[GLUTEN-8462][CH] Fixed the loading of Components and Backend

gluten-core/src/main/java/org/apache/gluten/utils/ResourceUtil.java

@@ -47,12 +47,24 @@ public class ResourceUtil {
    */
   public static List<String> getResources(final Pattern pattern) {
     final List<String> buffer = new ArrayList<>();
-    final String classPath = System.getProperty("java.class.path");
+    String classPath = System.getProperty("java.class.path");
+    processClassPathElements(classPath, pattern, buffer);
+    if (buffer.isEmpty()) {
+      classPath = ResourceUtil.class.getProtectionDomain().getCodeSource().getLocation().getPath();
+      processClassPathElements(classPath, pattern, buffer);
+    }
+    return Collections.unmodifiableList(buffer);
+  }
+
+  private static void processClassPathElements(
+      String classPath, Pattern pattern, List<String> buffer) {
+    if (classPath == null || classPath.isEmpty()) {
+      return;
+    }
     final String[] classPathElements = classPath.split(File.pathSeparator);
     for (final String element : classPathElements) {
       getResources(element, pattern, buffer);
     }
-    return Collections.unmodifiableList(buffer);
   }
 
   private static void getResources(

gluten-core/src/main/scala/org/apache/gluten/GlutenPlugin.scala

@@ -95,6 +95,7 @@ private[gluten] class GlutenDriverPlugin extends DriverPlugin with Logging {
     val glutenBuildInfo = new mutable.LinkedHashMap[String, String]()
 
     val components = Component.sorted()
+    assert(components.nonEmpty)
     glutenBuildInfo.put("Components", components.map(_.buildInfo().name).mkString(", "))
     components.foreach {
       comp =>
@@ -269,7 +270,9 @@ private[gluten] class GlutenExecutorPlugin extends ExecutorPlugin {
   /** Initialize the executor plugin. */
   override def init(ctx: PluginContext, extraConf: util.Map[String, String]): Unit = {
     // Initialize Backend.
-    Component.sorted().foreach(_.onExecutorStart(ctx))
+    val components = Component.sorted()
+    assert(components.nonEmpty)
+    components.foreach(_.onExecutorStart(ctx))
   }
 
   /** Clean up and terminate this plugin. For example: close the native engine. */

gluten-core/src/test/scala/org/apache/gluten/component/ComponentSuite.scala

@@ -17,6 +17,7 @@
 package org.apache.gluten.component
 
 import org.apache.gluten.backend.Backend
+import org.apache.gluten.exception.GlutenException
 import org.apache.gluten.extension.injector.Injector
 
 import org.scalatest.BeforeAndAfterAll
@@ -36,6 +37,8 @@ class ComponentSuite extends AnyFunSuite with BeforeAndAfterAll {
   private val e = new DummyComponentE()
   e.ensureRegistered()
 
+  private val classPath: String = System.getProperty("java.class.path")
+
   test("Load order - sanity") {
     val possibleOrders =
       Set(
@@ -44,7 +47,7 @@ class ComponentSuite extends AnyFunSuite with BeforeAndAfterAll {
         Seq(b, a, c, d, e),
         Seq(b, a, d, c, e)
       )
-
+    System.setProperty("java.class.path", "")
     assert(possibleOrders.contains(Component.sorted()))
   }
 
@@ -53,6 +56,18 @@ class ComponentSuite extends AnyFunSuite with BeforeAndAfterAll {
       new DummyBackendA().ensureRegistered()
     }
   }
+
+  test("Discover without component class") {
+    System.setProperty("java.class.path", classPath)
+    assertThrows[GlutenException](Discovery.discoverAll())
+  }
+
+  // Gluten attempts to load from the "classes" directory instead of "test-classes,"
+  // but the META-INF is not located in the "classes" directory.
+  test("Discover without component class again") {
+    System.setProperty("java.class.path", "")
+    assert(Discovery.discoverAll().isEmpty)
+  }
 }
 
 object ComponentSuite {