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.

Scott Tesler · Accepted Answer · 2014-06-09 21:18:09Z

176

obj.length() == 0

is what I would do.

answered Jun 9, 2014 at 21:18

Scott Tesler

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Comments

djechlin · Accepted Answer · 2018-04-17 12:43:21Z

46

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, 2018 at 12:43

answered Oct 4, 2013 at 0:04

djechlin

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4 Comments

ParSa Over a year ago

The best answer

Hamid Araghi Over a year ago

It adds calculation and cpu load and not so good approach.

Jonathan E. Landrum Over a year ago

@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.

Smart Coder Over a year ago

in my case I had to use .equals("[]") as the object itself came as null.

Rohan Lodhi · Accepted Answer · 2018-04-27 10:00:43Z

14

If empty array:

.size() == 0

if empty object:

.length() == 0

answered Apr 27, 2018 at 10:00

Rohan Lodhi

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Comments

Anderson · Accepted Answer · 2013-10-03 22:51:46Z

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 3, 2013 at 22:51

Anderson

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6 Comments

Classified Over a year ago

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. =(

Anderson Over a year ago

@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.

Classified Over a year ago

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. json.org/javadoc/org/json/JSONObject.html. thx again for your responses and help

Anderson Over a year ago

At the moment Jackson. But this does not mean that org.json is bad, just different.

Anderson Over a year ago

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.

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Orel Eraki · Accepted Answer · 2013-10-03 22:40:09Z

5

Try:

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

answered Oct 3, 2013 at 22:40

Orel Eraki

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1 Comment

Classified Over a year ago

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.

rachit7 · Accepted Answer · 2019-05-16 15:52:29Z

3

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, 2019 at 15:52

rachit7

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1 Comment

igraczech Over a year ago

Nice one, but this seems more like JavaScript rather than Java.

kommradHomer · Accepted Answer · 2014-09-03 13:17:03Z

2

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

answered Sep 3, 2014 at 13:17

kommradHomer

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Comments

sorjef · Accepted Answer · 2015-10-26 17:38:09Z

2

I would do the following to check for an empty object

obj.similar(new JSONObject())

answered Oct 26, 2015 at 17:38

sorjef

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1 Comment

Csteele5 Over a year ago

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.

Venkata Naresh Babu · Accepted Answer · 2018-10-30 15:34:31Z

2

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.

answered Oct 30, 2018 at 15:34

Venkata Naresh Babu

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Comments

Hot Licks · Accepted Answer · 2013-10-03 23:53:17Z

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 3, 2013 at 23:53

Hot Licks

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Comments

Sashko · Accepted Answer · 2017-03-17 22:01:03Z

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, 2017 at 22:01

answered Mar 17, 2017 at 18:58

Sashko

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Comments

Mikey · Accepted Answer · 2018-01-02 19:57:53Z

0

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

answered Jan 2, 2018 at 19:57

Mikey

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Comments

Max · Accepted Answer · 2020-03-20 17:02:34Z

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, 2020 at 17:02

Max

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answered Apr 3, 2017 at 14:00

Bharathi Raja

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1 Comment

Clijsters Over a year ago

Please look at How do I format my Code blocks? and then add some explanation to your answer.

guymac · Accepted Answer · 2023-09-12 19:10:24Z

0

javax.json.JsonObject extends Map, so you can use the isEmpty() method of Map.

JsonObject dps = obj.getJsonObject("dps");
if (dps != null && !dps.isEmpty())) ... else ...

answered Sep 12, 2023 at 19:10

guymac

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Comments

crifan · Accepted Answer · 2024-08-07 08:36:54Z

0

Util function code:

import org.json.JSONObject;

    public static boolean isJsonEmpty(JSONObject curJson){
        return (null != curJson) && (0 == curJson.length());
    }

call:

boolean isEmpty = isJsonEmpty(jsonObj);

answered Aug 7, 2024 at 8:36

crifan

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Comments

michaelrmcneill · Accepted Answer · 2014-07-15 23:34:44Z

-2

Use the following code:

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

}

edited Jul 15, 2014 at 23:34

michaelrmcneill

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answered Jul 15, 2014 at 23:21

user3487921

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1 Comment

Alexandre Santos Over a year ago

How would the cast go?

APerson · Accepted Answer · 2013-10-03 22:42:17Z

-3

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

answered Oct 3, 2013 at 22:42

APerson

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1 Comment

Classified Over a year ago

thx for the suggestion. I checked and there are no extra spaces. =(

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