Try using classutil to find Spark classes.

dev/mima

@@ -39,7 +39,7 @@ generate_mima_ignore() {
     java \
       -XX:MaxPermSize=1g \
       -Xmx2g \
-      -cp "$1:$TOOLS_CLASSPATH" \
+      -cp "$TOOLS_CLASSPATH:$1" \
       org.apache.spark.tools.GenerateMIMAIgnore
 }
 

tools/pom.xml

@@ -42,6 +42,11 @@
       <groupId>org.scala-lang</groupId>
       <artifactId>scala-compiler</artifactId>
     </dependency>
+    <dependency>
+      <groupId>org.clapper</groupId>
+      <artifactId>classutil_${scala.binary.version}</artifactId>
+      <version>1.0.6</version>
+    </dependency>
   </dependencies>
 
   <build>

tools/src/main/scala/org/apache/spark/tools/GenerateMIMAIgnore.scala

@@ -18,15 +18,13 @@
 // scalastyle:off classforname
 package org.apache.spark.tools
 
-import java.io.File
-import java.util.jar.JarFile
-
 import scala.collection.mutable
-import scala.collection.JavaConverters._
 import scala.reflect.runtime.{universe => unv}
 import scala.reflect.runtime.universe.runtimeMirror
 import scala.util.Try
 
+import org.clapper.classutil.ClassFinder
+
 /**
  * A tool for generating classes to be excluded during binary checking with MIMA. It is expected
  * that this tool is run with ./spark-class.
@@ -161,35 +159,13 @@ object GenerateMIMAIgnore {
    * and subpackages both from directories and jars present on the classpath.
    */
   private def getClasses(packageName: String): Set[String] = {
-    val path = packageName.replace('.', '/')
-    val resources = classLoader.getResources(path)
-
-    val jars = resources.asScala.filter(_.getProtocol == "jar")
-      .map(_.getFile.split(":")(1).split("!")(0)).toSeq
-
-    jars.flatMap(getClassesFromJar(_, path))
-      .map(_.getName)
-      .filterNot(shouldExclude).toSet
-  }
-
-  /**
-   * Get all classes in a package from a jar file.
-   */
-  private def getClassesFromJar(jarPath: String, packageName: String) = {
-    import scala.collection.mutable
-    val jar = new JarFile(new File(jarPath))
-    val enums = jar.entries().asScala.map(_.getName).filter(_.startsWith(packageName))
-    val classes = mutable.HashSet[Class[_]]()
-    for (entry <- enums if entry.endsWith(".class")) {
-      try {
-        classes += Class.forName(entry.replace('/', '.').stripSuffix(".class"), false, classLoader)
-      } catch {
-        // scalastyle:off println
-        case _: Throwable => println("Unable to load:" + entry)
-        // scalastyle:on println
-      }
-    }
-    classes
+    val finder = ClassFinder()
+    finder
+      .getClasses
+      .map(_.name)
+      .filter(_.startsWith(packageName))
+      .filterNot(shouldExclude)
+      .toSet
   }
 }
 // scalastyle:on classforname