Java Json 映射异常无法从 START_ARRAY 令牌反序列化实例

Json Mapping Exception can not deserialize instance out of START_ARRAY token

提问by Marcin Erbel

I'm trying to parse my json request to my model. I dunno 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:

我正在尝试将我的 json 请求解析到我的模型。我不知道这段代码有什么问题。json 的语法看起来正确，Java 模型上的注释也正确。我不知道为什么我会收到如下错误：

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

Java model:

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;

....}

Json code:

json代码：

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

采纳答案by gregwhitaker

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

您已声明parameters为单个对象，但您将其作为 JSON 文档中多个对象的数组返回。

Your model currently defines the parameters node as a ParametersTypeobject:

您的模型当前将参数节点定义为ParametersType对象：

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

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

这意味着您的模型对象需要一个如下所示的 JSON 文档：

{
    "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 ParametersTypeobjects. So you need to change your model to be a list of ParametersType objects:

但是在您的 JSON 文档中，您将返回一个ParametersType对象数组。因此，您需要将模型更改为 ParametersType 对象列表：

@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.

您正在返回一个 ParametersType 对象数组的事实是解析器抱怨无法从 START_ARRAY 反序列化对象的原因。它正在寻找具有单个对象的节点，但在您的 JSON 中找到了一组对象。