使用Jackson对序列化的最终类进行反序列化

Question

I have following value holder class for users:

package entities;

import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import org.immutables.value.Value;

import javax.annotation.Nullable;

@Value.Immutable
@JsonSerialize(as = ImmutableUser.class)
@JsonDeserialize(as = ImmutableUser.class)
@JsonTypeInfo(use = JsonTypeInfo.Id.CLASS)
public interface User {

    String getUsername();
    String getEmail();
    @Nullable String getPassword();
    @Nullable String getEncodedPassword();
}

Immutable final implementation of this value holder is being generated during compilation:

@SuppressWarnings("all")
@ParametersAreNonnullByDefault
@Generated({"Immutables.generator", "User"})
@Immutable
public final class ImmutableUser implements User {

Serialized instance of Immutable

{"@class":"entities.ImmutableUser$Json","username":"testuser","email":"123@gmail.com","password":null,"encodedPassword":null}

The problem is that deserialization of this JSON fails with following error:

java.lang.IllegalArgumentException: Class entities.ImmutableUser$Json is not assignable to entities.User
    at com.fasterxml.jackson.databind.JavaType._assertSubclass(JavaType.java:466)
    at com.fasterxml.jackson.databind.JavaType.narrowBy(JavaType.java:149)
    at com.fasterxml.jackson.databind.type.TypeFactory.constructSpecializedType(TypeFactory.java:315)
    at com.fasterxml.jackson.databind.jsontype.impl.ClassNameIdResolver._typeFromId(ClassNameIdResolver.java:64)
    ... 38 more

Why does @class property in JSON for serialized instance have value "entities.ImmutableUser$Json" instead of "entities.ImmutableUser" ? Is it because of fact that the class is final ? Is there any other way to serialize such classes and to avoid problems during deserialization?

Answer 1

Found out that the problem was caused by generated class. Turns out that such classes should be marshaled using specific classes: immutables.github.io/site1.x/json.html

Answer 2

The http://immutables.github.io/site1.x/json.html is referring to the older version of documentation and is quite irrelevant if you use Immutables v2.0 and up. In your case you're facing an already fixed issue (similar to https://github.com/immutables/immutables/issues/175 ). Try upgrading to Immutables v2.1 to get it resolved.

In nutshell, Jackson have feature annotation @JsonValue to substitute object during serialization. Unfortunately as we found out that it does not play well with other functionality as @JsonTypeInfo and @JsonSubTypes . See https://github.com/FasterXML/jackson-databind/issues/937 .

Version 2.1 of Immutables no longer used @JsonValue , so it should work now. If not, please report it as a bug to https://github.com/immutables/immutables/issues