Json Mapping Exception can not deserialize instance out of START_ARRAY token

Question

I'm trying to parse my json request to my model. I don't know, what is wrong in this code. Syntax of json looks correct and annotations on Java model also. I don't know why I'm getting error like: ``` Caused by: org.codehaus.jackson.map.JsonMappingException: Can not deserialize instance of ParametersType out of START_ARRAY token (through reference chain: Document["parameters"]) ``` Java model: ``` @JsonIgnoreProperties( ignoreUnknown = true ) public class Document { @XmlElement( required = true ) @JsonProperty( "templateId" ) protected String templateId; @JsonProperty( "parameters" ) @XmlElement( required = true ) protected ParametersType parameters; @JsonProperty( "documentFormat" ) @XmlElement( required = true ) protected DocumentFormatType documentFormat; ...} @JsonIgnoreProperties( ignoreUnknown = true ) public class ParametersType { @JsonProperty( "parameter" ) protected List<ParameterType> parameter; ...} @JsonIgnoreProperties( ignoreUnknown = true ) public class ParameterType {…

Accepted Answer

You have declared `parameters` as a single object, but you are returning it as an array of multiple objects in your JSON document.

Your model currently defines the parameters node as a `ParametersType` object:

```
@JsonProperty( "parameters" )
@XmlElement( required = true )
protected ParametersType parameters;
```

This means your model object is expecting a JSON document that looks like the following:

```
{
    "templateId": "123",
    "parameters": {
            "parameter": [
                {
                    "key": "id",
                    "value": "1",
                    "type": "STRING_TYPE"
                },
                {
                    "key": "id2",
                    "value": "12",
                    "type": "STRING_TYPE"
                }
            ]
        },
    "documentFormat": "PDF"
}
```

But in your JSON document you are returning an array of `ParametersType` objects. So you need to change your model to be a list of ParametersType objects:

```
@JsonProperty( "parameters" )
@XmlElement( required = true )
protected List<ParametersType> parameters;
```

The fact that you are returning an array of ParametersType objects is why the parser is complaining about not being able to deserialize an object out of START_ARRAY. It was looking for a node with a single object, but found an array of objects in your JSON.

Json Mapping Exception can not deserialize instance out of START_ARRAY token

Solution

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