google cloud endpoints returning java long as string in JSON

问题

I am using google app engine latest version 1.9.30 and I define my cloud endpoint as follows

@Api(name="app", version="v1", transformers={EndpointDateTransformer.class})
public class MyEndpoints {

    @ApiMethod(name="dummy", path="dummy", httpMethod=HttpMethod.GET)
    public Map<String, Object> dummy(){
        Map<String, Object> dummy = Maps.newHashMap();
        dummy.put("date", DateUtil.getCurrentTimestamp());
        dummy.put("number", 5L);
        return dummy;
    }

}

here EndpointDateTransformer converts Date to Long value and the JSON response from endpoint is

{
    "number": "5",
    "date": "1452751174672"
}

But if I change that 5L to 5 then I see JSON response as

{
    "number": 5,
    "date": "1452751174672"
}

Why cloud endpoints converting Long values as string in JSON. When I was working on old app engine versions 1.9.19 it used to work. Long rendered as long on JSON as well. Am I missing anything here?

回答1:

JSON is JavaScript Object Notation, it's a valid Javascript actually. So it should follow javascript standards.

Javascript's Number is 54 bit number, from -(2^53 - 1) to (2^53 - 1). But Java's long is 64 bit number, from -2^63 to 2^63-1.

See difference:

Java Long Max         = 9223372036854775807
Javascript Number Max = 9007199254740992

You simply cannot convert Java Long to Javascript Number because it doesn't work for all values. So a string representation is used instead.

You have two possible solutions:

define your value as Integer
use an entity object with custom transformer, see https://cloud.google.com/appengine/docs/java/endpoints/annotations#apitransformer

Or if you really want Date, it's better to format it as yyyy-MM-dd\'T\'HH:mm:ss within UTC timezone. It's compatible with Javascript date format.

Specs:

Javascript - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number
Java - https://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html
Javascript Date - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date

来源：https://stackoverflow.com/questions/34783049/google-cloud-endpoints-returning-java-long-as-string-in-json

标签

java

json

google-app-engine

google-cloud-endpoints