杰克逊不能反序列化空数组
Posted
技术标签:
【中文标题】杰克逊不能反序列化空数组【英文标题】：Jackson Can not deserialize empty array 【发布时间】：2014-09-29 17:42:23 【问题描述】：我正在阅读 Facebook Insights 并试图让 Jackson 将 JSON 映射到 Object。如果所有数据都没有空，我让它工作。但是我在尝试反序列化键值的空数组时遇到问题。即使尝试了这个帖子：How to prevent null values inside a Map and null fields inside a bean from getting serialized through Jackson 也没有解决问题:(
这是 JSON：
"data":["id":"492640667465465\/insights\/page_fans_country\/lifetime","name":"page_fans_country","period":"lifetime","values":["value":"MY":26315,"ID":311,"SG":77,"NP":63,"MM":56,"PH":51,"GB":44,"US":44,"KR":36,"TH":36,"IN":34,"BD":24,"PK":22,"BN":22,"AU":15,"TW":14,"VN":12,"KH":11,"YE":11,"CA":10,"JP":10,"EG":8,"ZA":7,"SA":6,"ES":6,"HK":6,"FR":6,"IT":5,"IL":5,"IR":5,"NG":5,"LK":5,"BR":5,"IQ":4,"AF":4,"AE":4,"GT":4,"RO":4,"LR":4,"RU":4,"PS":4,"DE":4,"CN":4,"LY":3,"JO":3,"end_time":"2014-08-02T07:00:00+0000","value":"MY":26326,"ID":315,"SG":77,"NP":63,"MM":56,"PH":54,"GB":44,"US":43,"TH":38,"KR":36,"IN":33,"BD":23,"BN":22,"PK":21,"AU":16,"TW":14,"VN":12,"KH":11,"YE":11,"CA":10,"JP":10,"EG":8,"ZA":7,"SA":7,"ES":6,"HK":6,"FR":6,"IT":5,"IL":5,"IR":5,"NG":5,"LK":5,"BR":5,"IQ":4,"RU":4,"CN":4,"GT":4,"RO":4,"LR":4,"AF":4,"PS":4,"DE":4,"AE":4,"LY":3,"CH":3,"end_time":"2014-08-03T07:00:00+0000","value":"MY":26338,"ID":312,"SG":79,"NP":63,"MM":55,"PH":52,"US":45,"GB":44,"TH":39,"KR":34,"IN":32,"BD":24,"BN":22,"PK":21,"AU":16,"TW":14,"KH":12,"VN":12,"CA":11,"YE":11,"JP":10,"EG":8,"ZA":7,"SA":7,"ES":6,"HK":6,"FR":6,"IT":5,"CN":5,"IR":5,"NG":5,"LK":5,"BR":5,"IL":5,"IQ":4,"AF":4,"AE":4,"GT":4,"RO":4,"LR":4,"RU":4,"PS":4,"DE":4,"NZ":3,"TR":3,"end_time":"2014-08-04T07:00:00+0000"],"title":"Lifetime Likes by Country","description":"Lifetime: Aggregated Facebook location data, sorted by country, about the people who like your Page. (Unique Users)","id":"492640667465465\/insights\/page_storytellers_by_country\/day","name":"page_storytellers_by_country","period":"day","values":["value":[],"end_time":"2014-08-02T07:00:00+0000","value":[],"end_time":"2014-08-03T07:00:00+0000","value":[],"end_time":"2014-08-04T07:00:00+0000"],"title":"Daily Country: People Talking About This","description":"Daily: The number of People Talking About the Page by user country (Unique Users)","id":"492640667465465\/insights\/page_storytellers_by_country\/week","name":"page_storytellers_by_country","period":"week","values":["value":"MY":136,"IN":3,"ID":2,"BD":1,"US":1,"TN":1,"AU":1,"end_time":"2014-08-02T07:00:00+0000","value":"MY":131,"IN":3,"US":1,"TN":1,"AU":1,"ID":1,"end_time":"2014-08-03T07:00:00+0000","value":"MY":118,"IN":2,"KH":1,"TR":1,"US":1,"TN":1,"AR":1,"AU":1,"end_time":"2014-08-04T07:00:00+0000"],"title":"Weekly Country: People Talking About This","description":"Weekly: The number of People Talking About the Page by user country (Unique Users)","id":"492640667465465\/insights\/page_storytellers_by_country\/days_28","name":"page_storytellers_by_country","period":"days_28","values":["value":"MY":492,"IN":5,"ID":3,"AU":2,"SG":2,"ZA":2,"US":2,"GB":2,"RO":1,"PH":1,"NP":1,"BD":1,"JO":1,"PS":1,"TN":1,"IR":1,"CA":1,"CN":1,"KR":1,"end_time":"2014-08-02T07:00:00+0000","value":"MY":499,"IN":5,"ID":3,"GB":2,"SG":2,"ZA":2,"US":2,"RO":1,"PH":1,"NP":1,"BD":1,"AU":1,"CN":1,"KR":1,"TN":1,"IR":1,"CA":1,"JO":1,"end_time":"2014-08-03T07:00:00+0000","value":"MY":501,"IN":4,"ID":3,"SG":2,"ZA":2,"US":2,"GB":2,"AU":1,"RO":1,"PH":1,"NP":1,"JO":1,"AR":1,"KR":1,"BD":1,"TR":1,"IR":1,"CA":1,"CN":1,"KH":1,"TN":1,"end_time":"2014-08-04T07:00:00+0000"],"title":"28 Days Country: People Talking About This","description":"28 Days: The number of People Talking About the Page by user country (Unique Users)"],"paging":"previous":"https:\/\/graph.facebook.com\/v2.0\/492640667465465\/insights?since=1406649169&until=1406908369","next":"https:\/\/graph.facebook.com\/v2.0\/492640667465465\/insights?since=1407167569&until=1407426769"
我当前的代码根本不喜欢这样 --> "value":[]
以下是我的对象：
import java.util.Date;
import java.util.List;
import java.util.Map;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonInclude.Include;
public class Insights
private Data[] data;
private Paging paging;
public Data[] getData()
return data;
public void setData(Data[] data)
this.data = data;
public Paging getPaging()
return paging;
public void setPaging(Paging paging)
this.paging = paging;
/**
* inner class for Data
* @author pohsoon.yap
*
*/
public static class Data
private String id;
private String name;
private String period;
private Values[] values;
private String title;
private String description;
public String getId()
return id;
public void setId(String id)
this.id = id;
public String getName()
return name;
public void setName(String name)
this.name = name;
public String getPeriod()
return period;
public void setPeriod(String period)
this.period = period;
public Values[] getValues()
return values;
public void setValues(Values[] values)
this.values = values;
public String getTitle()
return title;
public void setTitle(String title)
this.title = title;
public String getDescription()
return description;
public void setDescription(String description)
this.description = description;
/**
* inner class for Values
* @author pohsoon.yap
*
*/
public static class Values
// if "value":[] then this will break
private Map<String, Integer> Value;
private String end_time;
public Map<String, Integer> getValue()
return Value;
public void setValue(Map<String, Integer> value)
Value = value;
public String getEnd_time()
return end_time;
public void setEnd_time(String end_time)
this.end_time = end_time;
public static class Paging
private String previous;
private String next;
public String getPrevious()
return previous;
public void setPrevious(String previous)
this.previous = previous;
public String getNext()
return next;
public void setNext(String next)
this.next = next;
我的代码sn-p如下：
ObjectMapper mapper = new ObjectMapper();
mapper.setSerializationInclusion(JsonInclude.Include.NON_EMPTY);
List<Insights> insightList = new ArrayList();
String insightStr = "";
try
for (Operation operation : mq.getOperationList())
String apiEndPoint = this.facebookGraphApiUrl + operation.getApi();
apiEndPoint = apiEndPoint.replace("pageid", mq.getFacebookPage().getPageId());
uri = new URI(apiEndPoint);
insightStr = facebook.getApi().restOperations().getForObject(uri, String.class);
Insights insights = mapper.readValue(insightStr, Insights.class);
完整的堆栈跟踪：
com.fasterxml.jackson.databind.JsonMappingException：无法从 START_ARRAY 令牌中反序列化 java.util.LinkedHashMap 的实例 在 [来源：java.io.StringReader@625a80df;行：1，列：1603]（通过参考链：com.social.facebook.model.Insights["data"]->com.social.facebook.model.Data["values"]->com.social.facebook .model.Values["value"]) 在 com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:164) 在 com.fasterxml.jackson.databind.DeserializationContext.mappingException（DeserializationContext.java:599） 在 com.fasterxml.jackson.databind.DeserializationContext.mappingException（DeserializationContext.java:593） 在 com.fasterxml.jackson.databind.deser.std.MapDeserializer.deserialize(MapDeserializer.java:306) 在 com.fasterxml.jackson.databind.deser.std.MapDeserializer.deserialize(MapDeserializer.java:26) 在 com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:375) 在 com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:98) 在 com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:308) 在 com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:121) 在 com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:147) 在 com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:18) 在 com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:375) 在 com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:98) 在 com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:308) 在 com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:121) 在 com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:147) 在 com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:18) 在 com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:375) 在 com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:98) 在 com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:308) 在 com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:121) 在 com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2796) 在 com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:1942)
【问题讨论】：
JSON value 属性似乎是一个数组类型，但您的模型类需要一个映射。我想知道 value 属性不为空时的样子？ @AlexeyGavrilov 在我上面附加的同一个 JSON 中，“数据”数组有 4 个项目，其中只有一个项目的值为空，其余的看起来像这样：“值”：“ MY":26315,"ID":311 我认为是一张地图；一个键和一个值？ 【参考方案1】：正如其他人所解释的，您正在尝试将 JSON Array 映射到 Java Map，这是默认情况下不允许的。
但可能允许空 JSON 数组映射到 java.util.Map。通过启用DeserializationFeature.ACCEPT_EMPTY_ARRAY_AS_NULL_OBJECT:
objectMapper.enable(DeserializationFeature.ACCEPT_EMPTY_ARRAY_AS_NULL_OBJECT);
这至少在 POJO 类型的情况下有效；我不记得这是否适用于通常采用 JSON 对象的其他 Java 类型。
【讨论】：
【参考方案2】：模型中的value 字段声明为Map，而相应的JSON 属性可以是空数组或键值映射。 Jackson 无法将空数组分配给地图字段。
假设您希望在客户端解决问题，您可以修改setValue 方法以接受泛型Object，然后验证它是映射还是数组（实际上是List，因为Jackson 反序列化数组作为 Java 集合）。这是一个例子：
public class JacksonArrayAsMap
public static class Bean
private Map<String, Object> value;
public void setValue(Object value)
if (value instanceof Map)
this.value = (Map<String, Object>) value;
else if (value instanceof List && ((List) value).size() == 0)
this.value = Collections.EMPTY_MAP;
else
throw new IllegalArgumentException("Invalid value: " + value);
@Override
public String toString()
return "Bean" +
"value=" + value +
'';
public static void main(String[] args) throws IOException
final String json1 = "\"value\":";
final String json2 = "\"value\":[]";
final String json3 = "\"value\":\"a\":\"b\"";
ObjectMapper mapper = new ObjectMapper();
System.out.println(mapper.readValue(json1, Bean.class));
System.out.println(mapper.readValue(json2, Bean.class));
System.out.println(mapper.readValue(json3, Bean.class));
输出：
Beanvalue=
Beanvalue=
Beanvalue=a=b
【讨论】：
感谢您的回答，我戴上我的爱好帽后会试试这个:) 耶！确认它有效 :) 我将继续处理来自 Graph API 的其他可用 JSON 提要。以上是关于杰克逊不能反序列化空数组的主要内容，如果未能解决你的问题，请参考以下文章