How to check if a JSON key exists?

Question

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

So like:

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

And sometimes, there will be an extra field like:

{ "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

if(jsonObject.getString("club")!=null){ //get the vale here } — Software Sainath, Jul 05 '13 at 10:55
No, at the exception handling the code stops, and further parse actions wont run. — Adam Varhegyi, Jul 05 '13 at 10:56
String clubvalue="";try(clubvalue=jsonobject.getString("club");}catch(Exception e){ } — Software Sainath, Jul 05 '13 at 10:59

score 337 · Accepted Answer · answered Jul 05 '13 at 10:57

337

JSONObject class has a method named "has":

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

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

answered Jul 05 '13 at 10:57

PX Developer

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What if the key is from `Integer` type? – Eido95 May 15 '17 at 19:33
2

@Eido95 having an `Integer` as a key sounds like bad practice. JSON should be with a String key and a value of whatever you need. – Nico Jul 24 '17 at 11:11
@Eido95, I believe for an integer there is always a value, every time you declare an integer, you have to initialize it with a value. – mut tony Feb 09 '18 at 18:54

score 180 · Answer 2 · edited Mar 12 '18 at 05:48

180

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

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.

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

edited Mar 12 '18 at 05:48

Reaz Murshed

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answered Jul 05 '13 at 11:07

Nirali

13,571
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3

which json lib are you using, can you provide a simple example for json-smart or json-simple – Samuel Owino Sep 11 '17 at 09:39
@samuelowino json is the variable wich contains your object – Fernando Torres May 05 '19 at 05:36

Blackbelt · Answer 3 · 2017-02-01T11:17:59.677

19

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

use optString instead of getString:

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

edited Feb 01 '17 at 11:17

answered Jul 05 '13 at 10:56

Blackbelt

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1

Although this method of may be of use for others, this does not return if the value exists. If `getString` would have returned an empty string, `optString` would also return an empty string. Assumption would then have you believe that the property isn't available in OP's situation. – halfpastfour.am Aug 16 '14 at 18:56
@Blackbelt do you have sources for this? – Taku Oct 06 '16 at 18:37

score 18 · Answer 4 · edited Mar 16 '19 at 22:33

just before read key check it like before read

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

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

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

IntelliJ Amiya · Answer 5 · 2017-08-23T09:28:47.543

10

You can use has

public boolean has(String key)

Determine if the JSONObject contains a specific key.

Example

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
}

edited Aug 23 '17 at 09:28

answered Jul 23 '16 at 08:41

IntelliJ Amiya

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score 7 · Answer 6 · answered Nov 22 '17 at 23:34

7

A better way, instead of using a conditional like:

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

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

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.

answered Nov 22 '17 at 23:34

fuzzKitty

334
3
7

I had no idea this existed until your answer. Thanks a bunch. – DevOpsSauce Dec 01 '20 at 04:37
Very Good Answer – Islam Alshnawey Aug 27 '21 at 06:15

score 3 · Answer 7 · answered Aug 07 '19 at 13:27

3

Try this:

let json=yourJson

if(json.hasOwnProperty(yourKey)){
    value=json[yourKey]
}

answered Aug 07 '19 at 13:27

Aishwarya

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score 3 · Answer 8 · edited Sep 24 '19 at 14:13

3

Json has a method called containsKey().

You can use it to check if a certain key is contained in the Json set.

File jsonInputFile = new File("jsonFile.json"); 
InputStream is = new FileInputStream(jsonInputFile);
JsonReader reader = Json.createReader(is);
JsonObject frameObj = reader.readObject();
reader.close();

if frameObj.containsKey("person") {
      //Do stuff
}

edited Sep 24 '19 at 14:13

Christoph Grimmer

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answered Sep 24 '19 at 13:17

Udana Methmal

37
6

score 1 · Answer 9 · answered Jul 05 '13 at 11:10

1

Try this

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

answered Jul 05 '13 at 11:10

R9J

6,605
4
19
25

3

`isNull` is actually for to check if mapping is null, not for checking availability of a json member. – Reza_Rg Jul 22 '15 at 05:09

score 1 · Answer 10 · answered May 19 '18 at 02:59

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.

score 1 · Answer 11 · answered Aug 24 '19 at 21:05

1

You can try this to check wether the key exists or not:

JSONObject object = new JSONObject(jsonfile);
if (object.containskey("key")) {
  object.get("key");
  //etc. etc.
}

answered Aug 24 '19 at 21:05

Dorus Blanken

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1
9

score 0 · Answer 12 · answered Aug 06 '18 at 14:07

I am just adding another thing, In case you just want to check whether anything is created in JSONObject or not you can use length(), because by default when JSONObject is initialized and no key is inserted, it just has empty braces {} and using has(String key) doesn't make any sense.

So you can directly write if (jsonObject.length() > 0) and do your things.

Happy learning!

score 0 · Answer 13 · answered Jun 08 '20 at 15:29

0

You can use the JsonNode#hasNonNull(String fieldName), it mix the has method and the verification if it is a null value or not

answered Jun 08 '20 at 15:29

Tiago Coelho

1

How to check if a JSON key exists?

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