Jackson Deserialization not calling deserialize on Custom Deserializer

Michael Coxon :

I want to deserialize classes of the form:

public class TestFieldEncryptedMessage implements ITextMessage {

    @JsonProperty("text")
    @Encrypted(cipherAlias = "testAlias")
    private String text;

    public TestFieldEncryptedMessage() {
    }

    @JsonCreator
    public TestFieldEncryptedMessage(@JsonProperty("text") String text) {
        this.text = text;
    }

    public String getText() {
        return text;
    }

    public void setText(String text) {
        this.text = text;
    }
}

Where the text is encrypted and deserialization should unencrypt the value before rebuilding the TestFieldEncryptedMessage instance.

I am following an approach very similar to: https://github.com/codesqueak/jackson-json-crypto

That is, I am building a module extending SimpleModule:

public class CryptoModule extends SimpleModule {
    public final static String GROUP_ID = "au.com.auspost.messaging";
    public final static String ARTIFACT_ID = "jackson-json-crypto";
    private EncryptedSerializerModifier serializerModifier;
    private EncryptedDeserializerModifier deserializerModifier;

    public CryptoModule() {
    }

   public CryptoModule addEncryptionService(final EncryptionService encryptionService) {
        serializerModifier = new EncryptedSerializerModifier(encryptionService);
        deserializerModifier = new EncryptedDeserializerModifier(encryptionService);
        return this;
    }

    @Override
    public String getModuleName() {
        return ARTIFACT_ID;
    }

    @Override
    public Version version() {
        return new Version(major, minor, patch, null, GROUP_ID, ARTIFACT_ID);
    }

    @Override
    public void setupModule(final SetupContext context) {
        if ((null == serializerModifier) || (null == deserializerModifier))
            throw new EncryptionException("Crypto module not initialised with an encryption service");
        context.addBeanSerializerModifier(serializerModifier);
        context.addBeanDeserializerModifier(deserializerModifier);
    }
}

As you can see, two modifiers are set up: the EncryptedSerializerModifier works perfectly and is called by the ObjectMapper, but the deserializer behind the EncryptedDeserializerModifier is ignored.

As is seen in many other examples on SO such as here: How can I include raw JSON in an object using Jackson?, I set up the EncryptedDeserializerModifier with:

public class EncryptedDeserializerModifier extends BeanDeserializerModifier {

    private final EncryptionService encryptionService;

    private Map<String, SettableBeanProperty> properties = new HashMap<>();

    public EncryptedDeserializerModifier(final EncryptionService encryptionService) {
        this.encryptionService = encryptionService;
    }

    @Override
    public BeanDeserializerBuilder updateBuilder(final DeserializationConfig config, final BeanDescription beanDescription, final BeanDeserializerBuilder builder) {

        Encrypted annotation = beanDescription.getType().getRawClass().getAnnotation(Encrypted.class);
        Iterator it = builder.getProperties();

        while (it.hasNext()) {
            SettableBeanProperty p = (SettableBeanProperty) it.next();

            if (null != p.getAnnotation(Encrypted.class)) {
                JsonDeserializer<Object> current = p.getValueDeserializer();
                properties.put(p.getName(), p);

                builder.addOrReplaceProperty(p.withValueDeserializer(new EncryptedJsonDeserializer(encryptionService, current, p)), true);
            }
        }
        return builder;
    }
}

Finally, the EncryptedJsonDeserializer itself overrides the following:

@Override
public Object deserialize(final JsonParser parser, final DeserializationContext context) throws JsonMappingException {
    JsonDeserializer<?> deserializer = baseDeserializer;

    if (deserializer instanceof ContextualDeserializer) {
        deserializer = ((ContextualDeserializer) deserializer).createContextual(context, property);
    }

    return service.decrypt(parser, deserializer, context, property != null ? property.getType() : type);
}

@Override
public JsonDeserializer<?> createContextual(final DeserializationContext context, final BeanProperty property) throws JsonMappingException {
    JsonDeserializer<?> wrapped = context.findRootValueDeserializer(property.getType());
    return new EncryptedJsonDeserializer(service, wrapped, property);
}

The createContextual() method is called, but the deserialize method is not called. The property throughout the execution is always the "text" property, so I seem to have the right context.

anyone know why the ObjectMapper doesn't find the right Deserializer?

EDIT added implements ITextMessage to decrypted class, which I thought was an unimportant detail, but turned out to be the cause of the issue.

Michael Coxon :

I found the issue! If you look closely at the TestFieldEncryptedMessage class, whose text field is encrypted, you can see that it implements an interface. The interface is used so that the messages give some extra tooling for asserts in tests, however for deserialization, there is an unintended consequence. When the ObjectMapper is working its way through the json string, it tries, I think, to match a deserializer to a field inside ITextMessage, not to a field inside TestFieldEncryptedMessage, which is why the custom deserializer was not called (there is no text field in ITextMessage).

Once I stopped implementing ITextMessage, the custom deserializer was called.