Fix StringEncoder javadoc Java version and Android condition

[thswlsqls]

Fixes #8709

Description

• The javadoc called UnsafeStringEncoder a "Java 8+" implementation, but createIfAvailable() needs the String.value (byte[]) and String.coder fields, which Java 8 does not have, so Java 8 always falls back. The inline comment on the coder lookup already says "this only exists in Java 9+".
• That wording came from VarHandle string encoder #7701 and was carried over unchanged when Fix StringEncoder javadoc implementation priority order #8621 reordered the same bullet.
• Separately, Avoid unsafe string encoder on Android #8637 added an Android (Dalvik) early return to createUnsafeEncoder(), but the bullet still listed only the Java version condition. Added it to the same sentence.
• Updated the matching wording in the UnsafeStringEncoder javadoc and the StringEncoderHolder log message.

Testing done

• Docs-only, test-exempt: javadoc and one non-asserted Level.FINE log message; no behavior or API change.
• ./gradlew :exporters:common:check passed — 70 tests (61 test, 8 testSenderProvider, 1 testWithoutUnsafe), 0 failures.
• No apidiff update: all touched classes are japicmp-excluded io.opentelemetry.exporter.internal.*.

[opentelemetry-pr-dashboard]

Pull request dashboard status

Waiting on the author · refreshed 2026-08-14 16:27 UTC

Respond to 1 review item (e.g. link a commit, explain why not, ask a follow-up):

• Inline threads: 1

Status above doesn't look right?

• Just replied or pushed? Anything around or after the refresh time above may not be picked up yet — give it a few minutes.
• Should this be with reviewers? Comment /dashboard route:reviewers to route it to them.
• Anything wrong — including the routing? Report it with what you expected; it helps us improve the dashboard.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 91.65%. Comparing base (d948e13) to head (37dac01).

Files with missing lines	Patch %	Lines
...exporter/internal/marshal/StringEncoderHolder.java	0.00%	1 Missing ⚠️

❌ Your patch check has failed because the patch coverage (0.00%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #8711   +/-   ##
=========================================
  Coverage     91.65%   91.65%           
  Complexity    10352    10352           
=========================================
  Files          1003     1003           
  Lines         27210    27210           
  Branches       3199     3199           
=========================================
  Hits          24939    24939           
  Misses         1566     1566           
  Partials        705      705           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[jack-berg]

But the UnsafeStringEncoder is java 8+ 🤔

[thswlsqls]

@jack-berg Thanks for the review. This encoder is never selected on Java 8: createIfAvailable() requires String.value to be a byte[] and String.coder to exist, both compact-strings fields, and Java 8's String.value is a char[] — so it returns null. The existing comment on the coder lookup says the same thing.

You're right that the class itself compiles for Java 8; the doc sentence is about which runtimes actually get it. Happy to word it that way instead.

[jack-berg]

After looking closer, you are correct, and this indeed is reflected in unit tests: https://github.com/open-telemetry/opentelemetry-java/blob/main/exporters/common/src/test/java/io/opentelemetry/exporter/internal/marshal/StringEncoderTest.java#L38

cc @trask