Complex XML using Spring Batch; StaxEventItemWriter ; Jaxb2Marshaller

Question

I need to write a slightly complex XML using Spring Batch. Can anyone please help me with the appropriate Spring configuration?

Below is the Output the process requires.

<XML>
<USERLIST ID="something" NAME="Sample">
  <USER ID="userID" NAME="Name"/>
  <USER ID="userID" NAME="Name"/>
  ........
</USERLIST>
<XML>

The 'UserList' in the XML above only needs to occur once

This is the spring configuration I have so far.

<bean id="userXMLWriter" class="org.springframework.batch.item.xml.StaxEventItemWriter">
    <property name="resource" value="file:outputs/users.xml" />
    <property name="encoding" value="ISO-8859-1" />
    <property name="version" value="1.0" />
    <property name="marshaller" ref="userXMLMarshaller" />
    <property name="rootTagName" value="XML" />
  </bean>

  <bean id="userXMLMarshaller" class="org.springframework.oxm.jaxb.Jaxb2Marshaller">
  <property name="marshallerProperties">
        <map>
            <entry>
                <key>
                    <util:constant static-field="javax.xml.bind.Marshaller.JAXB_FORMATTED_OUTPUT" />
               </key>
              <value type="java.lang.Boolean">true</value>
            </entry>
        </map>
    </property>
    <property name="classesToBeBound">
    <list>
        <value>org.test.model.xml.UserList</value>
        <value>org.test.model.xml.User</value>
    </list>
    </property>
  </bean>   

Obviously, when I test this my XML does not have the 'USERLIST' element in it because all these USER objects need to be added to the USERLIST somewhere. I am kinda new to Spring Batch and JAXB2. Any ideas on this is appreciated.

Thanks, Harish

Answer 1

The solution to this problem is to implement Header/Footer Callback classes provided by Spring (As Michael Minella suggested in the comments below.), StaxWriterCallback class in my case. Below is How I've implemented it.

<bean id="userXMLWriter" class="org.springframework.batch.item.xml.StaxEventItemWriter">
    <property name="resource" value="file:outputs/users.xml" />
    <property name="encoding" value="ISO-8859-1" />
    <property name="version" value="1.0" />
    <property name="marshaller" ref="userXMLMarshaller" />
    <property name="headerCallback" ref="UserXMLHeaderCallBack" />
    <property name="footerCallback" ref="UserXMLFooterCallBack"/>
    <property name="rootTagName" value="XML" />
 </bean>

<bean id="UserXMLHeaderCallBack" class ="org.test.writers.UserXMLHeaderCallBack"/>
<bean id="UserXMLFooterCallBack" class ="org.test.writers.UserXMLFooterCallBack"/>

  <bean id="userXMLMarshaller" class="org.springframework.oxm.jaxb.Jaxb2Marshaller">
     <property name="classesToBeBound">
     <list>
       <value>org.test.model.xml.User</value>
    </list>
    </property>
  </bean>  

And below are the Footer/Header callback classes implementation

 public class UserXMLHeaderCallBack implements StaxWriterCallback{  
      @Override
        public void write(XMLEventWriter writer) throws IOException {
            try{
            XMLEventFactory eventFactory = XMLEventFactory.newInstance();

            Attribute id = eventFactory.createAttribute("ID", "someId");
            Attribute name = eventFactory.createAttribute("NAME", "someName");
            List<Attribute> attributeList = Arrays.asList(id, name);
            List<?> nsList = Arrays.asList();

            XMLEvent event = eventFactory.createStartElement("", "", "USERLIST",attributeList.iterator(), nsList.iterator());
            writer.add(event);

            }catch(XMLStreamException e){
                System.err.println("Something went nuts!!!");
            }
        }

    }

Footer class

 public class UserXMLFooterCallBack implements StaxWriterCallback{

    @Override
    public void write(XMLEventWriter writer) throws IOException {
        try{
            XMLEventFactory eventFactory = XMLEventFactory.newInstance();

            XMLEvent event = eventFactory.createEndElement("", "", "USERLIST");
            writer.add(event);
        }catch(XMLStreamException e){
            System.err.println("Something went nuts!!!");
        }
    }

}

And I got the desired Output!