How to prevent Gson from converting a long number (a json string ) to scientific notation format?

Question

I need to convert json string to java object and display it as a long. The json string is a fixed array of long numbers:

{numbers
[ 268627104, 485677888, 506         


        

Answer 1

We can use the below code solution for number Long:

Document doc = documentCursor.next();  

JsonWriterSettings relaxed = JsonWriterSettings.builder().outputMode(JsonMode.RELAXED).build();  

CustomeObject obj = gson.fromJson(doc.toJson(relaxed), CustomeObject.class);

Answer 2

If serializing to a String is an option for you, you can configure GSON to do so with:

GsonBuilder gsonBuilder = new GsonBuilder();
gsonBuilder.setLongSerializationPolicy( LongSerializationPolicy.STRING );
Gson gson = gsonBuilder.create();

This will produce something like:

{numbers : [ "268627104", "485677888", "506884800" ] }

Answer 3

Got the same issue, after some investigation here is what I found.

The behavior:

• Gson
  For a number without fractional part, Gson would convert it as Double,
• Jackson
  For a number without fractional part, Jackson would convert it as Integer or Long, depends on how large the number is.

Possible solutions:

• Convert Gson's return value from Double to Long, explicitly.
• Use Jackson instead.
  I prefer this.

---

Code - test for Jackson

ParseNumberTest.java:

import java.util.List;

import org.testng.Assert;
import org.testng.annotations.Test;

import com.fasterxml.jackson.databind.ObjectMapper;

/**
 * test - jackson parse numbers,
 * 
 * @author eric
 * @date Jan 13, 2018 12:28:36 AM
 */
public class ParseNumberTest {
    @Test
    public void test() throws Exception {
    String jsonFn = "numbers.json";

    ObjectMapper mapper = new ObjectMapper();

    DummyData dd = mapper.readValue(this.getClass().getResourceAsStream(jsonFn), DummyData.class);
    for (Object data : dd.dataList) {
        System.out.printf("data type: %s, value: %s\n", data.getClass().getName(), data.toString());
        Assert.assertTrue(data.getClass() == Double.class || data.getClass() == Long.class || data.getClass() == Integer.class);

        System.out.printf("%s\n\n", "------------");
    }
    }

    static class DummyData {
    List<Object> dataList;

    public List<Object> getDataList() {
        return dataList;
    }

    public void setDataList(List<Object> dataList) {
        this.dataList = dataList;
    }
    }
}

numbers.json:

{
    "dataList": [
        150000000000,
        150778742934,
        150000,
        150000.0
    ]
}

How to run:

• The test case is based on Jackson & TestNG.
• Put numbers.json at the same package as ParseNumberTest.java.
• Run as testng test, then it would print type & value of the parse result.

Output:

data type: java.lang.Long, value: 150000000000
------------

data type: java.lang.Long, value: 150778742934
------------

data type: java.lang.Integer, value: 150000
------------

data type: java.lang.Double, value: 150000.0
------------

PASSED: test

Answer 4

I did not find a solution to my problem of gson formatting numbers ending in 0 to scientific notation. I instead used a work-around to convert this scientific notation into a double that I formatted with commas. "value" is the json string.

  private String formatNumber(String value) { 
    double dValue = Double.parseDouble(value);
    String pattern = "#,###";
    DecimalFormat formatter = new DecimalFormat(pattern);
    String newNumber = formatter.format(dValue);

            return newNumber;
}

This doesn't answer the question asked but is an added step to work-around the problem to display the numbers as required by the system.

Answer 5

Another work around is to use the JsonParser class instead. This will return the Gson object representations (JsonElement) rather than a user defined class, but avoids the problem of conversion to scientific notation.

import java.lang.reflect.Type;
import java.util.Map;

import com.google.gson.Gson;
import com.google.gson.JsonElement;
import com.google.gson.JsonParser;
import com.google.gson.reflect.TypeToken;

public class GsonTest
{
    public static void main(String[] args)
    {
        String json = "{numbers:[268627104,485677888,506884800]}";

        Gson gson = new Gson();
        Type type = new TypeToken<Map<String, Object>>(){}.getType();
        Map<String, Object> jsonMap = gson.fromJson(json, type);
        System.out.println("Gson output:");
        System.out.println(jsonMap);

        JsonParser jsonParser = new JsonParser();
        JsonElement jsonElement = jsonParser.parse(json);
        System.out.println("JsonParser output:");
        System.out.println(jsonElement);
    }
}

Code Output:

Gson output:  
{numbers=[2.68627104E8, 4.85677888E8, 5.068848E8]}  
JsonParser output:  
{"numbers":[268627104,485677888,506884800]}

Answer 6

I had a similar problem, and it not only converts integers to double, but it actually loses precision for certain long numbers, as described in this related question.

I tracked down this conversion to ObjectTypeAdapter's read method, specifically:

case NUMBER:
  return in.nextDouble();

It may be possible to plug in a modified TypeAdapter for Object, but I couldn't get that to work, so instead I just copied the read method (Object read(JsonReader in)) to my own code and modified the above lines to this:

case NUMBER:
    final String s = in.nextString();
    try {
        return Integer.parseInt(s);
    } catch (NumberFormatException e) {
        // ignore
    }
    try {
        return Long.parseLong(s);
    } catch (NumberFormatException e) {
        // ignore
    }
    return Double.parseDouble(s);

I wish Gson did this by default..

Then I put the other connecting pieces in a helper method that looks something like this:

public static Object parse(final Reader r) {
    try (final JsonReader jr = new JsonReader(r)) {
        jr.setLenient(true);
        boolean empty = true;
        Object o = null;
        try {
            jr.peek();
            empty = false;
            o = read(jr);
        } catch (EOFException e) {
            if (!empty) {
                throw new JsonSyntaxException(e);
            }
        }
        if (o != null && jr.peek() != JsonToken.END_DOCUMENT) {
            throw new JsonIOException("JSON document was not fully consumed.");
        }
        return o;
    } catch (IOException e) {
        throw new JsonIOException(e);
    }
}

So now instead of new Gson().fromJson(r, Object.class), I call parse(r).

This works well for me because I want to be able to parse json data with any structure, but if you have a particular class you're targeting, you probably just need to eliminate occurrences of Object within that class's members.