KAFKA-10403: Replace Scala collection by Java collection in Log4jController (#9182)

This removes the need to have the Scala library in the classpath
when deserializing the MBean.

Reviewers: Ismael Juma <ismael@juma.me.uk>

core/src/main/scala/kafka/utils/Log4jController.scala

@@ -87,9 +87,10 @@ object Log4jController {
 class Log4jController extends Log4jControllerMBean {
 
   def getLoggers: util.List[String] = {
-    Log4jController.loggers.map {
+    // we replace scala collection by java collection so mbean client is able to deserialize it without scala library.
+    new util.ArrayList[String](Log4jController.loggers.map {
       case (logger, level) => s"$logger=$level"
-    }.toList.asJava
+    }.toSeq.asJava)
   }
 
 

core/src/test/scala/kafka/utils/LoggingTest.scala

@@ -26,6 +26,14 @@ import org.junit.Assert.{assertEquals, assertTrue}
 
 class LoggingTest extends Logging {
 
+  @Test
+  def testTypeOfGetLoggers(): Unit = {
+    val log4jController = new Log4jController
+    // the return object of getLoggers must be a collection instance from java standard library.
+    // That enables mbean client to deserialize it without extra libraries.
+    assertEquals(classOf[java.util.ArrayList[String]], log4jController.getLoggers.getClass)
+  }
+
   @Test
   def testLog4jControllerIsRegistered(): Unit = {
     val mbs = ManagementFactory.getPlatformMBeanServer()