How to test if JSON Collection object is empty in Java

Question

The JSON Collection object I'm receiving looks like this:

[{"foo1":"bar1", "foo2":"bar2", "problemkey": "problemvalue"}]

What I'm trying to test for is the existence of problemvalue. If problemvalue returns a JSON Object, I'm happy. If it doesn't, it will return as {}. How do I test for this condition? I've tried several things to no avail.

This is what I've tried thus far:

//      if (obj.get("dps") == null) {  //didn't work
//      if (obj.get("dps").equals("{}")) {  //didn't work
if (obj.isNull("dps")) {  //didn't work
    System.out.println("No dps key");
}

I expected one of these lines to print "No dps key" because {"dps":{}}, but for whatever reason, it's not. I'm using org.json. The jar file is org.json-20120521.jar.

score 173 · Accepted Answer · answered Jun 09 '14 at 21:18

173

obj.length() == 0

is what I would do.

answered Jun 09 '14 at 21:18

Scott Tesler

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djechlin · Answer 2 · 2018-04-17T12:43:21.723

44

If you're okay with a hack -

obj.toString().equals("{}");

Serializing the object is expensive and moreso for large objects, but it's good to understand that JSON is transparent as a string, and therefore looking at the string representation is something you can always do to solve a problem.

edited Apr 17 '18 at 12:43

answered Oct 04 '13 at 00:04

djechlin

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The best answer – ParSa Jan 29 '20 at 12:20
It adds calculation and cpu load and not so good approach. – Hamid Araghi Jan 17 '21 at 15:36
1

@HamidAraghi not really, the underlying representation is already a `HashMap` with `String` keys, so the conversion is quite speedy. The "faster" approach, if that's necessary for extremely large JSON objects, is to compare the `length()` as demonstrated in other answers. But this approach is hardly slow, even in that case. – Jonathan E. Landrum Feb 25 '21 at 14:56
in my case I had to use .equals("[]") as the object itself came as null. – Smart Coder Oct 25 '22 at 21:01

score 14 · Answer 3 · answered Apr 27 '18 at 10:00

14

If empty array:

.size() == 0

if empty object:

.length() == 0

answered Apr 27 '18 at 10:00

Rohan Lodhi

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score 6 · Answer 4 · answered Oct 03 '13 at 22:51

6

A JSON notation {} represents an empty object, meaning an object without members. This is not the same as null. Neither it is string as you are trying to compare it with string "{}". I don't know which json library are you using, but try to look for method something like:

isEmptyObject()

answered Oct 03 '13 at 22:51

Anderson

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3

thx for your suggestion. i'm using org.json (jar file org.json-20120521.jar). it doesn't look like there's a method called isEmptyObject. =( – Classified Oct 03 '13 at 23:02
@Classified I am not familiar with org.json so this might not be the optimum way. An empty object has no member so therefore method keys() should return iterator with length zero. getJSONObject("problemkey").keys() - check the length of that. – Anderson Oct 03 '13 at 23:13
which library do you use? I found org.json via a google search so I don't know how good/bad it is but it looked fairly popular. http://www.json.org/javadoc/org/json/JSONObject.html. thx again for your responses and help – Classified Oct 03 '13 at 23:20
At the moment Jackson. But this does not mean that org.json is bad, just different. – Anderson Oct 03 '13 at 23:22
1

Another workaround would be to convert your problem value to JSON string and compare it with string "{}". Something like obj.get("dps").toString().equals("{}"). But check what does toString actualy return regarding to whitespaces. – Anderson Oct 03 '13 at 23:27
If the object is a Map then isEmpty() works, but one must first cast to java.util.Map. – Hot Licks Oct 03 '13 at 23:52

score 5 · Answer 5 · answered Oct 03 '13 at 22:40

5

Try:

if (record.has("problemkey") && !record.isNull("problemkey")) {
    // Do something with object.
}

answered Oct 03 '13 at 22:40

Orel Eraki

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thx for the suggestion. when I tried your code, it thinks {} is not null and prints my message, which is not what i want. i dont' know why it thinks {} is not null. – Classified Oct 03 '13 at 22:55

score 2 · Answer 6 · answered Sep 03 '14 at 13:17

I have added isEmpty() methods on JSONObject and JSONArray()

 //on JSONObject 
 public Boolean isEmpty(){         
     return !this.keys().hasNext();
 }

...

//on JSONArray
public Boolean isEmpty(){
    return this.length()==0;        
}

you can get it here https://github.com/kommradHomer/JSON-java

score 2 · Answer 7 · answered Oct 26 '15 at 17:38

2

I would do the following to check for an empty object

obj.similar(new JSONObject())

answered Oct 26 '15 at 17:38

sorjef

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This is actually pretty clever. I wouldn't use it on something so small as this, but it's definitely not an empty-check I had thought of before. – Csteele5 Dec 14 '15 at 04:35

score 2 · Answer 8 · answered Oct 30 '18 at 15:34

if you want to check for the json empty case, we can directly use below code

String jsonString = {};
JSONObject jsonObject = new JSONObject(jsonString);
if(jsonObject.isEmpty()){
 System.out.println("json is empty");
} else{
 System.out.println("json is not empty");
}

this may help you.

score 2 · Answer 9 · answered May 16 '19 at 15:52

2

For this case, I do something like this:

var obj = {};

if(Object.keys(obj).length == 0){
        console.log("The obj is null")
}

answered May 16 '19 at 15:52

rachit7

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score 0 · Answer 10 · answered Oct 03 '13 at 23:53

0

Object getResult = obj.get("dps"); 
if (getResult != null && getResult instanceof java.util.Map && (java.util.Map)getResult.isEmpty()) {
    handleEmptyDps(); 
} 
else {
    handleResult(getResult); 
}

answered Oct 03 '13 at 23:53

Hot Licks

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Sashko · Answer 11 · 2017-03-17T22:01:03.750

0

If JSON returned with following structure when records is an ArrayNode:

{}client 
  records[]

and you want to check if records node has something in it then you can do it using a method size();

if (recordNodes.get(i).size() != 0) {}

edited Mar 17 '17 at 22:01

answered Mar 17 '17 at 18:58

Sashko

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score 0 · Answer 12 · edited Mar 20 '20 at 17:02

0

if (jsonObj != null && jsonObj.length > 0)

To check if a nested JSON object is empty within a JSONObject:

if (!jsonObject.isNull("key") && jsonObject.getJSONObject("key").length() > 0)

edited Mar 20 '20 at 17:02

Max

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answered Apr 03 '17 at 14:00

Bharathi Raja

11

1

Please look at [How do I format my Code blocks?](https://meta.stackoverflow.com/questions/251361/how-do-i-format-my-code-blocks) and then add some explanation to your answer. – Clijsters Apr 03 '17 at 14:10

score 0 · Answer 13 · answered Jan 02 '18 at 19:57

0

@Test
public void emptyJsonParseTest() {
    JsonNode emptyJsonNode = new ObjectMapper().createObjectNode();
    Assert.assertTrue(emptyJsonNode.asText().isEmpty());
}

answered Jan 02 '18 at 19:57

Mikey

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score -2 · Answer 14 · edited Jul 15 '14 at 23:34

-2

Use the following code:

if(json.isNull()!= null){  //returns true only if json is not null

}

edited Jul 15 '14 at 23:34

michaelrmcneill

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answered Jul 15 '14 at 23:21

user3487921

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How would the cast go? – Alexandre Santos Jul 16 '14 at 00:03

score -3 · Answer 15 · answered Oct 03 '13 at 22:42

-3

Try /*string with {}*/ string.trim().equalsIgnoreCase("{}")), maybe there is some extra spaces or something

answered Oct 03 '13 at 22:42

APerson

702
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thx for the suggestion. I checked and there are no extra spaces. =( – Classified Oct 03 '13 at 22:51

How to test if JSON Collection object is empty in Java

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