Persisting Object State in Xml Format

September 25, 2007

Persistence is the process of saving the state of an object permanently to a storage like file or database, and the state of the object can be restored at a later time. In Java terms, Persistence is nothing but Serialization. For example, the following code is used to save the state of an object in a file.

Assuming that there is some class called Flower implementing java.io.Serializable.

public class Flower implements Serializable {
 
	private String name;
	private String colour;
 
	public Flower(){
	}
 
	public Flower(String name, String colour){
		this.name = name;
		this.colour = colour;
	}
 
	public String getColour() {
		return colour;
	}
 
	public void setColour(String colour) {
		this.colour = colour;
	}
 
	public String getName() {
		return name;
	}
 
	public void setName(String name) {
		this.name = name;
	}
 
	public String toString(){
		return "The " + name + " is " + colour + " in colour.";
	}
}

The following code shows how to persist an object of the class Flower.

    ObjectOutputStream output = new ObjectOutputStream(
        new FileOutputStream("flower"));
    output.writeObject(new Flower("Orchid","Purple"));
    output.close();

If we want to re-construct the original object from the file "flower", then the following piece of code will help.

    ObjectInputStream input = new ObjectInputStream(
        new FileInputStream("flower"));
    Flower orchid = (Flower)input.readObject();
    System.out.println(orchid);

If we try to open the file "flower", nothing can be understood from that, since the format of file is binary.

The output of reconstructing the object from file is,

1	The Orchid is Purple in colour.

We have just seen a simple example of persisting an object. Let us now get into our topic of interest , i.e Persisting Object State in Xml Format. The following program shows how to save and restore the state of an object in an appropriate way by using Xml format.

    FileOutputStream fileOutputStream = new FileOutputStream("flower.xml");
    XMLEncoder encoder = new XMLEncoder(fileOutputStream);
    Flower orchid = new Flower("Rose","Red");
    encoder.writeObject(orchid);
    encoder.close();

The above code makes use of java.beans.XMLEncoder to save the object state in Xml Format. Given below is the code to read the xml file content for re-constructing the object.

1
2
3

    XMLDecoder decoder = new XMLDecoder(new FileInputStream("flower.xml"));
    Flower flower = (Flower)decoder.readObject();
    System.out.println(flower);

The output of reconstructing the object from the flower.xml file is,