modernize jdk level and dependencies

[sreuland]

What problem does your feature solve?

jdk is pinned to LTS 1.8 from 2014 version.
uses some library deps that were prior required due to gaps in older jdk's such as threeten for date/time and to some degree google guava and okhttpclient.

What would you like to see?

upgrade the jdk to LTS 11 which came out in 2018.

evaluate using builtin java.net.HTTPClient and removing dep on okhttpclient which pulls in entire Kotlin library for not much value-add

• use as opportunity for refactor to streamline org.stellar.sdk.Server, don't expose internal http client aspect
  • replace current constructors with a org.stellar.sdk.ServerBuilder with required param setterwithServerURL, and optionals forwithTimeout, withTxSubmitTimeout
  • remove getter/setters for internal http client

use jdk built-in java.time.* instead of threeten dep

What alternatives are there?

[Ifropc]

FYI: removing deps on okhttpclient will break existing users who provide their own instance of okhttpclient in order to customize client (i.e. timeouts, etc)

[sreuland]

FYI: removing deps on okhttpclient will break existing users who provide their own instance of okhttpclient in order to customize client (i.e. timeouts, etc)

yes, thanks for pointing out, would be breaking change for org.stellar.sdk.Server since it exposes the http client internals like that with constructors and getter/setters. I updated details on description to include that scope for consideration.

[overcat]

Can we consider removing the guava dependency? After upgrading to version 1.8+, most of the functionalities we use in guava have alternatives in the standard library, except for ImmutableList, but is it worth introducing it just for ImmutableList?

[sreuland]

Can we consider removing the guava dependency? After upgrading to version 1.8+, most of the functionalities we use in guava have alternatives in the standard library, except for ImmutableList, but is it worth introducing it just for ImmutableList?

yes, I think your current pr could be one place to try or we create another tech debt ticket specific to guava removal as it touches alot of files.

https://github.com/stellar/java-stellar-sdk/pull/523/files/2555cfebc54ac8428d4c3319902929ebf7277356..2d0561a5f7f1df27386b1dbb0fcf640235d6c449

[overcat]

Currently, java.net.HTTPClient cannot be used on the Android platform(source). Of course, we can design the http client as an interface and provide services through java.net.HTTPClient in this SDK, and then use OkHttpClient to provide services on the Android platform through SPI.