implicit typecasting

[Faisal-Alsumait]

Gson version

2.9.1

Java

java 15.0.1

Used tools

Maven 3.8.1

Description

When mapping String to Object using fromJson method, wrong implicit typecasting was performed

Expected behavior

correct implicit typecasting .

Actual behavior

wrong implicit typecasting .

Reproduction steps

        Gson gson = new Gson();
        String integerNumber = "9";
        String longNumber = "999999999999";
        Object integerValue = gson.fromJson(integerNumber, Object.class);
        Object longValue = gson.fromJson(longNumber, Object.class);
        System.out.println(integerValue.getClass()); //  Expected behavior: class java.lang.Integer, Actual behavior: class java.lang.Double
        System.out.println(longValue.getClass()); //  Expected behavior: class java.lang.Long, Actual behavior: class java.lang.Double

[Marcono1234]

This is intended. For backward compatibility when Gson is told to deserialize Object.class and encounters a JSON number it will by default always deserialize it as Double.

To account for use cases where this is not desired Gson provides a ToNumberStrategy which allows customizing this behavior. Gson has some built-in strategies provided by ToNumberPolicy, but none of those seems to be what you are looking for. Though you can implement your own in a similar way to how LONG_OR_DOUBLE is implemented:

gson/gson/src/main/java/com/google/gson/ToNumberPolicy.java

Lines 66 to 81 in ea7ab7c

	@Override public Number readNumber(JsonReader in) throws IOException, JsonParseException {
	String value = in.nextString();
	try {
	return Long.parseLong(value);
	} catch (NumberFormatException longE) {
	try {
	Double d = Double.valueOf(value);
	if ((d.isInfinite() || d.isNaN()) && !in.isLenient()) {
	throw new MalformedJsonException("JSON forbids NaN and infinities: " + d + "; at path " + in.getPreviousPath());
	}
	return d;
	} catch (NumberFormatException doubleE) {
	throw new JsonParseException("Cannot parse " + value + "; at path " + in.getPreviousPath(), doubleE);
	}
	}
	}

See also #1290 which added this feature and contains some more background information about this feature.