XStream

XStream is a library to serialize objects to XML and vice versa. It must not be used as a XML processor.

The way that XStream serializes and de-serializes objects is by using Annotations. This post will show you how to annotate a class and how to serialize it.

First of all let’s introduce the class:

public class Book {
     private String isbn;
     private List author;
     private String title;
     private int pages;
     //class continues...
}

This class models a book. It has the ISBN, a list of authors (it’s only a String per author), the title and the number of pages. The point of XStream is that it uses reflection to serialize and de-serialize the objects.
We want to serialize this book to this XML:

<BOOK>
   <ISBN>978-0-9815316-0-1</ISBN>
   <AUTHOR>Martin Odersky</AUTHOR>
   <AUTHOR>Lex Spoon</AUTHOR>
   <AUTHOR>Bill Venners</AUTHOR>
   <TITLE>Programming in Scala</TITLE>
   <PAGES>736</PAGES>
</BOOK>

The next step is to annotate the class:

package com.wordpress.j2eethoughts;
import com.thoughtworks.xstream.annotations.XStreamAlias;
import java.util.List;

@XStreamAlias("BOOK")
public class Book {
     @XStreamAlias("ISBN")
     private String isbn;
     //no annotations
     private List author;
     @XStreamAlias("TITLE")
     private String title;
     @XStreamAlias("PAGES")
     private int pages;
     //class continues...
}

Note that lists must not be annotated. After this, we need to create the facade of XStream:

package com.wordpress.j2eethoughts;

import java.util.ArrayList;
import java.util.List;
import com.thoughtworks.xstream.XStream;

public class Main {
	public static void main(String[] args) {
		XStream xs = new XStream();
		xs.processAnnotations(Book.class);
		xs.addImplicitCollection(Book.class,
			"authors", "AUTHOR", String.class);
		List authors = new ArrayList();
		authors.add("Martin Odersky");
		authors.add("Lex Spoon");
		authors.add("Bill Venners");
		Book book = new Book("978-0-9815316-0-1",
			authors,"Programming in Scala", 736);
		System.out.println(xs.toXML(book));
	}
}

And that’s all, now you can serialize any Book object. For de-serialization you must call the method xs.fromXML passing a String to the method.