Java - Why does Gson parse an integer as a double?

Question

Complex json string and I want to convert it to a map,
I have a problem.
Take a look at this simple test:

public class Test {

    @SuppressWarnings("serial")
    public static void main(String[] args) {
        Map<String, Object> hashMap = new HashMap<String, Object>();
        hashMap.put("data", "{\"rowNum\":0,\"colNum\":2,\"text\":\"math\"}");

        Map<String,Object> dataMap = JsonUtil.getGson().fromJson(
                hashMap.get("data").toString(),new TypeToken<Map<String,Object>>() {}.getType());

        System.out.println(dataMap.toString());

    }
}

Result:
console printing: {rowNum=0.0, colNum=2.0, text=math}
Int converts to Double,
Why does gson change type and how to fix it?

Answer 1

Gson is a simple parser. It always uses Double as the default type of number if you parse data before Object.

Check this question for more information: How to prevent Gson from expressing integers as floats

Jackson Mapper. , :

• "2" Integer
• "2.0" Double

:

Map<String, Object> hashMap = new HashMap<String, Object>();
hashMap.put("data", "{\"rowNum\":0,\"colNum\":2,\"text\":\"math\"}");
ObjectMapper mapper = new ObjectMapper();
TypeReference<HashMap<String, Object>> typeRef = new TypeReference<HashMap<String, Object>>() {};

HashMap<String, Object> o = mapper.readValue(hashMap.get("data").toString(), typeRef);

Maven:

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-core</artifactId>
    <version>2.9.0</version>
</dependency>

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.9.0</version>
</dependency>

Answer 2

JSON , Java. .

, Double, Gson. JSON, Double.

Map POJO, JSON. , Integer.

class Cell {
    private Integer rowNum;
    private Integer colNum;
    private String text;
}

public static void main(String[] args) throws Exception {
    Map<String, Object> hashMap = new HashMap<String, Object>();
    hashMap.put("data", "{\"rowNum\":0,\"colNum\":2,\"text\":\"math\"}");

    Cell cell = new Gson().fromJson(hashMap.get("data").toString(), Cell.class);
    System.out.println(cell);
}