Serialize requests to json

[Tamir-Schwarz]

link to issue
#588

actually used the code of @dblock - thank you very much!

original example
https://github.com/dblock/opensearch-java-client-demo/blob/to-json/src/main/java/Example.java#L34

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[dblock]

I think with some documentation in USER_GUIDE or related this could be good enough.

[dblock]

Get rid of print outs.

[VachaShah]

I think with some documentation in USER_GUIDE or related this could be good enough.

+1. Some documentation on how to use toJson() for a class would be great!

[dblock]

@Tamir-Schwarz Want to finish this?

[Jai2305]

Hi @Tamir-Schwarz and @dblock , first of thanks for the contribution, all services of my organization are migrating from the High Level Rest Client to Java Client and very much like these kind of enhancements to be implemented, as they provide a clean code convenience to new clients.
Although I have some suggestions and I would like your opinion on them -

• Can we not implement this method in JsonpSerializable interface as a default method, I think it will be a better design as it will ensure that only classes implementing the interface are allowed to utilize the default method, you could internally call serialize method of the interface, this will avoid implementation and call to a utils class.
• Also you can try implementing JsonGenerator generator = mapper.jsonProvider().createGenerator(stringWriter); with try with resource block to ensure that the generator is closed automatically even if an exception occurs.
• Finally please include test cases for classes which are implementing JsonpSerializable indirectly, just to ensure the robustness of code , for eg. IndexResponse extends WriteResponseBase implements JsonpSerializable .

[dblock]

@Jai2305 These look very reasonable. Want to open another PR with your suggestions?

[Jai2305]

@dblock thanks for a quick response, I am on it.

[Xtansia]

A version of this utility was added via #588, documented here: https://github.com/opensearch-project/opensearch-java/blob/main/guides/json.md#using-tojsonstring