CODEWITHSUNDEEP
javajsonspring-bootspring-data-jpajackson-databind
user13226270
user13226270

Reputation:

com.fasterxml.jackson.databind.exc.MismatchedInputException: Can not deserialize instance of object out of START_ARRAY token - JAVA

Getting the MismatchedInputException. Searched a lot of questions here but havent found a solution yet.

Code:

import /path/to/file/Bars;
List<Bars> barResults = null;
public boolean validateData() throws IOException {
        boolean flag = false;
        try {
            if (Data.read() != -1) {
                BufferedReader reader = new BufferedReader(new InputStreamReader(Data));
                String line;
                while ((line = reader.readLine()) != null) {
                    line = "[{" + line;
                    System.out.println(line);
                    ObjectMapper om = new ObjectMapper().configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
                    Bars ms = om.readValue(line, Bars.class);
                    System.out.println(ms);
                    break;
                }
                reader.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return flag;
    }

Json: //shorten for example

[{"createdOn":1601058721310,"lastUpdated":null,"lastUpdatedBy":null,"createdBy":null,"appId":null,"logical":"N","calculationDateTime":1601058721310,"mtaVersionNumber":null,"storageRegionName":"texas","createdOnDate":1601058721310,"lastUpdatedDate":0}]

Output:

[{"createdOn":1601058721310,"lastUpdated":null,"lastUpdatedBy":null,"createdBy":null,"appId":null,"logical":"N","calculationDateTime":1601058721310,"mtaVersionNumber":null,"storageRegionName":"texas","createdOnDate":1601058721310,"lastUpdatedDate":0}]
com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `object` out of START_ARRAY token
 at [Source: (StringReader); line: 1, column: 1]

I am not sure what is causing this exception. When I start the application, i runs and reads the JSON fine..but throws exception.

Upvotes: 0

Views: 1838

Answers (1)

gabeg
gabeg

Reputation: 139

In your call to readValue you are passing Bars.class as the second argument, which tells Jackson that the first argument (line) is a JSON representation of a Bars instance and that's what it should return.

JSON objects start with a {, and because you've asked Jackson to deserialize an object, it expects the input to start with a {. But the JSON that you're passing in, line, isn't a Bars instance: it's an array containing a Bars instance, and it starts with a [.

So it throws an error message that says "I was told an object would be here, but instead I found the start of an array".

To fix it, you can either ask Jackson to deserialize an array of "Bar" objects by changing the second argument of readValue to Bars[].class and then extract the bar instance from the array, or you could stop adding a "[" to the start of the line and chop the "]" off the end of it so that it's just a single object and not an array containing that single object.

Upvotes: 1

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