Java 使用“键”和“值”属性反序列化 JSON 映射不适用于 Jackson
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时间：2020-08-13 03:40:04 来源:igfitidea点击:
Deserializing JSON map with "key" & "value" properties does not work with Hymanson
提问by joelpet
Questions
问题
- To begin with, does the serialized JSON serialization below make sense?
- If so, why am I not getting the Map back?
- What can I do about it on the deserializing side?
- 首先，下面的序列化 JSON 序列化有意义吗？
- 如果是这样，为什么我没有取回地图？
- 在反序列化方面我能做些什么？
JSON serialization of Map<String, String> property (excerpt):
Map<String, String> 属性的 JSON 序列化（摘录）：
{
"attributes": {
"entry": [
{
"key": "operating system",
"value": "GNU/Linux"
},
{
"key": "allergies",
"value": "weed"
}
]
}
}
POJO for deserialization:
用于反序列化的 POJO：
class Contact implements Comparable<Contact>, Serializable {
@JsonProperty("attributes")
private Map<String, String> attributes;
...
}
Causes this exception:
导致此异常：
Thread-4889 An exception occurred during request network execution :Could not read JSON: Can not deserialize instance of java.lang.String out of START_ARRAY token
at [Source: libcore.net.http.FixedLengthInputStream@43822760; line: 1, column: 17] (through reference chain: com.example.model.Contact["attributes"]); nested exception is com.fasterxml.Hymanson.databind.JsonMappingException: Can not deserialize instance of java.lang.String out of START_ARRAY token
at [Source: libcore.net.http.FixedLengthInputStream@43822760; line: 1, column: 17] (through reference chain: com.example.model.Contact["attributes"])
org.springframework.http.converter.HttpMessageNotReadableException: Could not read JSON: Can not deserialize instance of java.lang.String out of START_ARRAY token
at [Source: libcore.net.http.FixedLengthInputStream@43822760; line: 1, column: 17] (through reference chain: com.example.model.Contact["attributes"]); nested exception is com.fasterxml.Hymanson.databind.JsonMappingException: Can not deserialize instance of java.lang.String out of START_ARRAY token
at [Source: libcore.net.http.FixedLengthInputStream@43822760; line: 1, column: 17] (through reference chain: com.example.model.Contact["attributes"])
at org.springframework.http.converter.json.MappingHymanson2HttpMessageConverter.readInternal(MappingHymanson2HttpMessageConverter.java:126)
at org.springframework.http.converter.AbstractHttpMessageConverter.read(AbstractHttpMessageConverter.java:147)
at org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:76)
at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:484)
at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:439)
at org.springframework.web.client.RestTemplate.getForObject(RestTemplate.java:237)
at com.example.providers.Query.loadDataFromNetwork(Query.java:99)
at com.octo.android.robospice.request.CachedSpiceRequest.loadDataFromNetwork(CachedSpiceRequest.java:45)
at com.octo.android.robospice.request.RequestRunner.processRequest(RequestRunner.java:130)
at com.octo.android.robospice.request.RequestRunner.run(RequestRunner.java:197)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:390)
at java.util.concurrent.FutureTask.run(FutureTask.java:234)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
at java.lang.Thread.run(Thread.java:841)
Caused by: com.fasterxml.Hymanson.databind.JsonMappingException: Can not deserialize instance of java.lang.String out of START_ARRAY token
at [Source: libcore.net.http.FixedLengthInputStream@43822760; line: 1, column: 17] (through reference chain: com.example.model.Contact["attributes"])
at com.fasterxml.Hymanson.databind.DeserializationContext.mappingException(DeserializationContext.java:691)
at com.fasterxml.Hymanson.databind.deser.std.StringDeserializer.deserialize(StringDeserializer.java:46)
at com.fasterxml.Hymanson.databind.deser.std.StringDeserializer.deserialize(StringDeserializer.java:11)
at com.fasterxml.Hymanson.databind.deser.std.MapDeserializer._readAndBindStringMap(MapDeserializer.java:430)
at com.fasterxml.Hymanson.databind.deser.std.MapDeserializer.deserialize(MapDeserializer.java:312)
at com.fasterxml.Hymanson.databind.deser.std.MapDeserializer.deserialize(MapDeserializer.java:26)
at com.fasterxml.Hymanson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:525)
at com.fasterxml.Hymanson.databind.deser.impl.FieldProperty.deserializeAndSet(FieldProperty.java:106)
at com.fasterxml.Hymanson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:242)
at com.fasterxml.Hymanson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:118)
at com.fasterxml.Hymanson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:227)
at com.fasterxml.Hymanson.databind.deser.std.CollectionDeserializer.des
The attributes Object when inspected in debugger after deserialization:
反序列化后在调试器中检查的属性对象：
Further inspection after changing to:
改成后进一步检查：
@JsonProperty("attributes")
private Map<String, List<Map<String, String>>> attributes;
Dependencies:
依赖项：
- com.fasterxml.Hymanson.core:Hymanson-core:2.3.0
- com.fasterxml.Hymanson.core:Hymanson-databind:2.3.0
- com.fasterxml.Hymanson.core:Hymanson-annotations:2.3.0
- com.fasterxml.Hymanson.core:Hymanson-core:2.3.0
- com.fasterxml.Hymanson.core:Hymanson-databind:2.3.0
- com.fasterxml.Hymanson.core:Hymanson-annotations:2.3.0
采纳答案by Maxim Shoustin
If we will convert Mapto json:
如果我们将转换Map为 json：
Map<String, String> map = new HashMap<String, String>();
map.put("operating system", "GNU/Linux");
map.put("allergies", "weed");
The output will be:
输出将是：
{"operating system":"GNU/Linux","allergies":"weed"}
As we can see there is no key/value.
正如我们所见，没有key/value.
Solution
解决方案
WrapperObject
包装对象
@JsonIgnoreProperties(ignoreUnknown = true)
public class WrapperObject { // we can give any name to class, its only external {}
private Attributes attributes;
public WrapperObject() {}
public Attributes getAttributes() {
return attributes;
}
}
Attributes
属性
@JsonIgnoreProperties(ignoreUnknown = true)
public class Attributes {
public Attributes() {}
private ArrayList<Entry> entry;
public ArrayList<Entry> getEntry() {
return entry;
}
}
Entry
入口
@JsonIgnoreProperties(ignoreUnknown = true)
public class Entry {
private String key;
private String value;
public Entry() {}
public String getKey() {
return key;
}
public String getValue() {
return value;
}
}
Launcher
启动器
public static void main(String[] args) throws JsonParseException, JsonMappingException, IOException {
String str = "{" +
" \"attributes\": {" +
" \"entry\": [" +
" {" +
" \"key\": \"operating system\"," +
" \"value\": \"GNU/Linux\"" +
" }," +
" {" +
" \"key\": \"allergies\"," +
" \"value\": \"weed\"" +
" }" +
" ]" +
" }" +
"}";
ObjectMapper mapper = new ObjectMapper();
WrapperObject mj = mapper.readValue(str, WrapperObject.class);
if(mj == null){
System.err.println("null");
}
// dummy check
System.out.println(mj.getAttributes().getEntry().get(0).getKey());
}
Output:
输出：
operating system
