Add MultiGetResponse::toString method

[NeilRickards]

c.f. SearchResponse::toString

[elasticmachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?

[cbuescher]

You can simply use Strings.toString(this) instead, at least that's what e.g. GetResponse does.

[cbuescher]

Sorry, this doesn't compile now.

[cbuescher]

@NeilRickards thanks for this PR. I left a comment about how I think this can be made shorter. More generally I'm wondering if we should go down the road of adding toString() methods to all kinds of ActionResponses. There are a few that already do this, but a majority that don't. It might be useful to do this in a more generic way, I don't know if we ever had this discussion but maybe other can comment.

[NeilRickards]

That's much neater - I've updated the PR.
I wonder if there's scope for making ActionResponse implement ToXContentObject and overriding toString at that level.

[cbuescher]

From the looks of it, not all ActionResponses implement ToXContent/ToXContentObject so this will be difficult I think.

[javanna]

See #3889 . Making ActionResponse implement ToXContentObject should be possible, yet it may require quite some work. We could do it as part of adding support for new apis to the REST high level client.

As for adding toString in general, I even wonder if the toString should output the json representation. Anyways, I am ok with this change. Shall we have a test somewhere?

[cbuescher]

@NeilRickards revisiting this after some time, whould you mind adding a short test for the toString() output like @javanna suggested?

[javanna]

I am closing this for now given that it's missing tests and we are not going to integrate it without them. Feel free to reopen once you have time to work on it. Thanks!