I have an object like this to deserialize:
public class RelationsInput {
Relation relation1;
Relation relation2;
}
whereas the class Relation looks like this:
public class Relation {
RelationType relationtype;
... (more fields)
}
RelationType is en enum and is not a value which will be deserialized, while all others are.
Is it possible, that I could “inject” the enum value for the field relationType with an annotation on the field in the class RelationInput?
Like the following
public class RelationsInput {
@RelationType(RelationType.OWNER)
Relation owner;
@RelationType(RelationType.TENANT)
Relation tenant;
}
Does Jackson provide something like this?
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Answer
You can try to implement custom deserialiser with com.fasterxml.jackson.databind.deser.ContextualDeserializer interface. It allows to create deserialiser instance with a context.
See below example:
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.BeanProperty;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.deser.ContextualDeserializer;
import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
import com.fasterxml.jackson.databind.json.JsonMapper;
import lombok.Data;
import java.io.File;
import java.io.IOException;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
public class JsonContextualDeserializerApp {
public static void main(String[] args) throws IOException {
File jsonFile = new File("./resource/test.json").getAbsoluteFile();
ObjectMapper mapper = JsonMapper.builder().build();
RelationsInput info = mapper.readValue(jsonFile, RelationsInput.class);
System.out.println(info.toString());
}
}
@Data
class RelationsInput {
@JsonDeserialize(using = RelationStdDeserializer.class)
@RelationTypeInfo(RelationType.OWNER)
private Relation owner;
@JsonDeserialize(using = RelationStdDeserializer.class)
@RelationTypeInfo(RelationType.TENANT)
private Relation tenant;
}
@Data
class Relation {
private int id;
private RelationType relationtype;
}
enum RelationType {OWNER, TENANT}
@Retention(RetentionPolicy.RUNTIME)
@interface RelationTypeInfo {
RelationType value();
}
class RelationStdDeserializer extends StdDeserializer<Relation> implements ContextualDeserializer {
private RelationType propertyRelationType;
public RelationStdDeserializer() {
this(null);
}
public RelationStdDeserializer(RelationType relationType) {
super(Relation.class);
this.propertyRelationType = relationType;
}
@Override
public Relation deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
JsonDeserializer<Object> deser = ctxt.findRootValueDeserializer(ctxt.getTypeFactory().constructType(Relation.class));
Relation instance = (Relation) deser.deserialize(p, ctxt);
if (this.propertyRelationType != null) {
instance.setRelationtype(this.propertyRelationType);
}
return instance;
}
@Override
public JsonDeserializer<?> createContextual(DeserializationContext ctxt, BeanProperty property) {
RelationTypeInfo typeInfo = property.getMember().getAllAnnotations().get(RelationTypeInfo.class);
return new RelationStdDeserializer(typeInfo.value());
}
}
Above code for a payload:
{
"owner": {
"id": 1
},
"tenant": {
"id": 2
}
}
prints:
RelationsInput(owner=Relation(id=1, relationtype=OWNER), tenant=Relation(id=2, relationtype=TENANT))
See also: