Java – JSON mapping exception cannot deserialize an instance to start_ Array token

I tried to parse my JSON request to my model I don't know what's wrong with this code The syntax of JSON is also correct and annotated for the Java model I don't know why I received an error:

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 {

    @XmlElement( required = true )
    @JsonProperty( "key" )
    protected String key;

    @XmlElement( required = true )
    @JsonProperty( "value" )
    @XmlSchemaType( name = "anySimpleType" )
    protected Object value;

    @JsonProperty( "type" )
    @XmlElement( required = true,defaultValue = "STRING_TYPE" )
    protected ParamType type;

Jason Code:

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

Solution

You declare a parameter as a single object, but you return it as an array of multiple objects in a JSON document

Your model currently defines parameter nodes as parameterstype objects:

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

This means that your model object expects a JSON document, as follows:

{
    "templateId": "123","parameters": {
            "parameter": [
                {
                    "key": "id","type": "STRING_TYPE"
                }
            ]
        },"documentFormat": "PDF"
}

But in your JSON document, you returned an array of parameterstype objects Therefore, you need to change the model to the list of parameterstype objects:

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

In fact, you return an array of parameterstype objects is why the parser complains that it cannot deserialize an object at start_ Outside array It was looking for a node with a single object, but found an array of objects in JSON