Json Mapping Exception无法从START_ARRAY令牌中反序列化实例

我正在尝试将json请求解析为模型。我不知道这段代码有什么问题。json的语法看起来正确，并且在Java模型上也有注释。我不知道为什么会出现如下错误：

Caused by: org.codehaus.jackson.map.JsonMappingException: Can not deserialize instance of ParametersType out of START_ARRAY token
(through reference chain: Document["parameters"])

Java模型：

@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;

....}

杰森代码：

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