Provide a log writer to produce JSON log items according to Elastic Common Schema

[hlemcke]

In addition to "log(String, ...)" provide something like "logJson(Map<String,Object>)" and a class with predefined keys from Elastic Common Schema.

It would make sense to also provide an option to set some predefined keys to Floggerwhich will be used (merged) by method "logJson()" when writing the log entry. (keys like application name and current version)

[chaoren]

You can use a MetadataKey for this, no? logJson seems like an unnecessary addition that goes against the fluent design of the flogger API.

[hlemcke]

The fluent Api is and should stay as a basic design rule. Json logging would only be an addition. I would appreciate to have two methods like:

• withData(Map<String,Object> jsonMap) to set data used in all following log entries from this logger
• logJson(String message, Map<String,Object> jsonMap) to log entries according to Elastic Common Schema

[chaoren]

The fluent design is kind of the whole point of Flogger. It's even in the name! It's repeated several times throughout https://google.github.io/flogger/anatomy that this is a very intentional design choice.

For example https://google.github.io/flogger/anatomy#fluent-api

Flogger’s API is designed to require only a single conceptual log method in its API.

If we are to add logJson for this "Elastic Common Schema," then we'd be expected to add a different log method for all the different schemas out there. We'd end up with log, logJson, logXml, logCsv, etc, for every data format imaginable. A single log method plus whatever configuration you want in the fluent chain leading up to it already provides everything necessary to achieve what you're asking for. There is absolutely zero need for a separate log method.

[chaoren]

You could just write a flogger extension so instead of needing logJson(String message, Map<String,Object> jsonMap), you can just do withJson(Map<String,Object> jsonMap).log(String message). Please see https://google.github.io/flogger/anatomy for why we don't want logJson to be a single method.

[hlemcke]

Hi charoren. Thanks for still helping me out. It definitiely feels best to go with something like withJson(Map<String,Object> jsonMap).log(String message)! Do you have any hint where I can find some examples how to implement this?

[chaoren]

You can find some good answers by searching for this on the internet:

• https://stackoverflow.com/questions/56262887/how-does-one-extend-the-flogger-fluent-api-for-domain-specific-attributes
• https://groups.google.com/g/flogger-discuss/c/J1pM68LpVvA/m/Y3pmcld-BQAJ

You could also ask directly on https://stackoverflow.com/ if those answers are not sufficient.

[hlemcke]

That helps. Thank you very much!

[hagbard]

See my new site dedicated to providing better Flogger documentation: https://hagbard.github.io/the-flogger-manual/advanced/#metadata-contexts-and-scopes

You can implement passing the data without need for a new API method by using a suitably named metadata key:

private static final MetadataKey<MyJsonMapType> JSON_MAP = MetadataKey.single("json_map", MyJsonMapType.class);

logger.atWarning().with(JSON_MAP, map).log(...);

Passing structured or semi-structured data is exactly what metadata is for.

Also, if you want the same values passed to lots of log statements, use ScopedLoggingContexts rather than passing values in. This also gives you access to Tags, which might be just what you want.

HOWEVER, what the logger backend does with this is a different issue. What do you actually want the output to be (you might need a new backend or a customized MetadataKey) ?