Better Java version parsing

Co-authored-by: David Gregory <[email protected]>

Author: armanbilge

settings/src/main/scala/org/typelevel/sbt/TypelevelSettingsPlugin.scala

@@ -278,9 +278,9 @@ object TypelevelSettingsPlugin extends AutoPlugin {
     jdkRelease.fold(default) {
       case 8 if isJava8 => default
       case n if n >= 8 =>
-        if (javaRuntimeVersion < n) {
+        if (javaMajorVersion < n) {
           sys.error(
-            s"Target JDK is $n but you are using an older JDK $javaRuntimeVersion. Please switch to JDK >= $n.")
+            s"Target JDK is $n but you are using an older JDK $javaMajorVersion. Please switch to JDK >= $n.")
         } else {
           f(n)
         }
@@ -289,17 +289,14 @@ object TypelevelSettingsPlugin extends AutoPlugin {
           s"Target JDK is $n, which is not supported by `sbt-typelevel`. Please select a JDK >= 8.")
     }
 
-  private val javaRuntimeVersion: Int =
-    System.getProperty("java.version").split("""\.""") match {
-      case Array("1", "8", _*) => 8
-      case Array(feature, _*) => feature.toInt
-    }
+  private val javaMajorVersion: Int =
+    System.getProperty("java.version").stripPrefix("1.").takeWhile(_.isDigit).toInt
 
-  private val isJava8: Boolean = javaRuntimeVersion == 8
+  private val isJava8: Boolean = javaMajorVersion == 8
 
   private val javaApiMappings = {
     // scaladoc doesn't support this automatically before 2.13
-    val baseUrl = javaRuntimeVersion match {
+    val baseUrl = javaMajorVersion match {
       case v if v < 11 => url(s"https://docs.oracle.com/javase/${v}/docs/api/")
       case v => url(s"https://docs.oracle.com/en/java/javase/${v}/docs/api/java.base/")
     }