Java, Parse JSON Objects that I know are null

Question

I have an array of JSON objects. To parse these arrays and store the simply data type values, I have to make assumptions of the key names and store them accordingly.

I also know that sometimes the key's values will be null. example {["promotion":null]} how would I parse this?

If I try to access a key whose value is null, I get a JSONException. Now this makes sense, but even if I do if(myJSObject.getString("promotion")!=null) then I will still get JSON exception when it checks

how would I do a conditional check in my code for null objects so that I can avoid the JSON exception

Possible duplicate: stackoverflow.com/questions/2456078/java-json-null-exception — user180100
– user180100, Commented Sep 21, 2011 at 20:14
the answer wouldn't work for me, I can't just use a hashmap because my objects have more than two values to just store. More like 5 or 6 unique key/value pairs — CQM
– CQM, Commented Sep 21, 2011 at 20:19
Ah, so your JSON would need to look more like [{"key1":val1},{"key2":val2},{"key3":val3}], then iterate through the array of objects. — Drizzt321
– Drizzt321, Commented Sep 21, 2011 at 20:20

Philipp Reichart · Accepted Answer · 2016-11-04 18:14:23Z

19

Use JSONObject.optString(String key) or optString(String key, String default).

Edit: ... or isNull(String key), of course :)

edited Nov 4, 2016 at 18:14

answered Sep 21, 2011 at 20:57

Philipp Reichart

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3 Comments

Philipp Reichart Over a year ago

Also check out the other opt...(key) methods for different data types or the general Object opt(key).

Mixaz Over a year ago

optString("promotion",null) returns "null" (not null!) in my case for {"promotion":null}, which I consider to be strange. Javadoc says that null is returned for missing keys, otherwise conversion is made. Probably it is the reason why I get "null" instead of expected null. Seems that I will have to apply the check isNull(), what I tried to avoid. Bad designed API, you poor javascripters! ))

Philipp Reichart Over a year ago

@Pang Thanks for the ping! json.org stopped hosting javadoc, so here's a link to the source code for org.json.JSONObject: github.com/stleary/JSON-java/blob/master/JSONObject.java

Paaske · Accepted Answer · 2011-09-21 20:54:25Z

1

I think you'll need to format the JSON differently;

for an array of promotions

{promotions:[{promotion:null}, {promotion:5000}]}

for a single promotion

{promotion:null}

edit: depending on which json api you're using, there might be a null check. Google's gson library has an .isJsonNull() method

answered Sep 21, 2011 at 20:54

Paaske

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Comments

Drizzt321 · Accepted Answer · 2011-09-21 20:19:34Z

0

Uh...I don't think that is a properly formatted JSON string. [] indicates an array, which doesn't have any kind of key=>value pairing like an object does. What I think you want would be {"promotion":null}, which then your code snippet likely would work.

answered Sep 21, 2011 at 20:19

Drizzt321

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1 Comment

Drizzt321 Over a year ago

I'm pretty sure JSON array can't have pairs, just values. See json.org. So ["promotion":null] is invalid JSON.

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