Json parser to catch trailing commas in Java?

Question

I was using the following to check if a json file was valid:

JsonParser parser = new JsonParser();   
parser.parse(new String(Files.readAllBytes(Paths.get((filePath.toString())))));

But the json file I am validating has trailing commas like below that it doesn't throw an exception for:

"file":"hello.htm"},]

Since this is the last attribute the comma isn't needed and is causing trouble in other areas of our application. Is there a parser or some way to catch this trailing comma?

Good option could be removing these commas before validation, look this for more details stackoverflow.com/questions/34344328/… — gevorg
– gevorg, Commented Jun 22, 2016 at 20:04

Sotirios Delimanolis · Accepted Answer · 2016-06-22 20:25:17Z

2

Assuming JsonParser is part of Gson, you're currently out of luck. Gson's parsing currently interprets the trailing comma in a JSON array as a null value. It's wrong and a resolution seems to be planned for Gson 3.

In the meantime, you can use a different parsing library. I suggest Jackson. If you're just validating the JSON, you can use

ObjectMapper mapper = new ObjectMapper();
mapper.readTree(Files.readAllBytes(Paths.get(filePath.toString())));

This will throw an exception, with a message similar to

Unexpected character (']' (code 93)): expected a value

indicating that it expected an actual value after the ,, not the closing array symbol.

answered Jun 22, 2016 at 20:25

Sotirios Delimanolis

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1 Comment

algrid Over a year ago

Sadly Gson devs are not willing to fix this(

diegomercado · Accepted Answer · 2019-06-17 19:56:41Z

-1

When iterating the JSONArray, you could ask if the element is null:

for (i in 0 until jsonArray.length()) {
    if (!jsonArray.isNull(i)) {
        // parse here...
    }
}

And then you would be able to avoid the 'org.json.JSONException' exception.

answered Jun 17, 2019 at 19:56

diegomercado

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