```
public static void main(String[] args) {

    Gson g = new GsonBuilder()
            .setPrettyPrinting()
            .enableComplexMapKeySerialization()
            .serializeSpecialFloatingPointValues()
            .setLongSerializationPolicy(LongSerializationPolicy.DEFAULT)
            .setPrettyPrinting()
            //.registerTypeAdapter(HashMap.class, new HashMapDeserializer())
            .create();

    HashMap<Object, Object> h = new HashMap<Object, Object>();
    h.put("num1", 10);
    h.put("num2", 20);
    h.put("num3", 20.0);
    h.put("num4", "<>");
    h.put("num5", "~!@#$%^&*()_+=-`,.<>?/:;[]{}|");

    String jsonStr = g.toJson(h);
    System.out.println("JsonString::"+jsonStr);
    /*Output below ::
     * 
        JsonString::{
            "num4": "\u003c\u003e",
            "num5": "~!@#$%^\u0026*()_+\u003d-`,.\u003c\u003e?/:;[]{}|",
            "num2": 20,
            "num3": 20.0,
            "num1": 10
        }
     */

    h = g.fromJson(jsonStr, HashMap.class);

    System.out.println("convert from json String :>"+h);
    /*Output below:
      convert from json String :>{num4=<>, num5=~!@#$%^&*()_+=-`,.<>?/:;[]{}|, num2=20.0, num3=20.0, num1=10.0}
     */

    int num1= (Integer) h.get("num1");
    System.out.println(num1);
}

```

---

```
Exception in thread "main" java.lang.ClassCastException: java.lang.Double cannot be cast to java.lang.Integer
    at com.ps.multiupload.servlet.FileUploadUtil.main(FileUploadUtil.java:52)

```