I was querying a Postgres table with about 4 million rows and writing some of the fields to a CSV. I knew loading the rows into RAM was unacceptable, so I used the MyBatis class ResultHandler to process the records. The code ran fine locally, but in production we were having memory usage issues.

I was writing a WSDL-first SOAP 1.1 service (server) using Apache CXF. I needed to directly access the XML DOM of the SOAP Header and Body, so I did not want to use the standard JAXB data binding. My solution was to implement a Provider using message mode. However, retrieving the SOAPAction inside the Provider’s invoke(SOAPMessage msg) method was not intuitive to me.

I prefer to not run web applications as root. authbind allows you to run the application as a user other than root, but bind to ports 80 and 443.

Creating a Java-based service on Linux that will start when the operating system boots and run continuously doesn’t require any extra libraries, despite many internet posts to the contrary.

Be wary of loops in automated (JUnit) tests. I have written automated tests that didn’t actually verify anything because the body of the loop was never executed.

FreeMarker formatted an integer with a comma when I didn’t expect it. This caused my form post to fail.

Question I was asked today, which I thought was simple: “How do I convert a java.time.Instant to UTC?”

To write an application that works, you must handle unexpected conditions.

A Java server I wrote was storing date/time values in MySQL incorrectly during the transition from Daylight Saving Time to Standard Time. The solution was to force MySQL to store everything in Coordinated Universal Time (UTC).

If you persistently store an instant in time (aka a timestamp), then that instant must be stored in Coordinated Universal Time (UTC)^*.