Jackson ObjectMapper DeserializationConfig.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT
jackson, java, json, json-deserialization
Solution
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`.
Problem
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.