java - Jackson ObjectMapper DeserializationConfig.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT

Question

I am using Jackson for JSON serialization/deserialization in my Jersey application. I want to read the empty strings in JSON to null value in my java POJO property. I tried to set the DeserializationConfig.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT on Object Mapper but it is not working. Here is the code below

import java.io.IOException;
import org.codehaus.jackson.JsonParseException;
import org.codehaus.jackson.map.DeserializationConfig;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;

public class TestMapper {

    /**
     * @param args
     */
    public static void main(String[] args) {
        TestMapper.testJson();

    }

    public static void testJson(){
        String jsonString = "{"name":"First Name","phone":"","unknown":"test"}";
        ObjectMapper result = new ObjectMapper();
        //result.setDeserializationConfig(result.getDeserializationConfig().with(DeserializationConfig.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT));
        //result.enable(DeserializationConfig.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);
        /*DeserializationConfig deserializeConfig = result.getDeserializationConfig();
        deserializeConfig.with(DeserializationConfig.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);*/
        result.configure(DeserializationConfig.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT, true);
        result.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);

    try {
            TestBean testBean = result.readValue(jsonString, TestBean.class);
            if(testBean.getPhone()!=null&& testBean.getPhone().equals("")){
                System.out.print("Phone Number is empty string");
            }else{
                System.out.print("Phone Number is null");
            }
        } catch (JsonParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (JsonMappingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}

The bean is as below

public class TestBean {

    private String name;
    private String phone;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getPhone() {
        return phone;
    }
    public void setPhone(String phone) {
        this.phone = phone;
    }
    public TestBean(String name, String phone) {
        super();
        this.name = name;
        this.phone = phone;
    }
    public TestBean() {
        super();
    }


}

The output is always

Phone Number is empty string

I am not sure why is this not working. I am using Jackson 1.9.2.

Answer 1

Note the javadoc of ACCEPT_EMPTY_STRING_AS_NULL_OBJECT

Feature that can be enabled to allow JSON empty String value ("") to be bound to POJOs as null.

So an empty String can be used to map null to a POJO. A String is not a POJO, it is considered a JSON primitive value.

You cannot use that here.

ACCEPT_EMPTY_STRING_AS_NULL_OBJECT would work for something like

{"name":"First Name","phone":"","unknown":"test"}

Where you would make the TestBean.phone field of some POJO type like

class Phone {
    private String number;
}

Then deserializing would make the phone field be null.