How to create ring shape drawable in android?

I think using a shape in android is better than a shape in photoshop.

Correct, creating a drawable it's better because you can change the colour or shape with code instead of creating a new image resource, for example. Create a FrameLayout with 2 Views and a TextView. The first view background would be your outer ring (shape) and the second a filed circle (shape). Finally the last View (bigger z-index) your TextView:

<FrameLayout>
   <View/><!-- (outer ring)-->
   <View/><!-- (filed circle)-->
   <TextView/><!-- (text)-->
</FrameLayout>

You will need to create a drawable and set it as a background.

shape_primary_ring.xml

<shape
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:innerRadiusRatio="2.5"
    android:shape="ring"
    android:thickness="4dp"
    android:useLevel="false">

    <solid android:color="@color/colorPrimary"/>

</shape>

Preview

Ring drawable is juxtaposition of elements, use layer-list

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
  <item android:right="6dip" android:left="6dip">
    <shape xmlns:android="http://schemas.android.com/apk/res/android"
           android:innerRadius="0dp"
           android:shape="ring"
           android:thicknessRatio="3"
           android:useLevel="false" >
      <solid android:color="@android:color/transparent" />
      <stroke
          android:width="5dp"
          android:color="@color/maroon" />
    </shape>
  </item>
  <item android:right="20dip"
        android:left="20dip"
        android:bottom="0dip"
        android:top="34dip">
    <shape xmlns:android="http://schemas.android.com/apk/res/android"
           android:shape="rectangle"
           android:innerRadius="0dp">
      <solid android:color="@color/maroon" />
      <stroke android:width="1dip" android:color="@android:color/transparent" />
    </shape>
  </item>
  <item android:right="20dip"
        android:left="20dip"
        android:bottom="34dip"
        android:top="0dip">
    <shape xmlns:android="http://schemas.android.com/apk/res/android"
           android:shape="rectangle"
           android:innerRadius="0dp">
      <solid android:color="@color/maroon" />
      <stroke android:width="1dip" android:color="@android:color/transparent" />
    </shape>
  </item>
</layer-list>

Xml drawable by all means more useful than static images, they can be correctly scaled without need of .9 library or generating set of different sizes from Gimp, Photoshop

2dp outer ring with a 2dp gap:

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:top="4dp"
        android:right="4dp"
        android:bottom="4dp"
        android:left="4dp">
        <shape
            android:shape="oval">
            <solid android:color="#4d4d4d" />
        </shape>
    </item>
    <item>
        <shape
            android:shape="oval">
            <stroke android:width="2dp"
                android:color="#4d4d4d"/>
        </shape>
    </item>
</layer-list>