为什么数字会自动加倍？ [英] Why is a number casted automatically to double?

问题描述

我为我的webservice使用spring启动。每个方法返回 Map< Object，Object> ，因为它是一个通用类型，并且方法能够返回任何响应，原始 int 或复杂的自定义对象 User 。另外，我使用 Map< Object，Object> 来消除JSON中的反斜杠\，而不是使用String。

I use spring boot for my webservice. Each method returns Map<Object, Object> because it is a general type and the methods are able to return any response, either a primitive int or complex custom object of User. Also I used Map<Object, Object> to eliminate backslash "\" in JSON, instead of using String.

但是我在客户端（Android应用程序）中有变量转换的问题。

But I got problem with variable casting in client (Android app).

Map中的数字变量自动转换为double（1.0,2.0,3.0,5.0， ..），而在服务器中 long 。

Number variables in Map are automatically casted to double (1.0, 2.0, 3.0, 5.0, ...) while it is long in server.

如果我在服务器上将数字转换为字符串，客户是正确的例如1，2，3，5，...

If I cast number to string at server, then casting at client is right e.g. 1, 2, 3, 5, ...

return String.valueOf(u.getId())

服务器端变量：

long id;

服务器端方法：

public final static String SUCCESS = "0";
public final static String NOT_FOUND = "-1";

Map<Object, Object> m = new HashMap<>();

@RequestMapping("/getUser")
Map<Object, Object> getUser(@RequestParam(value = "phoneNumber", defaultValue = "") String phoneNumber,
        @RequestParam(value = "hash", defaultValue = "") String hash) {

    m.clear();

    User user = userRepository.findByPhoneNumberAndHash(phoneNumber, hash);
    if (user != null) {
        m.put(ERROR_JSON, SUCCESS);
        m.put(VALUE_JSON, user);
    } else {
        m.put(ERROR_JSON, NOT_FOUND);
    }
    return m;
}

JSON：

[{"id":1}] and [{"id":"1"}]

Android代码。改造

Android code. Retrofit

userService.getUser(phoneNumber, hash).enqueue(new Callback<Map<Object, Object>>() {

    @Override
    public void onResponse(Call<Map<Object, Object>> call, Response<Map<Object, Object>> response) {
        Map<Object, Object> m = response.body();
    }
    @Override
    public void onFailure(Call<Map<Object, Object>> call, Throwable t) {
        t.printStackTrace();
    }
});

推荐答案

JSON是一个JavaScript对象。在javascript中，没有longs或float或double。一切都是一个数字，它都在后台使用双。所以当你发送JSON，除非你告诉它解释一个值为一个明确的长度，它必须假设它可以是任何有效的数字 - 它必须假设一个双。

JSON is a JavaScript Object. In javascript, there are no longs or floats or doubles. Everything is a number, and it all uses double in the background. So when you send JSON, unless you tell it to interpret a value as a long explicitly, it has to assume it could be any valid number- it has to assume its a double.

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