What are alternatives to DateTimeFormatter i18n and how do they compare?

DateTimeFormatter is a powerful tool in Java for formatting and parsing date-time objects. However, there are several alternatives which can be beneficial depending on the use case. Below, we outline some of these alternatives and how they compare to DateTimeFormatter.

1. SimpleDateFormat: This is a legacy class from Java 1.1 that allows for formatting and parsing dates. It's not thread-safe, which can lead to issues in multi-threaded environments. In contrast, DateTimeFormatter is thread-safe and generally preferred in modern applications.

2. Joda-Time: Before Java 8 introduced the `java.time` package, developers often used Joda-Time for date and time manipulation. Joda-Time is still a solid alternative, offering a rich set of functionality, but it is considered less modern compared to Java's built-in `java.time` APIs.

3. Apache Commons Lang DateUtils: This utility class offers helper methods for working with dates, but it's more focused on date comparisons, manipulation, and formatting in a simplified manner, rather than extensive formatting options like DateTimeFormatter.

4. Third-party libraries (e.g., THREETEN-BP, Time4J): These libraries provide additional features that might not be available in the standard Java libraries, focusing on time zones and complex date-time arithmetic.

In summary, while DateTimeFormatter is powerful and thread-safe, alternatives like SimpleDateFormat, Joda-Time, and others can be useful based on specific requirements, especially for older legacy systems or when needing additional features.