Use String instead of Double do your calculations on double the convert value to String.ValueOf(sum) and set value to your statistics POJO.

Convert your POJO like below

public class Statics {
private String sum;
private String avg;
private String max;
private String min;
private Long count = Long.valueOf(0);//getter and setters and constructrures
}

All numbers are floats in Javascript. So, 1.0 and 1 are the same in JS. There is no differenciation of int, float and double.

Since JSON is going to end up as a JS object, there is no use in adding an extra '.0' since '1' represents a float as well. I guess this is done to save a few bytes in the string that is passed around.

So, you will get a float in JS, and if you parse it back to Java, you should get a double. Try it.

In the mean time, if you are interested in the way it displays on screen, you can try some string formatting to make it look like '1.0'.

Since unitfactor is of type string, If you cannot change JSON then you can use

double mUnitFactor = Double.parseDouble(fbeObject.getString("unitfactor"))

You could either use @JsonSerialize with ToStringSerializer:

@Data
public class MyBean {

    @JsonSerialize(using = ToStringSerializer.class)
    private double myDouble;
}

Or use @JsonFormat with JsonFormat.Shape.STRING:

@Data
public class MyBean {

    @JsonFormat(shape = Shape.STRING)
    private double myDouble;
}

Both approaches produce the same result.

If you intend to use these annotations in multiple places, you may consider @JacksonAnnotationsInside which allows you to create a custom annotation which contains one or more Jackson annotations:

@Retention(RUNTIME)
@JacksonAnnotationsInside
@JsonSerialize(using = ToStringSerializer.class)
public @interface JsonString {

}

@Data
public class MyBean {

    @JsonString
    private double myDouble;
}

You can use:

JSONObject jsonObject = new JSONObject();
jsonObject.toString();

And if you want to get a specific value, you can use:

jsonObject.getString("msg");

or Integer value

jsonObject.getInt("codeNum");

For long Integers

jsonObject.getLong("longNum");

I am not sure my solution is acceptable since it does require additional explicit call to ObjectMapper to perform deserialization of the string value of Message.
However, this is it is done during the buildup of Notification object and does not require a String message property.

You need to add a ctor with String argument to Message class, where you can deserialize the String into Map and extract the instance propertieds:

public Message(String str) {
    try {
        @SuppressWarnings("unchecked")
        Map<String, Object> map = 
                (Map<String, Object>)new ObjectMapper().readValue(str, Map.class);
        language = map.containsKey("language") ? map.get("language").toString() : null ;
        data = map.containsKey("data") ? map.get("data").toString() : null ;
    } catch (Exception e) {
        e.printStackTrace();
    }
}

the new ctor will be called by Jackson when you deserialize a Notification object:

Notification n = (Notification)new ObjectMapper().readValue(reader, Notification.class);

Using Double.toString(), if the number is too small or too large, you will get a scientific notation like this: 3.4875546345347673E-6. There are several ways to have more control of output string format.

double num = 0.000074635638;
// use Double.toString()
System.out.println(Double.toString(num));
// result: 7.4635638E-5

// use String.format
System.out.println(String.format ("%f", num));
// result: 0.000075
System.out.println(String.format ("%.9f", num));
// result: 0.000074636

// use DecimalFormat
DecimalFormat decimalFormat = new DecimalFormat("#,##0.000000");
String numberAsString = decimalFormat.format(num);
System.out.println(numberAsString);
// result: 0.000075

Use String.format() will be the best convenient way.

In Java EE 7, use jsonObject.getJsonNumber("key").doubleValue() to get the double value.

See: https://docs.oracle.com/javaee/7/api/javax/json/JsonNumber.html