Question

I created a servlet which responds to get requests with a byte array created from json data. I am trying to consume this data in iOS and use NSJSONSerialization to parse it into a NSDictionary, but it fails with the following error

Error Domain=NSCocoaErrorDomain Code=3840 “The operation couldn’t be completed. (Cocoa error 3840.)” (Duplicate key for object around character 11.) UserInfo=0x6833200 {NSDebugDescription=Duplicate key for object around character 11.}

Here is my code:

NSString *query = @"http://localhost:8888/url?method=retrieve";

NSData *jsonData = [NSData dataWithContentsOfURL:[NSURL URLWithString:query]];
NSError *error = nil;
NSString *stringData = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
NSLog(@"substring to index 255: %@",  [stringData substringToIndex:255]);
NSDictionary *results = jsonData ? [NSJSONSerialization JSONObjectWithData:[stringData dataUsingEncoding:NSUTF8StringEncoding] options:kNilOptions error:&error] : nil;
NSLog(@"Response as Dictionary:\n%@", results.description);
if (error) {
    NSLog(@"Error: %@", error);
}

the value of stringData is

{“APPEALS”:{“APPEAL”:{“AppealID”:387423483,”LastEdit”:”1 . . .

Response as Dictionary returns (null) obviously since there is an error
I am guessing that it has something to do with the fact that my server sends the data in an output stream as a byte[] (java) and it is not formatted correctly as json when received in iOS, but it doesn’t make sense to me why it would fail at character 11 “:”
FYI, the server is written on Google App Engine in java and the localhost url is the local dev server. The json data was created using Jackson Generator library. Thanks!

Answer 1

I discovered the answer myself: when the error points to a duplicate key at a “:” character, that means that some key within the following json array is duplicated, not necessarily the one immediately following that character index. From my json data above, I had many “APPEAL” entries, that when turned into an NSDictionary will throw an error since there can be only 1 value for a given key. I believe my confusion arose from reading a Jackson json generator tutorial which described creating entries with the same key so that they can later be serialized into many instances of an object with “key” as the object class name (so I could have created many APPEAL objects using a Jackson parser, but not so in NSJSONSerialization).

I also had concatenated several json files server side:

( {“table”:{“title”:value}}{“anotherTable”:{“title”:value}} )

so that my url request response could serve several files with 1 request (cost efficiency), but these had to be split client side and serialized individually since “}}{” isn’t legal json format.