Can Jackson be configured to trim leading/trailing whitespace from all string properties?
Example JSON (note that the string has trailing spaces):
{ "aNumber": 0, "aString": "string " }
Ideally, the deserialised instance would have an aString property with a value of "string" (i.e. without trailing spaces). This seems like something that is probably supported but I can't find it (e.g. in DeserializationConfig.Feature).
We're using Spring MVC 3.x so a Spring-based solution would also be fine.
I tried configuring Spring's WebDataBinder based on a suggestion in a forum post but it does not seem to work when using a Jackson message converter:
@InitBinder
public void initBinder( WebDataBinder binder )
{
binder.registerCustomEditor( String.class, new StringTrimmerEditor( " \t\r\n\f", true ) );
}
Easy solution for Spring Boot users, just add that walv's SimpleModule extension to your application context:
package com.example;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.deser.std.StdScalarDeserializer;
import com.fasterxml.jackson.databind.module.SimpleModule;
import org.springframework.stereotype.Component;
import java.io.IOException;
@Component
public class StringTrimModule extends SimpleModule {
public StringTrimModule() {
addDeserializer(String.class, new StdScalarDeserializer<String>(String.class) {
@Override
public String deserialize(JsonParser jsonParser, DeserializationContext ctx) throws IOException,
JsonProcessingException {
return jsonParser.getValueAsString().trim();
}
});
}
}
Another way to customize Jackson is to add beans of type com.fasterxml.jackson.databind.Module to your context. They will be registered with every bean of type ObjectMapper, providing a global mechanism for contributing custom modules when you add new features to your application.
http://docs.spring.io/spring-boot/docs/current/reference/html/howto-spring-mvc.html#howto-customize-the-jackson-objectmapper
if you are not using spring boot, you have to register the StringTrimModule yourself (you do not need to annotate it with @Component)
<bean class="org.springframework.http.converter.json.Jackson2ObjectMapperFactoryBean">
<property name="modulesToInstall" value="com.example.StringTrimModule"/>
</bean
With a custom deserializer, you could do the following:
<your bean>
@JsonDeserialize(using=WhiteSpaceRemovalSerializer.class)
public void setAString(String aString) {
// body
}
<somewhere>
public class WhiteSpaceRemovalDeserializer extends JsonDeserializer<String> {
@Override
public String deserialize(JsonParser jp, DeserializationContext ctxt) {
// This is where you can deserialize your value the way you want.
// Don't know if the following expression is correct, this is just an idea.
return jp.getCurrentToken().asText().trim();
}
}
This solution does imply that this bean attribute will always be serialized this way, and you will have to annotate every attribute that you want to be deserialized this way.