Jackson ignores ACCEPT_EMPTY_STRING_AS_NULL_OBJECT [duplicate] - angularjs

Question

This question already has an answer here:
Jackson ObjectMapper DeserializationConfig.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT
(1 answer)
Closed 6 years ago.
I need to treat the empty string ("") as null in Spring MVC. This because I found that when I edit a form field (with Angular's ng-model) that was originally undefined, then erase it to blank, Angular will send that bean property as empty string. If I don't touch such null value, it won't be sent in the JSON payload and thus treated as null.
I have configured Jackson with the ACCEPT_EMPTY_STRING_AS_NULL_OBJECT DeserializationFeature in my Spring context. Configuration below:
<bean id="jacksonMessageConverter" class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
<constructor-arg>
<bean class="org.springframework.http.converter.json.Jackson2ObjectMapperFactoryBean">
<property name="featuresToDisable">
<array>
<util:constant static-field="com.fasterxml.jackson.databind.SerializationFeature.WRITE_DATES_AS_TIMESTAMPS" />
</array>
</property>
<property name="featuresToEnable">
<array>
<util:constant static-field="com.fasterxml.jackson.databind.SerializationFeature.INDENT_OUTPUT" />
<util:constant static-field="com.fasterxml.jackson.databind.SerializationFeature.WRITE_ENUMS_USING_TO_STRING" />
<util:constant static-field="com.fasterxml.jackson.databind.DeserializationFeature.READ_ENUMS_USING_TO_STRING" />
<util:constant static-field="com.fasterxml.jackson.databind.DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT" />
</array>
</property>
<property name="serializationInclusion">
<util:constant static-field="com.fasterxml.jackson.annotation.JsonInclude.Include.NON_NULL" />
</property>
</bean>
</constructor-arg>
<property name="supportedMediaTypes">
<array>
<value>application/json</value>
</array>
</property>
</bean>
Still, it looks like it decodes empty strings as empty strings rather than null. I have debugged and I could see "" in the payload. Here is a sample from an admin page
{
"id":"ADMIN.NOTIFIER_SMTP",
"host":"aa.bb.cc",
"protocol":"POP",
"securityProtocol":"PLAIN",
"username":"", <----- shall be null on server, I don't care about client
"passwordSet":false
}
Question is: is something wrong in my configuration? How do I tell Jackson to treat empty as null?

Answer 1

May be you want to write a CustomObjectMapper
<mvc:annotation-driven>
<mvc:message-converters>
<bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
<property name="objectMapper">
<bean class="custom.CustomObjectMapper"/>
</property>
</bean>
</mvc:message-converters>
</mvc:annotation-driven>
and add above deserializer in it.

Answer 2

Jackson will give you null for other objects, but for String it will give empty String.
But you can use a Custom JsonDeserializer to do this:
class CustomDeserializer extends JsonDeserializer<String> {
#Override
public String deserialize(JsonParser jsonParser, DeserializationContext context) throws IOException, JsonProcessingException {
String node = jsonParser.readValueAs(String.class);
if (StringUtils.isBlank(node)) {
return null;
}
return node;
}}
In class you have to use it for location field:
class EventBean {
public Long eventId;
public String title;
#JsonDeserialize(using = CustomDeserializer.class)
public String location;
}