Reason:
This error occurs because Jackson Library doesn't know how to create your model which doesn't have an empty constructor and the model contains a constructor with parameters that didn't annotate its parameters with @JsonProperty("field_name"). By default Java compiler creates an empty constructor if you didn't add a constructor to your class.
Solution:
Add an empty constructor to your model or annotate constructor parameters with @JsonProperty("field_name")
If you use a Kotlin data class then also can annotate with @JsonProperty("field_name") or register jackson module kotlin to ObjectMapper.
You can create your models using http://www.jsonschema2pojo.org/.
Answer from Bek on Stack OverflowReason:
This error occurs because Jackson Library doesn't know how to create your model which doesn't have an empty constructor and the model contains a constructor with parameters that didn't annotate its parameters with @JsonProperty("field_name"). By default Java compiler creates an empty constructor if you didn't add a constructor to your class.
Solution:
Add an empty constructor to your model or annotate constructor parameters with @JsonProperty("field_name")
If you use a Kotlin data class then also can annotate with @JsonProperty("field_name") or register jackson module kotlin to ObjectMapper.
You can create your models using http://www.jsonschema2pojo.org/.
If you're using Lombok on a POJO model, make sure you have these annotations:
@Getter
@Builder
@NoArgsConstructor
@AllArgsConstructor
It could vary, but make sure @Getter and especially @NoArgsConstructor.
java - cannot deserialize from Object value (no delegate- or property-based Creator) even with default constructor present - Stack Overflow
ObjectMapper: getting a cannot deserialize from Object value error
Jackson3 Deserialization with Properties Based constructor fails with tools.jackson.databind.exc.InvalidDefinitionException
No Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator
EDIT:
I just found a much better solution, add the ParanamerModule to the ObjectMapper:
mapper.registerModule(new ParanamerModule());
Maven:
<dependency>
<groupId>com.fasterxml.jackson.module</groupId>
<artifactId>jackson-module-paranamer</artifactId>
<version>${jackson.version}</version>
</dependency>
The advantage against the ParameterNamesModule seems to be that the classes do not need to be compiled with the -parameters argument.
END EDIT
With Jackson 2.9.9 I tried to deserialize this simple POJO and came accros the same exception, adding a default constructor solved the problem:
POJO:
public class Operator {
private String operator;
public Operator(String operator) {
this.operator = operator;
}
public String getOperator() {
return operator;
}
}
ObjectMapper and Serialize/Deserialize:
ObjectMapper mapper = new ObjectMapper();
mapper.setVisibility(PropertyAccessor.ALL, Visibility.NONE);
mapper.setVisibility(PropertyAccessor.FIELD, Visibility.ANY);
mapper.setVisibility(PropertyAccessor.CREATOR, Visibility.ANY);
String value = mapper.writeValueAsString(new Operator("test"));
Operator result = mapper.readValue(value, Operator.class);
JSON:
{"operator":"test"}
Exception:
com.fasterxml.jackson.databind.exc.MismatchedInputException:
Cannot construct instance of `...Operator` (although at least one Creator exists): cannot deserialize from Object value (no delegate- or property-based Creator)
at [Source: (String)"{"operator":"test"}"; line: 1, column: 2]
Solution (POJO with default constructor):
public class Operator {
private String operator;
private Operator() {
}
public Operator(String operator) {
this();
this.operator = operator;
}
public String getOperator() {
return operator;
}
}
I observed this same issue. My issue was caused by me using the wrong JsonCreator type. I incorrectly used org.codehaus.jackson.annotate.JsonCreator, but should have used com.fasterxml.jackson.annotation.JsonCreator instead.
So I have code with an object mapper to convert a String of JSON to an object:
And the JSON in question looks like so:
{
"address": "url",
"position": {
"positionType" : "type"
},
"id": "id",
"obj": "*"
}So the object I have for the outer set of parameters is:
public class Example {
private String address;
private Position position;
private String id;
private String id;
private String obj;
//getters and setters for each field
}(Note that I tried to do without the Position object and was able to convert the rest of the fields no problem on their own)
But with the Position object to cover the innermost fields from the JSON:
public class Position {
private String positionType;
public String getPositionType() {
return positionType;
}
public void setPositionType(String positionType) {
this.positionType = positionType;
}When I include this and try to convert the whole JSON from earlier, I keep getting an error:
com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `Position` (although at least one Creator exists): cannot deserialize from Object value (no delegate- or property-based Creator)
Any ideas what I might be missing from Position? I can't understand since it worked with the outermost object on its own why the inclusion of the second object isn't working.
Adding the @Jacksonized Lombok annotation to your class got it working for me:
@Getter
@Builder(builderClassName = "Builder")
@JsonIgnoreProperties(ignoreUnknown = true)
@Jacksonized
public class Test {
Per the Lombok documentation:
The
@Jacksonizedannotation is an add-on annotation for@Builderand@SuperBuilder. It automatically configures the generated builder class to be used by Jackson's deserialization. It only has an effect if present at a context where there is also a@Builderor a@SuperBuilder; a warning is emitted otherwise.Without
@Jacksonized, you would have to customize your builder class(es). With@Jacksonized, you can simply write something like this to let Jackson use the generated builder:@Jacksonized @Builder @JsonIgnoreProperties(ignoreUnknown = true) public class JacksonExample { private List<Foo> foos; }
Use @ConstructorProperties from Java 8 beans module:
import java.beans.ConstructorProperties;
@ConstructorProperties({"prop1","prop2"})
public CustomClass(String prop1, String prop2) {
this.prop1 = prop1;
this.prop2 = prop2;
}