After a lot of research: This actually works:
getActionBar().setDisplayOptions(ActionBar.DISPLAY_SHOW_CUSTOM);
getActionBar().setCustomView(R.layout.custom_actionbar);
ActionBar.LayoutParams p = new ActionBar.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT);
p.gravity = Gravity.CENTER;
You have to define custom_actionbar.xml layout which is as per your requirement e.g. :
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="50dp"
android:background="#2e2e2e"
android:orientation="vertical"
android:gravity="center"
android:layout_gravity="center">
<ImageView
android:id="@+id/imageView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/top_banner"
android:layout_gravity="center"
/>
</LinearLayout>