Detecting duplicate entries in a JSON list of objects

Question

I have a JSON file being parsed in java. It has several lists of objects like the following:

{
    "phoneNumbers": [
        {
            "type": "home",
            "number": "212 555-1234"
        },
        {
            "type": "home",
            "number": "212 555-1234"
        },
        {
            "type": "fax",
            "number": "646 555-4567"
        }
    ]
}

It's a sensitive input file and overwriting duplicate entries is not an option. The program checks for duplicates using a for loop and maps when processing a particular list, but I want to check the entire file for dups in one go as the file is being parsed so that in case of error the program stops before running anything else.

I was wondering if there's a JSON parser for java out there that will detect duplicate object entries in the list and provide a message. Also, are there any parsers that will let you know if a declared object gets overwritten because another object with the same name is declared in the same file?

thkala · Accepted Answer · 2014-05-21 23:42:03Z

1

Well, Jackson does have a deserialization feature in its data binding extension that will do what you need: FAIL_ON_READING_DUP_TREE_KEY will cause the parser to fail on reading a duplicate key.

That said, you can probably implement the same functionality for any parser that supports deserializing into custom objects by using a custom Map class that throws an exception if a duplicate key is encountered, rather than just update the value...

As for finding duplicate entries in the list, how about deserializing into a custom LinkedHashSet subclass that throws an exception if a duplicate entry is inserted?

answered May 21, 2014 at 23:42

thkala

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1 Comment

Alex Over a year ago

Thanks this helps! For checking duplicates in arrays I found a json schema validation keyword called uniqueItems, and it seems to work properly.

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