Scala, Java, Unix, MacOS tutorials (page 1)

This is an excerpt from the Scala Cookbook, 2nd Edition. This is Recipe 3.12, Parsing Strings Into Dates.

Problem

While using Scala (2 or 3), you need to parse a string into one of the date/time types introduced in Java 8.

Solution

If your string is in the expected format, pass it to the parse method of the desired class. If the string is not in the expected (default) format, create a formatter to define the format you want to accept.

This is an excerpt from the Scala Cookbook, 2nd Edition. This is Recipe 3.11, Formatting Dates in Scala.

Problem

While using Scala (2 or 3), you need to print dates in a desired format.

Solution

Use the java.time.format.DateTimeFormatter class. It provides three types of formatters for printing date/time values:

This is an excerpt from the Scala Cookbook, 2nd Edition. This is Recipe 3.10, Calculating The Difference Between Two Dates.

Problem

While using Scala (2 or 3), you need to determine the difference between two dates.

Solution

If you need to determine the number of days between two dates, the DAYS enum constant of the java.time.temporal.ChronoUnit class is the easiest solution:

My 700+ page book, Functional Programming, Simplified — 4.5-star rated on Amazon, their 6th-best selling book on functional programming, and 5-star rated on Gumroad.com — is currently on sale in three formats (prices shown in USD):

I was having a problem connecting from a Google Cloud Run service to a Cloud SQL instance, so as part of the process of troubleshooting the problem I created the following Scala + MySQL + JDBC database test code. The idea was to create the code as simply as possible — with as few dependencies as possible — to try to understand the problem.

This is an excerpt from the Scala Cookbook, 2nd Edition. This is Recipe 23.7, Creating Meaningful Type Names with Opaque Types.

Problem

In keeping with practices like Domain-Driven Design (DDD), you want to give values that have simple types like String and Int more meaningful type names to make your code safer.

Solution

In Scala 3, use opaque types to create meaningful type names. For an example of the problem, when a customer orders something on an e-commerce website you may add it to a cart using the customerId and the productId:

This is an excerpt from the Scala Cookbook, 2nd Edition. This is Recipe 24.7, Building Modular Systems with Scala 3.

Problem

You’re familiar with Martin Odersky’s statement that Scala developers should use “functions for the logic, and objects for the modularity,” so you want to know how to build modules in Scala.

This is the beginning of a Docker cheat sheet. I couldn’t find any out here that I liked, so I’m starting to create my own, which will hopefully be organized the way I like it.

This content is cross-posted at My Valley Programming Docker cheat sheet.

Docker Basics

Recommended as a first command on a Docker system:

docker version     # should show Client and Server sections

Docker Lifecycle

This section mostly comes from (https://github.com/wsargent/docker-cheat-sheet):

As a quick blog post, these are some notes and steps I used to create a Scala JAR file, put that in a Docker image, and then push it up to Google Cloud Run. Rather than add a lot of description here, I’ll just share my notes in a numbered order.

Note that I have cross-posted this article on my Valley Programming website at Pushing a Scala JAR/Docker file to Google Cloud Run to create a service.

These are my notes from creating a Play Framework 2.8 project on January 2, 2022, using Scala 2.13, MySQL, and Slick. I share these notes here because I found it hard to find the correct versions of everything that needed to be used, and the correct syntax in the application.conf file. Unfortunately the Play 2.8 documentation is not up to date, so this was much harder than I expected it to be.

This is an excerpt from the Scala Cookbook, 2nd Edition. This is Recipe 20.3, Reading a CSV File Into a Spark RDD.

Problem

You want to read a CSV file into an Apache Spark RDD.

Solution

To read a well-formatted CSV file into an RDD:

This is an excerpt from the Scala Cookbook, 2nd Edition. This is Recipe 20.2, Reading a File Into an Apache Spark RDD.

Problem

You want to start reading data files into a Spark RDD.

Solution

The canonical example for showing how to read a data file into an RDD is a “word count” application, so not to disappoint, this recipe shows how to read the text of the Gettysburg Address by Abraham Lincoln, and find out how many times each word in the text is used.

After starting the Spark shell, the first step in the process is to read a file named Gettysburg-Address.txt using the textFile method of the SparkContext variable sc that was introduced in the previous recipe:

This is an excerpt from the Scala Cookbook, 2nd Edition. This is Recipe 20.1, Getting Started with Apache Spark.

Scala Problem

You’ve never used Spark before, and want to get started with it.

Solution

When you use Spark professionally, your data will probably be spread across multiple computers — maybe thousands of computers — but to get started with Spark you can do all of your work on one computer system in “local mode.” The easiest way to do this is to start the Spark shell, create an array, and go from there.

Back when I was writing Functional Programming, Simplified I started to write a little Scala/FP “To-Do List” application that you can run from the command line, based on a similar application in the Learn You A Haskell For Great Good book. For reasons I don’t remember, I decided not to include it in the book, and forgot about it until I started using GraalVM (“Graal”) recently.

This is an excerpt from the Scala Cookbook, 2nd Edition. This is Recipe 3.8, Formatting Numbers and Currency.

Scala 3 Problem

You want to format numbers or currency to control decimal places and separators (commas and decimals), typically for printed output.