Configuration#get return value optimization (jeagles)

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/Configuration.java

@@ -619,42 +619,44 @@ public class Configuration implements Iterable<Map.Entry<String,String>>,
    * deprecated key, the value of the deprecated key is set as the value for
    * the provided property name.
    *
+   * @param deprecations deprecation context
    * @param name the property name
    * @return the first property in the list of properties mapping
    *         the <code>name</code> or the <code>name</code> itself.
    */
   private String[] handleDeprecation(DeprecationContext deprecations,
-      String name) {
+                                     String name) {
     if (null != name) {
       name = name.trim();
     }
-    ArrayList<String > names = new ArrayList<String>();
-	if (isDeprecated(name)) {
-      DeprecatedKeyInfo keyInfo = deprecations.getDeprecatedKeyMap().get(name);
-      if (keyInfo != null) {
-        if (!keyInfo.getAndSetAccessed()) {
-          logDeprecation(keyInfo.getWarningMessage(name));
-        }
-
-        for (String newKey : keyInfo.newKeys) {
-          if (newKey != null) {
-            names.add(newKey);
-          }
+    // Initialize the return value with requested name
+    String[] names = new String[]{name};
+    // Deprecated keys are logged once and an updated names are returned
+    DeprecatedKeyInfo keyInfo = deprecations.getDeprecatedKeyMap().get(name);
+    if (keyInfo != null) {
+      if (!keyInfo.getAndSetAccessed()) {
+        logDeprecation(keyInfo.getWarningMessage(name));
+      }
+      // Override return value for deprecated keys
+      names = keyInfo.newKeys;
+    }
+    // If there are no overlay values we can return early
+    Properties overlayProperties = getOverlay();
+    if (overlayProperties.isEmpty()) {
+      return names;
+    }
+    // Update properties and overlays with reverse lookup values
+    for (String n : names) {
+      String deprecatedKey = deprecations.getReverseDeprecatedKeyMap().get(n);
+      if (deprecatedKey != null && !overlayProperties.containsKey(n)) {
+        String deprecatedValue = overlayProperties.getProperty(deprecatedKey);
+        if (deprecatedValue != null) {
+          getProps().setProperty(n, deprecatedValue);
+          overlayProperties.setProperty(n, deprecatedValue);
         }
       }
     }
-    if(names.size() == 0) {
-    	names.add(name);
-    }
-    for(String n : names) {
-	  String deprecatedKey = deprecations.getReverseDeprecatedKeyMap().get(n);
-	  if (deprecatedKey != null && !getOverlay().containsKey(n) &&
-	      getOverlay().containsKey(deprecatedKey)) {
-	    getProps().setProperty(n, getOverlay().getProperty(deprecatedKey));
-	    getOverlay().setProperty(n, getOverlay().getProperty(deprecatedKey));
-	  }
-    }
-    return names.toArray(new String[names.size()]);
+    return names;
   }
  
   private void handleDeprecation() {