java - XSD for having 2 root elements (1 at a time)

Question

So here is a complex/retarded situation. I am writing an XSD and there happens to be a requirement where i need 2 root elements (1 at any given time)

<xs:element name="booksList">
    <xs:complexType>
         <xs:sequence>
             <xs:element name="book" type="bookType" minOccurs="0" maxOccurs="unbounded"/>
         </xs:sequence> 
    </xs:complexType>   
</xs:element>

and then

<xs:element name="book" type="bookType"></xs:element>

at any given time, either of these element will be used as the root element, so an XML would look like

<bookList>
<book>
<author>XYZ</author>
</book>
</bookList>

or

<book>
<author>XYZ</author>
</book>

Both of these XML will be sent back to the user from 2 different URL's i.e. the list will be sent from localhost/books.xml?author=XYZ and single book will be sent from localhost/book_name.xml

How can i achieve this with one xml ? I tried putting the book definition in the XSD but JAXB2.1 didn't generate any Book class. Is there something which i am missing ?

---

EDIT1: BookType has been generated but BookType doesn't have any root element.

Answer 1

XML SCHEMA

I am writing an XSD and there happens to be a requirement where i need 2 root elements (1 at any given time)

The XML schema below supports having the two root elements booksList and book that you are looking for.

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

    <xs:element name="booksList">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="book" type="bookType" minOccurs="0"
                    maxOccurs="unbounded" />
            </xs:sequence>
        </xs:complexType>
    </xs:element>

    <xs:element name="book" type="bookType"></xs:element>

    <xs:complexType name="bookType">
        <xs:sequence>
            <xs:element name="author" type="xs:string" />
        </xs:sequence>
    </xs:complexType>

</xs:schema>

---

GENERATED MODEL

I tried putting the book definition in the XSD but JAXB2.1 didn't generate any Book class.

Your JAXB (JSR-222) implementation will generate a class for the named complex type bookType, then for the bookElement it will create an @XmlElementDecl annotation on the ObjectFactory class.

BooksList

A class with an @XmlRootElement was generated on this class because it corresponds to a global element with an anonymous complex type.

package forum11620825;

import java.util.*;
import javax.xml.bind.annotation.*;

@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "", propOrder = {"book"})
@XmlRootElement(name = "booksList")
public class BooksList {

    protected List<BookType> book;

    public List<BookType> getBook() {
        if (book == null) {
            book = new ArrayList<BookType>();
        }
        return this.book;
    }

}

BookType

This class was generated to correspond to the named complex types.

package forum11620825;

import javax.xml.bind.annotation.*;

@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "bookType", propOrder = {"author"})
public class BookType {

    @XmlElement(required = true)
    protected String author;

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String value) {
        this.author = value;
    }

}

ObjectFactory

Global elements that correspond to named complex types have @XmlElementDecl annotations generated on the ObjectFactory class. This is necessary since multiple global elements could correspond to named complex types.

package forum11620825;

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 {

    private final static QName _Book_QNAME = new QName("", "book");

    public ObjectFactory() {
    }

    public BooksList createBooksList() {
        return new BooksList();
    }

    public BookType createBookType() {
        return new BookType();
    }

    @XmlElementDecl(namespace = "", name = "book")
    public JAXBElement<BookType> createBook(BookType value) {
        return new JAXBElement<BookType>(_Book_QNAME, BookType.class, null, value);
    }

}

---

XML

Below are the XML documents from your question.

booksList.xml

<booksList>
    <book>
        <author>XYZ</author>
    </book>
</booksList>

book.xml

<book>
    <author>XYZ</author>
</book>

---

DEMO CODE

When you unmarshal a document in which the root element corresponds to an @XmlRootElement annotation you get an instance of the corresponding domain object. If you unmarshal a document in which the root element corresponds to an @XmlElementDecl annotation you get back an instance of JAXBElement that wraps a domain object corresponding to the named complex type.

package forum11620825;

import java.io.File;
import javax.xml.bind.*;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance("forum11620825");
        Unmarshaller unmarshaller = jc.createUnmarshaller();

        File input1 = new File("src/forum11620825/booksList.xml");
        BooksList bookList = (BooksList) unmarshaller.unmarshal(input1);

        File input2 = new File("src/forum11620825/book.xml");
        JAXBElement<BookType> je = (JAXBElement<BookType>) unmarshaller.unmarshal(input2);
        BookType bookType = je.getValue();
    }

}

---

UPDATE

Below is a code fragment demonstrating how to wrap an instance of BookType in a JAXBElement so that it can be marshalled.

ObjectFactory objectFactory = new ObjectFactory();
JAXBElement<BookType> jaxbElement = objectFactory.createBook(aBookType);
marshaller.marshal(jaxbElement, System.out);