如何检查json键是否存在?

So, I get some JSON values from the server but I don't know if there will be a particular field or not.

因此，我从服务器获得一些JSON值，但我不知道是否会有一个特定字段。

So like:

就像:

{ "regatta_name":"ProbaRegatta",
  "country":"Congo",
  "status":"invited"
}

And sometimes, there will be an extra field like:

有时，会有一个额外的领域，比如:

{ "regatta_name":"ProbaRegatta",
  "country":"Congo",
  "status":"invited",
  "club":"somevalue"
}

I would like to check if the field named "club" exists so that at parsing I won't get org.json.JSONException: No value for club

我想检查名为“club”的字段是否存在，以便在解析时不会获得org.json。JSONException:俱乐部没有价值。

8 个解决方案

#1

JSONObject class has a method named "has":

JSONObject类有一个名为“has”的方法:

http://developer.android.com/reference/org/json/JSONObject.html#has(java.lang.String)

http://developer.android.com/reference/org/json/JSONObject.html(以)

Returns true if this object has a mapping for name. The mapping may be NULL.

如果该对象具有名称映射，则返回true。映射可能为空。

#2

You can check this way where 'HAS' - Returns true if this object has a mapping for name. The mapping may be NULL.

您可以这样检查'HAS' -如果这个对象有名称的映射返回true。映射可能为空。

if (json.has("status")) {
   String status = json.getString("status"));
}

if (json.has("club")) {
   String club = json.getString("club"));
}

You can also check using 'isNull' - Returns true if this object has no mapping for name or if it has a mapping whose value is NULL.

您还可以使用'isNull'检查—如果这个对象没有名称映射，或者它有一个值为NULL的映射，则返回true。

if (!json.isNull("club"))
    String club = json.getString("club"));

#3

you could JSONObject#has, providing the key as input and check if the method returns true or false. You could also

您可以将JSONObject#作为输入提供键，并检查方法是否返回true或false。你也可以

use optString instead of getString:

使用optString代替getString:

Returns the value mapped by name if it exists, coercing it if necessary. Returns the empty string if no such mapping exists

返回按名称映射的值(如果存在)，必要时强制它。如果不存在这种映射，则返回空字符串

#4

You can use has

您可以使用了

public boolean has(String key)

Determine if the JSONObject contains a specific key.

确定JSONObject是否包含特定的键。

Example

例子

JSONObject JsonObj = new JSONObject(Your_API_STRING); //JSONObject is an unordered collection of name/value pairs

if (JsonObj.has("address")) { 
    //Checking address Key Present or not
    String get_address = JsonObj .getString("address"); // Present Key
}
else {
    //Do Your Staff
}

#5

just before read key check it like before read

在阅读前，像阅读前一样检查它

JSONObject json_obj=new JSONObject(yourjsonstr);
if(json_obj.isNull("club"))
{
  //it's contain value to be read operation
}
else
{
  //it's not contain key club or isnull so do this operation here
}

isNull function definition

isNull函数定义

Returns true if this object has no mapping for name or
if it has a mapping whose value is NULL. 

official documentation below link for isNull function

isNull函数的链接下面的官方文档

http://developer.android.com/reference/org/json/JSONObject.html#isNull(java.lang.String)

http://developer.android.com/reference/org/json/JSONObject.html isNull(以)

#6

Try this

试试这个

if(!jsonObj.isNull("club")){
    jsonObj.getString("club");
}

#7

A better way, instead of using a conditional like:

更好的方法，而不是使用条件类:

if (json.has("club")) {
    String club = json.getString("club"));
 }

is to simply use the existing method optString(), like this:

是简单地使用现有的方法optString()，如下所示:

String club = json.optString("club);

the optString("key") method will return an empty String if the key does not exist and won't, therefore, throw you an exception.

optString(“key”)方法将返回一个空字符串，如果该键不存在，因此不会抛出异常。

#8

I used hasOwnProperty('club')

var myobj = { "regatta_name":"ProbaRegatta",
    "country":"Congo",
    "status":"invited"
 };

 if ( myobj.hasOwnProperty("club"))
     // do something with club (will be false with above data)
     var data = myobj.club;
 if ( myobj.hasOwnProperty("status"))
     // do something with the status field. (will be true with above ..)
     var data = myobj.status;

works in all current browsers.

适用于所有当前浏览器。