Posted under Spring & Spring Boot
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Tags Spring, SpringBoot
I was using @Configuration on a configuration class in order to load its properties from application.properties.
This is detailed in this post here.
As per the post, Spring Boot supports lists and maps in the way you would expect, and handles nested objects including Collections such as maps and lists.
It can therefore handle a complete object graph of configuration properties in a clean manner, and also happily supports generics too.
Map keys can be specified either using the “.key” syntax, or the bracketed [key] syntax (which is also used with numeric values to create lists).
The problem I hit was that a map property group, used to create mock response objects keyed on a token string, was being completely ignored even though correctly specified in application.properties.
There were no errors or messages about this the log, even when debug logging was turned on – Spring appeared to be just ignoring the properties completely.
After some significant head banging the problem was trivial.
I was using Lombok to eliminate boiler plate, and both the map class and its descendants had Lombok @AllArgsContructors and static factory methods for my own object creation.
However this meant that they did not have a no args constructor as I had not specified one. I did not need one, but Spring Boot absolutely relies on this to work!
Once I created the required constructor via @NoArgsConstructor, everything worked fine.
Hats off to Spring for this excellent way to manage config as a nice object graph, but it would be useful to have some kind of warning when a target class does not have a no args constructor!
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