使用 JAXB 解组日期但出现空指针异常

Question

I am trying to convert XML to java object. In my xml, there is field which looks like:

<pickDisplayTs>2021-09-24T18:03:06.603 +0000</pickDisplayTs>

My Java object looks like the following:

@XmlElement(name = "pickDisplayTs" )
@XmlJavaTypeAdapter(DateAdapter.class)
public Date pickDisplayTs;

My DataAdapter class is the following:

    import javax.xml.bind.annotation.adapters.XmlAdapter;
    import java.text.SimpleDateFormat;
    import java.util.Date;

   public class DateAdapter extends XmlAdapter<String, Date> {

   private static final String CUSTOM_FORMAT_STRING = "yyyy-MM- 
   dd'T'HH:mm:ss.SSS'Z'";


    @Override
    public Date unmarshal(String v) throws Exception {
    return new SimpleDateFormat(CUSTOM_FORMAT_STRING).parse(v);
   }

@Override
public String marshal(Date v) throws Exception {
    return new SimpleDateFormat(CUSTOM_FORMAT_STRING).format(v);
}

}

Code reference: https://github.com/eugenp/tutorials/blob/950bbadc353bdca114befc98cf4a18476352220e/jaxb/src/main/java/com/baeldung/jaxb/dateunmarshalling/DateAdapter.java

This is the method for unmarshalling the xml file:

  String filepath = "xml/PickComplete.xml";
  String xmlPickComplete = readFromResources(filepath);
  PickComp pickCompleteMq = Xml.xmlToObject(xmlPickComplete, PickingSubSystemOrderCompleteMessage.class);

The entire pickCompleteMq is coming to be null but if I am declaring the pickDisplayTs as string, its all good, not sure where I am going wrong. But I need the field to be in Date.

Any help will be appreciated. Thank you.

Answer 1

The problem is with the input. XML extract you have provided doesn't follow the DateAdapter you are using. If you marshal a pojo that contain Date the expected xml tag should be

<pickDisplayTs>2022-02-16T14:02:13.010Z</pickDisplayTs>

Trying to parse the given input gives ParseException. Code snippet:

Date parse = new SimpleDateFormat(CUSTOM_FORMAT_STRING).parse("2021-09-24T18:03:06.603 +0000");
System.out.println(parse);

Output

java.text.ParseException: Unparseable date: "2021-09-24T18:03:06.603 +0000"
at java.text.DateFormat.parse(DateFormat.java:366)

Solution proposal:

    private static final String CUSTOM_FORMAT_STRING = "yyyy-MM-dd'T'HH:mm:ss.SSS Z";
    public static void main(String[] args) throws ParseException {
        String dateStr = "2021-09-24T18:03:06.603 +0000";
        Date marshaledDate = new SimpleDateFormat(CUSTOM_FORMAT_STRING).parse(dateStr);

        SimpleDateFormat format = new SimpleDateFormat(CUSTOM_FORMAT_STRING);
        format.setTimeZone(TimeZone.getTimeZone("UTC"));

        String unmarshalledDate = format.format(marshaledDate);
        System.out.println(unmarshalledDate);
    }

You can use the above logic in your DataAdapter class as follows:

public class DateAdapter extends XmlAdapter<String, Date> {
        private static final String CUSTOM_FORMAT_STRING = "yyyy-MM-dd'T'HH:mm:ss.SSS Z";

        @Override
        public Date unmarshal(String v) throws Exception {
            return new SimpleDateFormat(CUSTOM_FORMAT_STRING).parse(v);
        }

        @Override
        public String marshal(Date v) throws Exception {
            SimpleDateFormat sdf = new SimpleDateFormat(CUSTOM_FORMAT_STRING);
            sdf.setTimeZone(TimeZone.getTimeZone("UTC"));
            return sdf.format(v);
        }
    }