ThreadFactoryProvider.getJavaVersion() mis-parses bare major version strings (e.g. "21", "22")

[mvallim]

Bug

ThreadFactoryProvider.getJavaVersion() incorrectly parses java.version when the value has no dot and no dash — which happens for bare major-version strings such as "21" or "22" (a legitimate value of java.version, e.g. right at a JDK major GA release before the first patch update).

Current code (amazon-sns-java-messaging-lib-template/src/main/java/com/amazon/sns/messaging/lib/concurrent/ThreadFactoryProvider.java):

final int dotPos = version.indexOf('.');
final int dashPos = version.indexOf('-');
final int endIndex = dotPos > -1 ? dotPos : dashPos > -1 ? dashPos : 1;

return Integer.parseInt(version.substring(0, endIndex));

When neither a dot nor a dash is present, endIndex falls back to the literal 1,
so only the first character of the version string is parsed.

Reproduction

System.out.println(getJavaVersion("21"));   // expected 21, actual 2
System.out.println(getJavaVersion("22"));   // expected 22, actual 2
System.out.println(getJavaVersion("21.0.1")); // 21, correct (has a dot)

Impact

getJavaVersion() >= 21 gates whether ThreadFactoryProvider uses the virtual-thread factory (Java 21+) or falls back to Executors.defaultThreadFactory(). On a JVM whose java.version is a bare "21" or "22" (no . or - suffix), the check silently
resolves to false, so the library falls back to platform threads instead of virtual threads — with no error or exception, just a slightly misleading log line ("Java version is 2, using default thread factory").

Fix

Use version.length() instead of the literal 1 as the fallback end index, so the whole remaining string is parsed when there's no dot or dash:

final int endIndex = dotPos > -1 ? dotPos : dashPos > -1 ? dashPos : version.length();

Verification

input	before	after (fixed)
"21"	2	21
"22"	2	22
"21.0.1"	21	21
"17.0.9"	17	17
"1.8.0_302"	8	8
"11-ea"	11	11
"9"	9	9