java - How do I marshall multiple objects using JAXB?

Question

I'm trying to marshall multiple objects e.g. Book added into BookLists via setBookslst(). I begin using this JAXBContext setup:

jaxbContext = JAXBContext.newInstance(BookLists.class);

and

 jaxbMarshaller.marshal(lists, result);

I'm given the following runtime exception however:

javax.xml.bind.JAXBException: com.jaxb.example.marshall.Book nor any of its super class is known to this context]

My types are defined as follows.

Book :-

@XmlRootElement(name="book")
public class Book {

     private String title;
     private int year;
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
    public int getYear() {
        return year;
    }
    public void setYear(int year) {
        this.year = year;
    }
}

BookList :-

@XmlRootElement(name="lists")
public class BookLists {
List<Book> bookslst;

public List getBookslst() {
    return bookslst;
}

public void setBookslst(List bookslst) {
    this.bookslst = bookslst;
}

}

Marshall Code:-

Book book;
    BookLists lists=new BookLists();
    List lst=new ArrayList();
    book = new Book();
    book.setTitle("Book title");
    book.setYear(2010);
    lst.add(book);
    book = new Book();
    book.setTitle("Book title1");
    book.setYear(2011);
    lst.add(book);
    lists.setBookslst(lst);
    JAXBContext jaxbContext;
    try {
        jaxbContext = JAXBContext.newInstance(BookLists.class);
        Marshaller jaxbMarshaller = jaxbContext.createMarshaller();
        jaxbMarshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        StringWriter result = new StringWriter();

        jaxbMarshaller.marshal(lists, result);
        String xml = result.toString();
        System.out.println(xml);
    } catch (JAXBException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

I am trying to put @XMLSeeAlso annotations(Ref:- JAXB Exception: Class not known to this context). This annotation is not available in my version.

Answer 1

By default a JAXB (JSR-222) implementation examines the public accessor methods. You could add the Book parameter on the List in your get/set methods.

public List<Book> getBookslst() {
    return bookslst;
}

public void setBookslst(List<Book> bookslst) {
    this.bookslst = bookslst;
}

Alternatively you could specify the type of the property using the @XmlElement annotation:

@XmlElement(type=Book.class)
public List getBookslst() {
    return bookslst;
}

You could also specify that your JAXB implementation introspect the fields instead of the properties:

@XmlRootElement(name="lists")
@XmlAccessorType(XmlAccessType.FIELD)
public class BookLists {
    List<Book> bookslst;
}

---

UPDATE

Is there any alternative way to add List instead of BookList in Marshallar.Marshall?

You could create a generic List wrapper object that leveraged the @XmlAnyElement(lax=true) annotation (see: http://blog.bdoughan.com/2010/08/using-xmlanyelement-to-build-generic.html). Then it cold handle a List of anything annotated with @XmlRootElement.

Lists

package forum12323397;

import java.util.ArrayList;
import java.util.List;

import javax.xml.bind.annotation.*;

@XmlRootElement
public class Lists<VALUE> {

    private List<VALUE> values = new ArrayList<VALUE>();

    @XmlAnyElement(lax=true)
    public List<VALUE> getValues() {
        return values;
    }

}

Demo

package forum12323397;

import javax.xml.bind.*;

public class Demo {

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

        Lists<Book> lists = new Lists<Book>();

        Book book1 = new Book();
        book1.setTitle("A Book");
        book1.setYear(2001);
        lists.getValues().add(book1);

        Book book2 = new Book();
        book2.setTitle("Another Book");
        book2.setYear(2007);
        lists.getValues().add(book2);

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

}

Output

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<lists>
    <book>
        <title>A Book</title>
        <year>2001</year>
    </book>
    <book>
        <title>Another Book</title>
        <year>2007</year>
    </book>
</lists>