feat: streaming example

[kwasniew]

About the changes

Now that we released a new version of Java SDK with streaming support we can also add an example.

Run it with UNLEASH_API_TOKEN=sandbox_token UNLEASH_API_URL=sandbox_url ./gradlew run

The example listens to streaming changes and prints flag status and received events.

Most of the PR is boilerplate for gradle copied from other examples. Actual change is 60 LOC

Important files

Discussion points

[kwasniew]

version with streaming required

[kwasniew]

optional dependency for streaming

[coveralls]

Pull Request Test Coverage Report for Build 17093964056

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 79.249%

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Totals
Change from base Build 16902971413:	0.0%
Covered Lines:	2442
Relevant Lines:	3010

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💛 - Coveralls

[gastonfournier]

I manually tested it against a server without streaming support, and it doesn't fall back to polling. I don't know if it's the intended behavior but it does use the backup to load the initial state but it does not fetch from upstream.

I double-checked, and it's not polling. I believe it should poll if streaming fails.

[gastonfournier]

Against a server that supports streaming:

1. If streaming is disabled from the client it works well with polling.
2. If experimental mode streaming is disabled you can still have a streaming listener that will report (odd but not terrible)
3. With experimental mode streaming enabled it works nicely.

The main difference with a server that doesn't support streaming is that the client will output:

[STREAMING ERROR] Streaming connection error

Which probably means the error is not handled (because disabling streaming works).

[gastonfournier]

This looks good! The happy path works well. We know about this limitation #322 (comment) but it will be addressed later. Meanwhile, the features is clearly marked as experimental which means, it should not be used in production yet. Good step forward!

[gastonfournier]

Looks ok, I'd like to also get some feature evaluation result, but I tested that manually and it works well.

I did something similar to this:

unleash-java-sdk/examples/cli-example/src/main/java/io/getunleash/example/AdvancedConstraints.java

Lines 29 to 32 in 41c6028

	while (true) {
	unleash.isEnabled("advanced.constraints", context); // expect this to be true
	unleash.isEnabled("advanced.constraints", smallerSemver); // expect this to be false
	}

but limiting to 100 iterations with a sleep.

[kwasniew]

There's boolean isEnabled = unleash.isEnabled("streaming_flag"); which is a flag you need to create and you will see it changing instantly on every streaming change. This is a similar pattern I did in Node SDK where we react to instant changes instead of looping which was fine for the polling mindset but for streaming event listening mindset seems to be more appropriate for me.