How do you set a value to null with org.json.JSONObject in java?

How do you set a value to null with org.json.JSONObject in java? I can certainly read if a value is null by using isNull - but it seems like when I put null, it just ignores me:

JSONObject o = new JSONObject();
o.put("key",null);
o.isNull("key"); // returns true, buuuut...
o.has("key");    // returns false
o.isNull("somethingIHaventSetAtAll");    // also returns true, unfortunately
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最佳答案

Try to set JSONObject.NULL instead of null:

A sentinel value used to explicitly define a name with no value. Unlike null, names with this value:

  • show up in the names() array
  • show up in the keys() iterator
  • return true for has(String)
  • do not throw on get(String)
  • are included in the encoded JSON string.

This value violates the general contract of equals(Object) by returning true when compared to null. Its toString() method returns "null".

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For me with net.sf.json.JSONObject I need to create a null JSON by

new JSONObject(true)

This is how I get class into groovy:

groovy.grape.Grape.grab(group: "org.kohsuke.stapler", module: "json-lib", version: "2.4-jenkins-2")
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I created this project https://github.com/leonardofel/JSON-java-put-null-fix

To change (or fix), just import the library to your pom.xml

this is how your code will behave:

JSONObject o = new JSONObject();
o.put("key", null);
o.isNull("key"); // returns true
o.has("key"); // returns true
o.isNull("somethingIHaventSetAtAll"); // returns true
o.get("key"); // returns null


o.remove("key");
o.isNull("key"); // returns true
o.has("key"); // returns false
o.isNull("somethingIHaventSetAtAll"); // returns true
o.get("key"); // throws JSONException "key" not found
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Create a Utility Class or if you already have an existing one just create this utility method in it.

 class JsonObjectUtility{
public static Object getJSONObjectValue(Object value)  {
return value == null ? "null" : value;
}
}

then pass all input through this utility before passing it to the JSONObject put method as below: (i will use the code sample in the question)

JSONObject o = new JSONObject();
o.put("key", JsonObjectUtility.getJSONObjectValue(null) );

This shall print a json string as below

{ "key" : null }


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