Inconsistency between binder property paths

[copitz]

TL;DR:
The keys of nested properties bound to a Map<String, String> look like "foo.0.bar" but should be "foo[0].bar".

Further explanation:
This one took me hours to figure out and I managed to work around it by replacing all "\\.([0-9]+)(\\.|$)"with [$1]$2 in the keys of the map - anyway I think that it could help someone stumbling upon this and especially when it could be fixed:

To enable polymorph configuration property bindings (and also retrieve such bindings from other sources like a database or webservice) I let spring boot bind (nested) properties under a certain path to a Map<String, String> and use this as MapConfigurationPropertySource for the new Binder API to bind them to the concrete classes.

This worked fine until I stumbled upon collections/arrays leading to weired behaviors of the binder (e.g. keeping dots in the property path). After a while I found out that this was caused by the wrong form of the property paths.

Please let me know if I should add some code / test case to make this clearer.

[mbhave]

@copitz I'm not sure I fully understood the issue. A minimal sample that showcases the issue or a test case would be very useful.

[copitz]

@mbhave Sure, hope this helps: https://github.com/copitz/spring-boot-issue-17615

[mbhave]

Thanks for the sample @copitz. I took a look and this is the expected behavior:

When ApplicationBinderTest runs, the first binding that occurs is binding properties under the acme prefix to ExampleProperties. Properties are bound to a Map<String, Map<String, String>>. When the binder binds properties to a Map, it removes everything that is not an alpha-numeric character. In this case, [ and ] get removed and the values in the Map end up being entity-filters.products.0.pattern and entity-filters.products.0.include. This is documented here

When binding to Map properties, if the key contains anything other than lowercase alpha-numeric characters or -, you need to use the bracket notation so that the original value is preserved. If the key is not surrounded by [], any characters that are not alpha-numeric or - are removed.

This is why it works when you add the [ ] for the second test.

When you use Spring Boot's @ConfigurationProperties to bind directly to StoreApplication, it has the key in the original form (since you are directly binding keys under acme.applications.foo ).

One way to avoid manually fixing the property names would be to specify the properties using the convention mentioned in the docs linked above. Using acme.applications.foo.[entity-filters.products[0].pattern] would work as the original [0] would be preserved.

We have an open issue #13404 for investigating if map keys can preserve their original value without having to surround them with [ ]. I'll close this one in favor of that.

[copitz]

Thank you @mbhave for the clarification