JAXB element name based on object property

Question

I have to create object model for following XMLs:

XML sample 1:

<InvoiceAdd>
  <TxnDate>2009-01-21</TxnDate>
  <RefNumber>1</RefNumber>
  <InvoiceLineAdd>
  </InvoiceLineAdd>
</InvoiceAdd>

XML Sample 2:

<SalesOrderAdd>
  <TxnDate>2009-01-21</TxnDate>
  <RefNumber>1</RefNumber>
  <SalesOrderLineAdd>
  </SalesOrderLineAdd>
</SalesOrderAdd>

The XML output will be based on a single string parameter or enum. String txnType = "Invoice"; (or "SalesOrder");

I would use single class TransactionAdd:

@XmlRootElement
public class TransactionAdd {  
  public String txnDate;
  public String refNumber;

  private String txnType;
  ...

  public List<LineAdd> lines;
}

instead of using subclasses or anything else. The code which creates the TransactionAdd instance is the same for both types of transaction it only differs on the type.

This XML is used by a rather known product called QuickBooks and is consumed by QuickBooks web service - so I can't change the XML, but I want to make it easy to be able to set element name based on property (txnType).

I would consider something like a method to determine target element name:

@XmlRootElement
public class TransactionAdd {  
  public String txnDate;
  public String refNumber;

  private String txnType;
  ...

  public List<LineAdd> lines;

  public String getElementName() {
     return txnType + "Add";
  }
}

Different transactions will be created using following code:

t = new TransactionAdd();
t.txnDate = "2010-12-15";
t.refNumber = "123";
t.txnType = "Invoice";

The goal is to serialize t object with the top-level element name based on txnType. E.g.:

<InvoiceAdd>
   <TxnDate>2009-01-21</TxnDate>
   <RefNumber>1</RefNumber>
</InvoiceAdd>

In case of t.txnType = "SalesOrder" the result should be

<SalesOrderAdd>
   <TxnDate>2009-01-21</TxnDate>
   <RefNumber>1</RefNumber>
</SalesOrderAdd>

At the moment I see only one workaround with subclasses InvoiceAdd and SalesOrderAdd and using @XmlElementRef annotation to have a name based on class name. But it will need to instantiate different classes based on transaction type and also will need to have two other different classes InvoiceLineAdd and SalesOrderLineAdd which looks rather ugly.

Please suggest me any solution to handle this. I would consider something simple.

Solution 1

To address the root element aspect you could do will need to leverage @XmlRegistry and @XmlElementDecl. This will give us multiple possible root elements for the TransactionAdd class:

import javax.xml.bind.JAXBElement;
import javax.xml.bind.annotation.XmlElementDecl;
import javax.xml.bind.annotation.XmlRegistry;
import javax.xml.namespace.QName;

@XmlRegistry
public class ObjectFactory {

    @XmlElementDecl(name="InvoiceAdd")
    JAXBElement<TransactionAdd> createInvoiceAdd(TransactionAdd invoiceAdd) {
        return new JAXBElement<TransactionAdd>(new QName("InvoiceAdd"), TransactionAdd.class, invoiceAdd);
    }

    @XmlElementDecl(name="SalesOrderAdd")
    JAXBElement<TransactionAdd> createSalesOrderAdd(TransactionAdd salesOrderAdd) {
        return new JAXBElement<TransactionAdd>(new QName("SalesOrderAdd"), TransactionAdd.class, salesOrderAdd);
    }

}

Your TransactionAdd class will look something like the following. The interesting thing to note is that we will make the txnType property @XmlTransient.

import java.util.List;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlTransient;

public class TransactionAdd {

    private String txnDate;
    private String refNumber;
    private String txnType;
    private List<LineAdd> lines;

    @XmlElement(name="TxnDate")
    public String getTxnDate() {
        return txnDate;
    }

    public void setTxnDate(String txnDate) {
        this.txnDate = txnDate;
    }

    @XmlElement(name="RefNumber")
    public String getRefNumber() {
        return refNumber;
    }

    public void setRefNumber(String refNumber) {
        this.refNumber = refNumber;
    }

    @XmlTransient
    public String getTxnType() {
        return txnType;
    }

    public void setTxnType(String txnType) {
        this.txnType = txnType;
    }

    public List<LineAdd> getLines() {
        return lines;
    }

    public void setLines(List<LineAdd> lines) {
        this.lines = lines;
    }

}

Then we need to supply a little logic outside the JAXB operation. For an unmarshal we will use the local part of the root element name to populate the txnType property. For a marshal we will use the value of the txnType property to create the appropriate JAXBElement.

import java.io.File;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBElement;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(TransactionAdd.class, ObjectFactory.class);

        File xml = new File("src/forum107/input1.xml");
        Unmarshaller unmarshaller = jc.createUnmarshaller();
        JAXBElement<TransactionAdd> je = (JAXBElement<TransactionAdd>) unmarshaller.unmarshal(xml);
        TransactionAdd ta = je.getValue();
        ta.setTxnType(je.getName().getLocalPart());

        JAXBElement<TransactionAdd> jeOut;
        if("InvoiceAdd".equals(ta.getTxnType())) {
            jeOut = new ObjectFactory().createInvoiceAdd(ta);
        } else {
            jeOut = new ObjectFactory().createSalesOrderAdd(ta);
        }
        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(jeOut, System.out);
    }

}

To Do

I will look into addressing the lines property next.

Solution 2

You could use an XmlAdapter for this. Based on the String value of the txnType property you would have the XmlAdapter marshal an instance of an Object corresponding to InvoiceLineAdd or SalesOrderLineAdd.

This is how it would look:

TransactionAdd

On the txnType property we will use a combination of @XmlJavaTypeAdapter and @XmlElementRef:

import javax.xml.bind.annotation.XmlElementRef;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;

@XmlRootElement
public class TransactionAdd {

    private String txnType;

    @XmlJavaTypeAdapter(MyAdapter.class)
    @XmlElementRef
    public String getTxnType() {
        return txnType;
    }

    public void setTxnType(String txnType) {
        this.txnType = txnType;
    }

}

The adapted objects will look like:

AbstractAdd

import javax.xml.bind.annotation.XmlSeeAlso;

@XmlSeeAlso({InvoiceAdd.class, SalesOrderAdd.class})
public class AbstractAdd {

}

InvoiceAdd

import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class InvoiceAdd extends AbstractAdd {

}

SalesOrderAdd

import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class SalesOrderAdd extends AbstractAdd {

}

The XmlAdapter to convert between the String and the adapted objects will look like:

import javax.xml.bind.annotation.adapters.XmlAdapter;

public class MyAdapter extends XmlAdapter<AbstractAdd, String> {

    @Override
    public String unmarshal(AbstractAdd v) throws Exception {
        if(v instanceof SalesOrderAdd) {
            return "salesOrderAdd";
        }
        return "invoiceAdd";
    }

    @Override
    public AbstractAdd marshal(String v) throws Exception {
        if("salesOrderAdd".equals(v)) {
            return new SalesOrderAdd();
        } 
        return new InvoiceAdd();
    }

}

The following demo code can be used:

import java.io.File;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(TransactionAdd.class);

        File xml = new File("input.xml");
        Unmarshaller unmarshaller = jc.createUnmarshaller();
        TransactionAdd ta = (TransactionAdd) unmarshaller.unmarshal(xml);

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(ta, System.out);
    }

}

To produce/consume the following XML:

<transactionAdd>
    <salesOrderAdd/>
</transactionAdd>

For more information see:

• http://bdoughan.blogspot.com/2010/07/xmladapter-jaxbs-secret-weapon.html

Comments

[Vladimir]

Great! Thanks @Blaise, I've read your blog but missed this post. Now I see that it can help me. Give one more little note. Could I use something like new JAXBElement(new QName("SalesOrderLineAdd"), LineAdd.class, lineAddObject) as output of marshal method in the adapter?

[bdoughan]

@Vladimir: I've updated my answer with a code example. The trick is to use @XmlJavaTypeAdapter and @XmlElementRef together.

[Vladimir]

@Blaise, let's assume I want to substitute object a with object b. But I want object b to be object a with another top-level element name, but the same content. Is it possible to use somekind of special wrapper to do that. Something like: new JAXBWrapper("b", a)?

[Vladimir]

@Blaise, I've updated the question with sample code to create transaction and sample output. I want to do slightly different thing - I want to name top-level element name of mappable object based on one property of that object. Could you please take a look.

[bdoughan]

I've started a new answer to this question based on the updates: stackoverflow.com/questions/4441692/…. I don't want to delete this example as I believe it has value to the community.

[Vladimir]

Thanks so much! Looks like that it does it now. I will check in my project and return with my results!