24 hour time format: Difference between JodaTime and java.time

We have been using JodaTime in many projects since before Java got better date and time support with Java 8. We update projects to the newer java.time classes whenever we work on them, but some still use JodaTime. One of these was a utility that imports time series from CSV files. The format for the time stamps is flexible and the user can configure it with a format string like “yyyyMMdd HHmmss”. Recently a user tried to import time series with timestamps like this:

As you can see this is a 24-hour format. However, the first hour of the day is represented as the 24th hour of the previous day if the minutes and seconds are zero, and it is represented as “00” otherwise. When the user tried to import this with the “yyyyMMdd HHmmss” format the application failed with an internal exception:

org.joda.time.IllegalFieldValueException:
Cannot parse "20200101 240000": Value 24 for
hourOfDay must be in the range [0,23]

Then he tried “yyyyMMdd kkmmss”, which uses the “kk” format for hours. This format allows the string “24” as hour. But now “20200101 240000” was parsed as 2020-01-01T00:00:00 and not as 2020-01-02T00:00:00, as intended.

I tried to help and find a format string that supported this mixed 24-hour format, but I did not find one, at least not for JodaTime. However, I found out that with java.time the import would work with the “yyyyMMdd HHmmss” format, even though the documentation for “H” simply says “hour-of-day (0-23)”, without mentioning 24.

The import tool was finally updated to java.time and the user was able to import the time series file.