Hello,
I have a problem with a deserializer I am working on.
At the deserializer I want to register values, which indicate that the
resulting Optional<T> should be empty. But if the value in the JSON string
is null, the Optional<T> will be null as well, else it works as expected.
Here is the code for the deserializer:
public class EmptyOptionalDeserializer extends JsonDeserializer<Optional<?>>
implements ContextualDeserializer {
private Map<Class<?>, Set<Object>> emptyValues;
private JavaType valueType;
public EmptyOptionalDeserializer() {
this(Collections.synchronizedMap(new HashMap<>()), null);
}
/**
* This constructor is only used for the contextual deserialization.
* @param emptyValues Reference to the empty values map.
* @param valueType Optional's value type.
*/
protected EmptyOptionalDeserializer(Map<Class<?>, Set<Object>>
emptyValues, JavaType valueType) {
this.emptyValues = emptyValues;
this.valueType = valueType;
}
/**
* {@inheritDoc}
*/
@Override
public JsonDeserializer<?> createContextual(DeserializationContext ctxt,
BeanProperty property) throws JsonMappingException {
return new EmptyOptionalDeserializer(emptyValues, property.getType
().containedType(0));
}
/**
* {@inheritDoc}
*/
@Override
public Optional<?> deserialize(JsonParser parser, DeserializationContext
ctxt) throws IOException, JsonProcessingException {
Object value = ctxt.readValue(parser, valueType);
if(value == null) {
return Optional.empty();
}
if(!emptyValues.containsKey(valueType.getRawClass())) { // class
not registered
return Optional.of(value);
}
Set<Object> emptyValues = this.emptyValues.get(valueType.getRawClass
());
if(emptyValues == null) {
return Optional.of(value);
}
return emptyValues.contains(value) ? Optional.empty() : Optional.of(
value);
}
/**
* Registers values for a type which will count as empty optional.
* @param type Type to register empty values for.
* @param emptyValues Empty values.
* @return Returns itself for method chaining.
*/
public EmptyOptionalDeserializer register(Class<?> type, Object...
emptyValues) {
Collections.addAll(this.emptyValues.computeIfAbsent(type, t -> new
HashSet<>()), emptyValues);
return this;
}
}
If I have a JSON string like
{"test":null}
and a POJO like
public class A {
public Optional<String> test;
}
and create the ObjectMapper like
new ObjectMapper()
.registerModule(
new SimpleModule()
.addDeserializer(
Optional.class,
new EmptyOptionalDeserializer()
.register(String.class, "")
)
);
and try to deserialize it to A, the Optional A.test will be null. The
EmptyOptionalDeserializer#createContextual method will be called and thus
the actual deserializer will created, but its deserialize method is not
called.
If it were
{"test":""}
the deserializer would work as expected.
What am I doing wrong?
Regards.
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