HDDS-4769. Simplify insert operation of ContainerAttribute

hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/container/states/ContainerAttribute.java

@@ -84,7 +84,8 @@ public ContainerAttribute() {
   }
 
   /**
-   * Insert or update the value in the Attribute map.
+   * Insert the value in the Attribute map, keep the original value if it exists
+   * already.
    *
    * @param key - The key to the set where the ContainerID should exist.
    * @param value - Actual Container ID.
@@ -93,30 +94,8 @@ public ContainerAttribute() {
   public boolean insert(T key, ContainerID value) throws SCMException {
     Preconditions.checkNotNull(key);
     Preconditions.checkNotNull(value);
-
-    if (attributeMap.containsKey(key)) {
-      if (attributeMap.get(key).add(value)) {
-        return true; //we inserted the value as it doesn’t exist in the set.
-      } else { // Failure indicates that this ContainerID exists in the Set
-        if (!attributeMap.get(key).remove(value)) {
-          LOG.error("Failure to remove the object from the Map.Key:{}, " +
-              "ContainerID: {}", key, value);
-          throw new SCMException("Failure to remove the object from the Map",
-              FAILED_TO_CHANGE_CONTAINER_STATE);
-        }
-        attributeMap.get(key).add(value);
-        return true;
-      }
-    } else {
-      // This key does not exist, we need to allocate this key in the map.
-      // TODO: Replace TreeSet with FoldedTreeSet from HDFS Utils.
-      // Skipping for now, since FoldedTreeSet does not have implementations
-      // for headSet and TailSet. We need those calls.
-      this.attributeMap.put(key, new TreeSet<>());
-      // This should not fail, we just allocated this object.
-      attributeMap.get(key).add(value);
-      return true;
-    }
+    attributeMap.computeIfAbsent(key, any -> new TreeSet<>()).add(value);
+    return true;
   }
 
   /**

hadoop-hdds/server-scm/src/test/java/org/apache/hadoop/hdds/scm/container/states/TestContainerAttribute.java

@@ -45,7 +45,7 @@ public void testInsert() throws SCMException {
         containerAttribute.getCollection(1).size());
     Assert.assertTrue(containerAttribute.getCollection(1).contains(id));
 
-    // Insert again and verify that it overwrites an existing value.
+    // Insert again and verify that the new ContainerId is inserted.
     ContainerID newId =
         new ContainerID(42);
     containerAttribute.insert(1, newId);