Serializing Java objects to XML with WOX

Introduction

This article explains how to use Web Objects in XML (WOX) to serialize Java objects to XML. Although WOX is also a serializer for C# objects, this article only concerns the serialization of Java objects. WOX is available at the WOX Serializer website.

WOX Main Features

Some of the WOX main features are listed below.

• Easy to use. The Easy class provides serialization and de-serialization methods.
• Simple XML. The XML generated is simple, easy to understand, and language independent.
• Requires no class modifications. Classes do not require to have default constructors, getters, or setters.
• Field visibility. Private fields are serialized just as any other field. WOX serializes fields regardless of their visibility.
• Interoperability between Java and C#. WOX can serialize a Java object to XML, and reconstruct the XML back to a C# object; and vice versa.
• Standard XML object representation. This could potentially allow to have WOX serializers in different object-oriented programming languages.
• WOX data types. The WOX mapping table specifies how primitive data types are mapped to WOX data types.
• Robust to class changes. Defaults will be used for newly added fields.
• Arrays. Handles arrays and multi-dimensional arrays of primitives and objects.
• Base-64. Byte arrays are base-64 encoded for efficiency.
• Collection classes. Lists and Maps are provided as WOX data types. (ArrayList and HashMap in Java; ArrayList and Hashtable in C#.)
• Object references. Handles duplicate and circular object references with id/idref.
• Class and Type. Objects of these classes are saved by their string name.
• Small footprint. The woxSerializer.jar file (which contains only .class files) is only 25K.

Using WOX

This is a quick introduction to the WOX serializer in Java. We will first create two classes. Then we will create some objects of those classes which will be serialized to XML. Next, we will have a look at the standard XML generated by WOX, and finally we will see how the XML goes back to a Java object.

public class Student {
    private String name;
    private int registrationNumber;
    private Course[] courses;
    //constructors and methods omitted
}

public class Course {
    private int code;
    private String name;
    private int term;
    //constructors and methods omitted
}

Please notice that the fields in both classes are private. WOX does not take into consideration the visibility of the fields - they will be serialized regardless of their visibility. WOX in Java does not require that classes have default constructors, setters, or getters.

Serializing the Student Object to XML

We first create a student with some courses:

Course[] courses = { new Course(6756, "XML and Related Technologies", 2),
                     new Course(9865, "Object Oriented Programming", 2),
                     new Course(1134, "E-Commerce Programming", 3) };
Student student = new Student ("Carlos Jaimez", 76453, courses);

We now use WOX to serialize the student to XML. We need to specify the file name where the student object will be stored.

String filename = "student.xml";
Easy.save(student, filename);

The save method of the Easy class allows you to serialize an object to XML and store it to the specified XML file.

The resulting XML is shown below:

<object type="Student" id="0">
   <field name="name" type="string" value="Carlos Jaimez" />
   <field name="registrationNumber" type="int" value="76453" />
   <field name="courses">
      <object type="array" elementType="Course" length="3" id="1">
         <object type="Course" id="2">
            <field name="code" type="int" value="6756" />
            <field name="name" type="string" value="XML and Related Technologies" />
            <field name="term" type="int" value="2" />
         </object>
         <object type="Course" id="3">
            <field name="code" type="int" value="9865" />
            <field name="name" type="string" value="Object Oriented Programming" />
            <field name="term" type="int" value="2" />
         </object>
         <object type="Course" id="4">
            <field name="code" type="int" value="1134" />
            <field name="name" type="string" value="E-Commerce Programming" />
            <field name="term" type="int" value="3" />
         </object>
      </object>
   </field>
</object>

The XML generated is a standard representation for the Student object. Every field is mapped to a field element, and every object is mapped to an object element. Also notice that the type attribute gives you the WOX data type of every field. The XML generated by WOX is simple, easy to understand, and language independent.

De-serializing the Student Object Back from XML

We will use the load method of the Easy class to de-seralize the Student object.

Student newStudent = (Student)Easy.load(filename);

Done! The Student object has been reconstructed from XML to Java.

Summary

Web Objects in XML is an approach to serialize Java objects to XML, in a simple and robust way. The XML generated by WOX aims to be language independent, and easy to understand.

In this article, we have covered the following:

• Explain WOX main features.
• Create an object to be serialized.
• Serialize an object to XML, by using the method Easy.save(Object obj, String filename).
• De-serialize the object back from XML, by using the method Easy.load(String filename).

The last version of this XML serializer can be found at the WOX serializer website.

History

• Release 1.0 - May 2008.