How do I create a JSON Array?

Question

Hi I want to create a JSON array.

I have tried using:

JSONArray jArray = new JSONArray();
  while(itr.hasNext()){
    int objId = itr.next();
jArray.put(objId, odao.getObjectName(objId));
  }
results = jArray.toString();

Note: odao.getObjectName(objId) retrieves a name based on the "object Id" which is called objId.

However I get a very funny looking array like

[null,null,null,"SomeValue",null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,"AnotherValue",null,null,null,null,null,null,null,null,null,null,"SomethingElse","AnotherOne","LastOne"]

With only "LastOne" being displayed when I retrieve it using jQuery.

The Array SHould look like

{["3":"SomeValue"],["40":"AnotherValue"],["23":"SomethingElse"],["9":"AnotherOne"],["1":"LastOne"]}

The numbers aren't showing up at all for some reason in the array that I am getting.

Whatever you get, it shouldn't look like that. Arrays are [foo,bar,baz] while objects are { "foo": "value", "bar": "value", "baz": "value" }. You seem to have your {} and [] confused. — Quentin
– Quentin, Commented Mar 30, 2010 at 9:41
Thanks everyone, I got something from each answer. In the end I realised my question wasn't expressed exactly as it should have been, but your answers solved my problem. — Ankur
– Ankur, Commented Mar 30, 2010 at 13:32

Community · Accepted Answer · 2017-05-23 11:52:56Z

12

For your quick Solution:

JSONArray jArray = new JSONArray();
while (itr.hasNext()) {
   JSONObject json = new JSONObject();
   int objId = itr.next();
   json.put(Integer.toString(objId), odao.getObjectName(objId));
   jArray.put(json);
}

results = jArray.toString();

Based on T. J. Crowder's response, my solution does this:

[{"3":"SomeValue"},
 {"40":"AnotherValue"},
 {"23":"SomethingElse"},
 {"9":"AnotherOne"},
 {"1":"LastOne"}
]

Refer to Jim Blackler's comment of what you're doing wrong.

edited May 23, 2017 at 11:52

CommunityBot

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answered Mar 30, 2010 at 9:45

Buhake Sindi

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Comments

Jim Blackler · Accepted Answer · 2010-03-30 09:37:22Z

8

The clue is in the documentation for JSONArray for method put(int index, String value)

If the index is greater than the length of the JSONArray, then null elements will be added as necessary to pad it out.

answered Mar 30, 2010 at 9:37

Jim Blackler

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2 Comments

Ankur Over a year ago

I see so the index is literally the index of the Array and not some value I can assign.

T.J. Crowder Over a year ago

@Ankur: Yes, it's an array in the numerically-index-array sense, not a map (aka dictionary aka associative array). You can use JSONObject (json.org/javadoc/org/json/JSONObject.html) for a map; the keys in JSON objects are always strings, so you'll need to make a string out of your objId, but that's easy enough.

Community · Accepted Answer · 2017-05-23 12:01:09Z

2

What you've quoted for your "The object should look like" is invalid JSON. It's an object (delimited by { and }) but then it has values within it that don't have any keys. See json.org for the syntax of JSON.

If you want this:

{"3":"SomeValue",
 "40":"AnotherValue",
 "23":"SomethingElse",
 "9":"AnotherOne",
 "1":"LastOne"
}

...use JSONObject instead, and turn your objIds into keys when putting the entries in, e.g.:

JSONObject obj = new JSONObject();
while(itr.hasNext()){
    int objId = itr.next();
    obj.put(String.valueOf(objId), odao.getObjectName(objId));
}
results = obj.toString();

If you want this:

[{"3":"SomeValue"},
 {"40":"AnotherValue"},
 {"23":"SomethingElse"},
 {"9":"AnotherOne"},
 {"1":"LastOne"}
]

...see The Elite Gentleman's answer (that's a JSONArray of JSONObjects).

edited May 23, 2017 at 12:01

CommunityBot

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answered Mar 30, 2010 at 9:50

T.J. Crowder

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1 Comment

Buhake Sindi Over a year ago

Until we know what he/she really wants, every answer here is correct.

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