Micrometer metrics tags extension

[Kuvaldis]

Following Micrometer features added:

1. Add timer metrics to requests resulting with exception. E.g. in MeteredClient. Includes exception name as tag.
2. Add uri as default tag in MeteredClient metrics.
3. Support adding custom tags in metered client, encoder, decoder etc.

Fixes #1301

[kdavisk6]

@Kuvaldis looks like I may have merged your pull requests out of order. Can you check this one?

[Kuvaldis]

@kdavisk6 All done.

[kdavisk6]

@Kuvaldis

This looks OK to me. I'd like @velo to weigh in also. I'll mark it ready and allow for some additional comments before we merge.

[velo]

Overall, I think is a good improvement.

Things I would like to see
a) Not sure if make sense or no, but finally added to all try/catch blocks.
b) use Tag[] or Tags instead of List<Tag> + toArray(new Tag[] {}) combo
c) move metric naming to MetricName giving people one place for all customization needs.

[velo]

it would be nice not to change import ordering... but, don't worry too much about it =)

[velo]

I assume you are using this for some internal metrics (I would be curious to know what you are going =] )

I would prefer to see code to live in the MetricName interface... that would give a single place for all your tag customization needs.

We would have a few methods, one called requestExtraTags other one responseExtraTags, another like exceptionExtraTags

What do you think?

[Kuvaldis]

I extracted tags resolution to a separate extendable class. However, seems like depending on where we create tags (i.e. client, encoder/decoder, method handler) we have really different parameters to build tags upon. I added defaultTags method, which might be helpful for customization in general.

[Kuvaldis]

c) move metric naming to MetricName giving people one place for all customization needs.

Basically, there is String name(String suffix) should be enough, depending on suffix it can be overriden, for example. Another option is to create a separate method for each metric, but I think it is too specific and not really required.

[r1jsheth]

is there any example depicting this use case?