Upgrade guava version to support higher JDK version

[kezhenxu94]

Please answer these questions before submitting pull request

• Why submit this pull request?

• Bug fix

• New feature provided

• Improve performance

• Related issues

#3540 and #3477

skywalking/oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/annotation/AnnotationScan.java

Lines 54 to 56 in 5b039e9

	ClassPath classpath = ClassPath.from(this.getClass().getClassLoader());
	ImmutableSet<ClassPath.ClassInfo> classes = classpath.getTopLevelClassesRecursive("org.apache.skywalking");
	for (ClassPath.ClassInfo classInfo : classes) {

the classpath.getTopLevelClassesRecursive("org.apache.skywalking") returns empty set under JDK 8+, and it turns out to be an issue of Guava, see google/guava#3249 (comment) , this patch upgrades the Guava version to 23.1, and I've verified locally the exception disappear and OAP starts successfully

[wu-sheng]

Are you sure this could make oap running 9 and 9+?

And license needs to be upgraded. Why CI check didn't find version change?

[wu-sheng]

Maybe CI found the issue.

[kezhenxu94]

I've replayed the e2e tests under JDK 1.9 manually (which won't report check status back to this PR), let's wait and see the result, if it passes, I think it should generally work on 1.9 and above, https://builds.apache.org/job/skywalking-e2e-2/763/console

[wu-sheng]

If you see it passed, reply me here. I am using phone only, today.

[kezhenxu94]

@wu-sheng it passes under JDK 9, see the selected/highlighted words below the screenshot

[wu-sheng]

Cool. How about higher? 11 for example? I am thinking about we need JRE documentation update.

[kezhenxu94]

Cool. How about higher? 11 for example? I am thinking about we need JRE documentation update.

I tested this afternoon locally with OpenJDK 12, it works fine too, so it's highly possible that it also works on JDK 10 and JDK11, do we need to replay this on the infra Jenkins?

[wu-sheng]

The infra is setting up our VM. Please submit an issue to track the higher jdk tests.

In this PR, at least, we should update document.

[kezhenxu94]

Oops, I've made a mistake that the container in which our e2e runs is based on OpenJDK8, the JDK version in Jenkinsfile-E2E is just for compile time only, so we'll need some real tests

[wu-sheng]

OK, so we haven't verified in 9+?

[kezhenxu94]

OK, so we haven't verified in 9+?

I verified JDK12 locally, others are not verified yet

[kezhenxu94]

We may need much more resources if we want to verify every commit on those versions

[wu-sheng]

OK. I think 9 and 11 are LTS versions, right? We could focus on that.

[wu-sheng]

/run ci