无法在JSON对象中放入空值 [英] Unable to put null values in JSON object

问题描述

我正在尝试使用JSON将参数传递给api.

I am trying to pass parameter to api using JSON.

class Sample
{ ...
   String token;
...

void method()
{ ...
    JSONObject params = new JSONObject();
    params.put(KEY_TOKEN,token);
    params.put(KEY_DATE,date);

    Log.e("params ",params+"");


      ...  }    

我将params的值设置为{"date":"2017-06-19"}，但没有地方看到令牌. 我尚未初始化令牌，并且其值为null作为其实例变量.难道没有包含未初始化的值吗?

I get the value of params as {"date":"2017-06-19"} but token is seen nowhere. I have not initialized token and its value is null as its an instance variable. So is it something that uninitialized value are not included?

推荐答案

文档，在第一段中:

值不能为null，NaN，无穷大或此处未列出的任何类型.

Values may not be null, NaNs, infinities, or of any type not listed here.

是的，这是"...一些不包含null值的东西..." (这是您原始问题的引文；您已更新的问题将其更改为未初始化的值"，但对象引用的默认值为null，所以...)

So yes, it is "...something that null values are not included..." (edit: that was a quote from your original question; your updated question changes it to "uninitialized values" but the default value of an object reference is null, so...)

这是该类的功能"； JSON 本身可以理解null.在文档的更下方，它说您使用了正弦值"， ，代表null.似乎...很奇怪.有一个关于它的注释:

It's a "feature" of that class, though; JSON itself understands null just fine. Further down in the documentation it says you use a "sentinal value," NULL, to represent null. Which seems...odd. There's a note about it:

警告:此类以两种不兼容的方式表示null:标准Java null引用和标记值NULL.特别是，调用put(name, null)会从对象中删除命名的条目，但是put(name, JSONObject.NULL)会存储一个值为JSONObject.NULL的条目.

Warning: this class represents null in two incompatible ways: the standard Java null reference, and the sentinel value NULL. In particular, calling put(name, null) removes the named entry from the object but put(name, JSONObject.NULL) stores an entry whose value is JSONObject.NULL.

所以:

params.put(KEY_TOKEN, token == null ? JSONObject.NULL : token);

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