Serializing/deserializing dot-separated property keys as nested objects

[Martin Ellis]

Hello,

I was looking into the possibility of serializing/deserializing a Map<String, String> with dot-separated keys into a JSON structure.

I mention 'dot-separated keys' because I'd like the dots to denote nested objects in the JSON tree.

I wondered if there's already an implementation of this?

To clarify, I'd like the map:

    a.b=1

    a.c=2

    a.d.e=3

to be deserialised as:

{

    "a": {

        "b": 1,

        "c": 2,

        "d": {

            "e": 3

        }

    }

}

Error checking aside, I've put some draft code here:

  https://gist.github.com/martiell/e677c142518038f35379

Does anyone know if this has already been done?

Thanks

Martin

[Ian Barfield]

That syntax is a subset of hocon (which is a super set of json). Naturally, I'm partial to my own mash up at https://github.com/addthis/codec. However, there is another jackson-hocon module that has since changed its license from lgpl? to apache.

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[Martin Ellis]

Thanks, Ian. I wasn't aware of hocon. Looks like a good format for configuration files.

My use case is also for application configuration, although I was also thinking about environment variables with underscore-separated names (in addition to dot-separated property keys).

I think I'll continue to experiment with the module I posted for now, and merging it with a JSON tree from a config file (which means it'd be straight-forward to switch from YAML config to hocon later…)

Cheers,

Martin

[Tatu Saloranta]

Not sure if this is relevant, but I think this is what DropWizard does, to allow weaving in overrides from system properties into its main Configuration object.

The way DW does this is by first reading yaml/json content in a JsonNode tree, and then splitting dot-names into path, and adding/overriding nodes as necessary.

Code is not modular (I think), but as far as I remember it is relatively small chunk of code and possibly repurposable via cut'n pasting.

-+ Tatu +-

[Martin Ellis]

Hi Tatu,

Yes, very relevant, thanks.

I hadn't looked at the DropWizard implementation because the
documentation suggests that configuration using environment variables
(not system properties) isn't so elegant: to use an environment
variable override you need something in the configuration YAML like:

defaultSetting: ${DW_DEFAULT_SETTING:-default value}

… according to this:
https://dropwizard.github.io/dropwizard/manual/core.html#environment-variables

I didn't realise that system properties could be used in the way I described.

Here's the magic:

https://github.com/dropwizard/dropwizard/blob/master/dropwizard-configuration/src/main/java/io/dropwizard/configuration/ConfigurationFactory.java#L183

Cheers,
Martin

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