Index: lucene/core/src/java/org/apache/lucene/util/RamUsageEstimator.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/util/RamUsageEstimator.java	(revision 1499915)
+++ lucene/core/src/java/org/apache/lucene/util/RamUsageEstimator.java	(working copy)
@@ -213,11 +213,7 @@
     int objectAlignment = 8;
     try {
       final Class<?> beanClazz = Class.forName("com.sun.management.HotSpotDiagnosticMXBean");
-      final Object hotSpotBean = ManagementFactory.newPlatformMXBeanProxy(
-        ManagementFactory.getPlatformMBeanServer(),
-        "com.sun.management:type=HotSpotDiagnostic",
-        beanClazz
-      );
+      final Object hotSpotBean = getHotSpotDiagnosticsMXBean(beanClazz);
       final Method getVMOptionMethod = beanClazz.getMethod("getVMOption", String.class);
       final Object vmOption = getVMOptionMethod.invoke(hotSpotBean, "ObjectAlignmentInBytes");
       objectAlignment = Integer.parseInt(
@@ -272,6 +268,33 @@
     return supportedFeatures.size() == JvmFeature.values().length;
   }
 
+  /**
+   * Try to get the diagnostic mxbean without calling {@link ManagementFactory#getPlatformMBeanServer()}
+   * which starts AWT thread (and shows junk in the dock) on a Mac.
+   */
+  private static Object getHotSpotDiagnosticsMXBean(Class<?> beanClazz) throws Exception {
+    // Java 7+, HotSpot
+    try {
+      return ManagementFactory.class.getMethod("getPlatformMXBean", Class.class).invoke(null, beanClazz);
+    } catch (Exception e) {
+      // ignore.
+    }
+    
+    // Java 6, HotSpot
+    try {
+      Class<?> sunMF = Class.forName("sun.management.ManagementFactory");
+      return sunMF.getMethod("getDiagnosticMXBean").invoke(null);
+    } catch (Exception e) {
+      // Ignore.
+    }
+
+    // Last resort option is an attempt to get it from ManagementFactory's server anyway.
+    final Object hotSpotBean = ManagementFactory.newPlatformMXBeanProxy(
+        ManagementFactory.getPlatformMBeanServer(), 
+        "com.sun.management:type=HotSpotDiagnostic", beanClazz);
+    return hotSpotBean;
+  }
+
   /** 
    * Aligns an object size to be the next multiple of {@link #NUM_BYTES_OBJECT_ALIGNMENT}. 
    */