Downgrade client to build with Java 8

[harshavamsi]

Description

Coming from #156, this downgrades the target to Java 8. This has to go in after #326.

Issues Resolved

Closes #156

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[dlvenable]

Nice! Thanks @harshavamsi !

Ideally, this project should also include the Java 8 in the build/test Java version matrix.

opensearch-java/.github/workflows/build.yml

Lines 8 to 10 in a924a74

	strategy:
	matrix:
	java: [ 11 ]

I think ideally all the tests would run on Java 8 and 11. But, some of the integration tests require Java 11 due to the OpenSearch test framework. Maybe the project could run the build and unit tests on Java 8/11. And then run only integration tests on Java 11.

[reta]

Nice! Thanks @harshavamsi !

Ideally, this project should also include the Java 8 in the build/test Java version matrix.

opensearch-java/.github/workflows/build.yml

Lines 8 to 10 in a924a74

	strategy:
	matrix:
	java: [ 11 ]

I think ideally all the tests would run on Java 8 and 11. But, some of the integration tests require Java 11 due to the OpenSearch test framework. Maybe the project could run the build and unit tests on Java 8/11. And then run only integration tests on Java 11.

@dlvenable we cannot do that now, the opensearch-java uses test-framework from core - this is still JDK-11, so we either drop this dependency (copy tons of stuff) or use JDK-11+ for compile / build / test

[dlvenable]

Nice! Thanks @harshavamsi !
Ideally, this project should also include the Java 8 in the build/test Java version matrix.

opensearch-java/.github/workflows/build.yml

Lines 8 to 10 in a924a74

	strategy:
	matrix:
	java: [ 11 ]

I think ideally all the tests would run on Java 8 and 11. But, some of the integration tests require Java 11 due to the OpenSearch test framework. Maybe the project could run the build and unit tests on Java 8/11. And then run only integration tests on Java 11.

@dlvenable we cannot do that now, the opensearch-java uses test-framework from core - this is still JDK-11, so we either drop this dependency (copy tons of stuff) or use JDK-11+ for compile / build / test

This is probably beyond the scope of this PR, but we may wish to split the integration tests (which use the test-framework) from unit tests.

[dblock]

If we can run some basic tests with JDK8 I'd be satisfied. We can then run the full suite with JDK11 and have more work items about increasing test coverage on JDK8 by moving frameworks. Hope you can finish this @harshavamsi!

[rgopidiaws]

can you please prioritize this? we are currently blocked on this as we have a service which is using JDK8 and we are not able to use this client in that service. Appreciate it if you can prioritize this.

[dblock]

@rgopidiaws This hasn't been touched for a while so I am afraid nobody is working on this right now. Want to give it a try?

[dblock]

@harshavamsi Any interest in re-picking this up on your copious free time (TM)? :)

[VachaShah]

Closing this PR since restoring support for Java 8 is done.