Is there a way when using @ResponseBody annotation to have null values mapped to empty strings?
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2 Answers
You will have to write a custom Jackson Serializer - a good example is here - http://wiki.fasterxml.com/JacksonHowToCustomSerializers (there is a specific example of how to convert null values to empty Strings that you can use)
Here are all the steps(for Jackson < 2.0):
Write your custom null Serializer:
import java.io.IOException;
import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.JsonProcessingException;
import org.codehaus.jackson.map.JsonSerializer;
import org.codehaus.jackson.map.SerializerProvider;
public class NullSerializer extends JsonSerializer<Object> {
@Override
public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
jgen.writeString("");
}
}
Register this with Jackson Objectmapper:
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.map.ser.StdSerializerProvider;
public class CustomObjectMapper extends ObjectMapper{
public CustomObjectMapper(){
StdSerializerProvider sp = new StdSerializerProvider();
sp.setNullValueSerializer(new NullSerializer());
this.setSerializerProvider(sp);
}
}
Register this objectmapper with Spring MVC:
<mvc:annotation-driven>
<mvc:message-converters register-defaults="true">
<bean class="org.springframework.http.converter.json.MappingJacksonHttpMessageConverter">
<property name="objectMapper">
<bean class="CustomObjectMapper"/>
</property>
</bean>
</mvc:message-converters>
</mvc:annotation-driven>
3 Comments
pethel
Ok but I have to set up this in the application context? So far I did nothing except including Jackson jars in classpath.
Trant
I get this error in the spring config xml: Element 'mvc:annotation-driven' must have no character or element information item [children], because the type's content type is empty.
Trant
Got that error sorted out - was using older version of spring xml shcema - however solution does not work. breakpoint on NullSerializer never hit, though one on CustomerObjectMapper is hit. Dates still coming out as: "someDate":null instead of the desired "someDate":""
I have also faced the same problem in my project and I have therefore quickly come up with a solution for the same. This post will surely help all those who have been struggling with the same issue.
Step 1:- Create your Custom Null Handler Serializer.
public class NullSerializer extends StdSerializer<Object> {
public NullSerializer(Class<Object> t) {
super(t);
}
public NullSerializer() {
this(null);
}
@Override
public void serialize(Object o, com.fasterxml.jackson.core.JsonGenerator jsonGenerator, com.fasterxml.jackson.databind.SerializerProvider serializerProvider) throws IOException {
jsonGenerator.writeString("");
}
}
Step 2:- Create a bean of MappingJackson2HttpMessageConverter.
@Bean
@Primary
public MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter() {
MappingJackson2HttpMessageConverter jsonConverter = new MappingJackson2HttpMessageConverter();
ObjectMapper mapper = new ObjectMapper();
mapper.setPropertyNamingStrategy(PropertyNamingStrategy.SNAKE_CASE);
mapper.getSerializerProvider().setNullValueSerializer(new NullSerializer());
jsonConverter.setObjectMapper(mapper);
return jsonConverter;
}
Thank you for taking some time out to read this post. I hope that this was able to resolve your queries to some extent.
