YARN-9824. Fall back to configured queue ordering policy class name

Author: hungj

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/capacity/CapacitySchedulerConfiguration.java

@@ -1552,20 +1552,23 @@ public QueueOrderingPolicy getQueueOrderingPolicy(String queue,
     }
 
     String policyType = get(getQueuePrefix(queue) + ORDERING_POLICY,
-        defaultPolicy);
+        defaultPolicy).trim();
 
     QueueOrderingPolicy qop;
-    if (policyType.trim().equals(QUEUE_UTILIZATION_ORDERING_POLICY)) {
+    if (policyType.equals(QUEUE_UTILIZATION_ORDERING_POLICY)) {
       // Doesn't respect priority
       qop = new PriorityUtilizationQueueOrderingPolicy(false);
-    } else if (policyType.trim().equals(
+    } else if (policyType.equals(
         QUEUE_PRIORITY_UTILIZATION_ORDERING_POLICY)) {
       qop = new PriorityUtilizationQueueOrderingPolicy(true);
     } else {
-      String message =
-          "Unable to construct queue ordering policy=" + policyType + " queue="
-              + queue;
-      throw new YarnRuntimeException(message);
+      try {
+        qop = (QueueOrderingPolicy) Class.forName(policyType).newInstance();
+      } catch (Exception e) {
+        String message = "Unable to construct queue ordering policy="
+            + policyType + " queue=" + queue;
+        throw new YarnRuntimeException(message, e);
+      }
     }
 
     return qop;