How to instantiate an empty element with JAXB

Question

I use JAXB to create XML messages. The XML I need to create is (for the sake of simplicity):

<request>
  <header/>
</request>

My code looks like this:

import javax.xml.bind.annotation.*;

@XmlRootElement(name = "request")
public class Request {

    private String header;

    @XmlElement(required=true)
    public String getHeader() {
      return header;
    }

    public void setHeader(String header) {
      this.header=header;
    }
}

The problem: the header element is not displayed (header is null). When header is set to an empty string, the following is displayed:

<request>
  <header></header>
</request>

When I use as type Object instead of String, the result is even worse:

<request>
  <header xsi:type="xs:string" 
   xmlns:xs="http://www.w3.org/2001/XMLSchema" 
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"&gt;&lt;/header&gt;
</request>

BTW: I'm using this code to create the XML string.

Is it possible to get an empty tag?

Answer 1

In XML, <header/> and <header></header> are the same thing. If you really want the former, then use a prettifier. javax.xml.transform.TransformerFactory.newTransformer() will probably do that for you.

Answer 2

An empty tag for a String object is essentially the empty string.

If you call the following, you will get what you are looking for:

request.setHeader("")

I should also note that in XML the following two declarations of a header are idential. Both of these have no child text nodes. These are essentially the same and will be treated the same by all XML parsers:

<header></header>

<header/>

Answer 3

How about the other type properties? Like List,if it was setted to null ,then in the xml it can't be found too. How can I create a empty tag for null List?