问Genson 1.4 (JSON)不处理继承的Pojo

EN

This is my BaseObject

public class SynBaseObject implements Serializable
{
 private Long status;
//GettersAndSetters
}

public class PhoneNumber extends SynBaseObject
{
private  String      countryCode;
private  String      areaCode;
private  String      localNumber;
//GettersAndSetters
}

public class ResponseObject  implements Serializable
{ 
private Integer errorCode;
private String errorMessage;
private Long    primaryKey;

private SynBaseObject baseClass;

public ResponseObject()
{

}

public SynBaseObject getBaseObject()
{
return baseClass;
}

public void setBaseObject(SynBaseObject baseClass)
{
this.baseClass = baseClass;
}

public Integer getErrorCode()
{
return errorCode;
}

public void setErrorCode(Integer errorCode)
{
this.errorCode = errorCode;
}

    Genson genson = new Genson();
    PhoneNumber number = new PhoneNumber();
    number.setCountryCode("2");
    number.setAreaCode("3");
    number.setLocalNumber("9645");
    ResponseObject responseObject = new ResponseObject();
    responseObject.setBaseObject(number);
    String serialize = genson.serialize(responseObject);
    System.out.println(serialize);