[英]JSON parse error: Cannot construct instance of `com.tess4j.rest.model.Image` (although at least one Creator exists):
[英]"JSON parse error: Cannot construct instance of (although at least one Creator exists): cannot deserialize from Object value - SpringBoot
我正在將 SpringBoot 與 Mongo 數據庫一起使用,並且我正在嘗試將嵌入式文檔保存到數據庫中。
我有這個 model:
型材.java
@Data
@Document
public class Profile {
public final City city;
public final String imageId;
public Profile(City city,
String imageId) {
this.city = city;
this.imageId = imageId;
}
@Override
public String toString() {
return "Profile{" +
", city=" + city +
", imageId='" + imageId + '\'' +
'}';
}
private static boolean atLeast(int numChars, String s) {
if (s == null) {
return false;
}
var str = s.strip();
return str.length() >= numChars;
}
public static ProfileBuilder builder() {
return new ProfileBuilder();
}
public static final class ProfileBuilder {
public City city;
public String imageId;
private ProfileBuilder() {
}
public ProfileBuilder withCity(City city) {
this.city = city;
return this;
}
public ProfileBuilder withImageId(String imageId) {
this.imageId = imageId;
return this;
}
public Profile build(){
return new Profile(city, imageId);
}
}
}
城市.java
public class City {
public final String name;
public City(String name) {
this.name = name;
}
@Override
public String toString() {
return "City{" +
", name='" + name + '\'' +
'}';
}
}
ProfileController.java
@RequestMapping( method = RequestMethod.POST)
public Profile addUser(@RequestBody Profile profile) {
return profileService.addProfile(profile);
}
和 postman 我發送這個 JSON
{
"city":{
"name":"Atena"
},
"imageId" : "Doe",
}
}
但我收到以下錯誤:
"JSON parse error: Cannot construct instance of `domain.City` (although at least one Creator exists): cannot deserialize from Object value (no delegate- or property-based Creator);"
至少有兩種解決方案。
@JsonCreator
添加到構造函數並將@JsonProperty
添加到其參數(以指示 Jackson 如何以正確的順序將 JSON 項替換到構造函數中)class Profile {
...
@JsonCreator
public Profile(@JsonProperty("city") City city,
@JsonProperty("imageId") String imageId) {
this.city = city;
this.imageId = imageId;
}
...
}
(+ 城市類相同)
final
類屬性並提供默認的無參數構造函數(以及現有的全參數構造函數)。class Profile {
public City city;
public String imageId;
public Profile() {
}
public Profile(City city, String imageId) {
this.city = city;
this.imageId = imageId;
}
}
(+ 城市類相同)
測試
class Test {
public static void main(String[] args) throws JsonProcessingException {
String json = "{\"city\":{\"name\":\"Atena\"},\"imageId\":\"Doe\"}";
Profile p = new ObjectMapper().readValue(json, Profile.class);
System.out.println(p);
}
}
輸出:
Profile{, city=City{, name='Atena'}, imageId='Doe'}
在只有一個屬性的類中,要反序列化 object Json 需要來自該 class 的 nos 參數構造函數。
在您的 class 城市中,您需要一個 nos arg 構造函數,將其添加到您需要的 class 中:
public City () {}
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