderboard of athletes by total medal count.

Exercise 4

Let’s practice interfacing with a database. We’ll use MongoDB:

1. Print all the medals from the database
2. Print the number of gold, silver, and bronze medals won by each country
3. Create a second collection, totals, containing:
   1. the name of each country;
   2. the total number of gold, silver, and bronze medals.