杰克逊 - JsonMappingException由于构造函数 [英] Jackson - JsonMappingException due to constructor
问题描述
在尝试反序列化JSON时遇到以下异常
$ b blockquote>
找不到适用于类型的合适构造函数[简单类型，类MyObj $ obj $ Card]：不能从JSON对象实例化（需要添加/启用类型信息？）at [Source：java.io.StringReader @ 4344ee21;第1行，第201列] （通过引用链： MyObj [obj] - > Obj [cards] ）
而JSON是
{
obj：{
api：OK，
cache：false，
cards：[
{
id：1232995897，
items：[
{
id：vmdSJLpnY，
cat：50，
rating： 0.0
}
]
}，
{
id：0005897，
items：[
{
id：vxdSJLpnY，
cat：50，
rating：0.0
}
]
}
]
在 Obj $ j
$ b $ p $ j $'
产生上述例外。将类型 Card [] 更改为 Object [] 不会产生异常，但它缺少正确的映射I希望得到。
任何线索我该如何解决它？一个片段将是伟大的！
这个错误意味着什么？
更新
包括Java类。
import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.google.gson.Gson;
@JsonIgnoreProperties（ignoreUnknown = true）
public final class MyObj {
@JsonIgnoreProperties（ignoreUnknown = true）
public final class Obj {
@JsonIgnoreProperties （ignoreUnknown = true）
public final class Card {
@JsonIgnoreProperties（ignoreUnknown = true）
public final class Item {
@JsonProperty（id）private String id;
@JsonProperty（猫）private String cat;
@JsonProperty（评级）私人字符串评分;
public final String getId（）{return id; }
public final String getCat（）{return cat; }
public final String getRating（）{return ranting; }
public final String toString（）{return new Gson（）。toJson（this）; }
}
@JsonProperty（items）private Item [] items;
public final Item [] getItems（）{return items; }
public final String toString（）{return new Gson（）。toJson（this）; }
}
@JsonProperty（卡）私人卡[]卡;
public card [] getCards（）{return cards; }
public final String toString（）{return new Gson（）。toJson（this）; }
}
@JsonProperty（obj）MyObj obj;
public final Card [] getCards（）{return apiServiceResultsNoLists.getCards（）; }
}
我认为问题是很可能是卡对象
$ b 编辑 strong>
我有两件事：
*你没有setter。
*你没有一个公共构造函数可以设置你的文件。
$ b解决方案：
- >将公共setter添加到类
- >或创建用@JsonCreator注释的参数化构造函数
<当然，解析器可以做到反射式的mofidy the visibility技巧，但是，它并不是它应该被播放的方式。
EDIT2
我认为这应该可行，但我无法测试它 - 我现在没有一个与杰克逊正确设置的项目（这只是它的一部分，但我认为很容易理解我想要展示的内容）注意，我将数组更改为List：
@JsonIgnoreProperties（ignoreUnknown = true）
public final class Card {
@JsonIgnoreProperties（ignoreUnknown = true）
public final class Item {
@JsonProperty（id ）私人字符串ID;
@JsonProperty（猫）private String cat;
@JsonProperty（评级）私人字符串评分;
@JsonCreator
public Item（@JsonProperty（id）字符串id，@JsonProperty（cat）字符串cat，@JsonProperty（rating）字符串等级）{
this.id = id;
this.cat = cat;
this.rating = rating;
}
public final String getId（）{return id; }
public final String getCat（）{return cat; }
public final String getRating（）{return ranting; }
public final String toString（）{return new Gson（）。toJson（this）; }
}
@JsonProperty（items）private List< Item>项目;
@JsonCreator
公共卡（@JsonProperty（items）List< Item> items）{
this.items = items;
}
public final List< Item> getItems（）{返回项目; }
$ b $ public final String toString（）{return new Gson（）。toJson（this）; }
}
I am having the following exception when trying to deserialize a JSON
No suitable constructor found for type
[simple type, class MyObj$obj$Card]:can not instantiate from JSON object (need to add/enable type information?) at[Source: java.io.StringReader@4344ee21; line: 1, column: 201](through reference chain:MyObj["obj"]->Obj["cards"])
And the JSON is
{
"obj":{
"api":"OK",
"cache":false,
"cards":[
{
"id":1232995897,
"items":[
{
"id":"vmdSJLpnY",
"cat":50,
"rating":0.0
}
]
},
{
"id":0005897,
"items":[
{
"id":"vxdSJLpnY",
"cat":50,
"rating":0.0
}
]
}
]
}
}
And within the Obj class I have the following statement
@JsonProperty("cards") private Card[] cards;
Which produces the exception above. Changing the type Card[] to Object[] does not produce an exception, but it lacks of the correct mapping I desire to get.
Any clue how can I resolve it? A snippet will be GREAT! What this error means anyhow?
UPDATE
I have included the Java class.
import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.google.gson.Gson;
@JsonIgnoreProperties(ignoreUnknown=true)
public final class MyObj {
@JsonIgnoreProperties(ignoreUnknown=true)
public final class Obj {
@JsonIgnoreProperties(ignoreUnknown=true)
public final class Card {
@JsonIgnoreProperties(ignoreUnknown=true)
public final class Item {
@JsonProperty("id") private String id;
@JsonProperty("cat") private String cat;
@JsonProperty("rating") private String rating;
public final String getId() { return id; }
public final String getCat() { return cat; }
public final String getRating() { return ranting; }
public final String toString() { return new Gson().toJson(this); }
}
@JsonProperty("items") private Item[] items;
public final Item[] getItems() { return items; }
public final String toString() { return new Gson().toJson(this); }
}
@JsonProperty("cards") private Card[] cards;
public Card[] getCards() { return cards; }
public final String toString() { return new Gson().toJson(this); }
}
@JsonProperty("obj") MyObj obj;
public final Card[] getCards(){ return apiServiceResultsNoLists.getCards(); }
}
I think the problem is most likely with the Card object
- it might not have a default constructor
- if it doesn't have a default constructor, it should be annotated using @JsonCreator
EDIT
I have two things:
* you don't have setters.
* you don't have a public constructor that would be allowed to set your fileds.
How should the deserializer populate your fields if you don't give it any (legal*) means for it?
Solutions:
-> add public setters to the classes
-> or create parametrized constructors annotated with @JsonCreator
*: of course, the parser could do the reflective "mofidy the visibility" trick, but come on, this is not "the way it's meant to be played"
EDIT2 I think this should work, but I can't test it - I don't have a project at hand with Jackson properly set up now (this is just a part of it, but I think it is easy to interpret what I wanted to show.) Note, I changed the array to a List:
@JsonIgnoreProperties(ignoreUnknown=true)
public final class Card {
@JsonIgnoreProperties(ignoreUnknown=true)
public final class Item {
@JsonProperty("id") private String id;
@JsonProperty("cat") private String cat;
@JsonProperty("rating") private String rating;
@JsonCreator
public Item(@JsonProperty("id") String id, @JsonProperty("cat") String cat, @JsonProperty("rating") String rating) {
this.id = id;
this.cat = cat;
this.rating = rating;
}
public final String getId() { return id; }
public final String getCat() { return cat; }
public final String getRating() { return ranting; }
public final String toString() { return new Gson().toJson(this); }
}
@JsonProperty("items") private List<Item> items;
@JsonCreator
public Card(@JsonProperty("items") List<Item> items) {
this.items = items;
}
public final List<Item> getItems() { return items; }
public final String toString() { return new Gson().toJson(this); }
}
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