The Java Developers Almanac 1.4

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e10. Serializing an Immutable Bean Property to XML

An immutable property is one where the value is supplied to the constructor rather than through a setter method. By default, immutable properties are not persisted. This example demonstrates how to persist an immutable property called prop.

    // Create an object with an immutable property and set the value
    // of the immutable property in the constructor
    MyClass3 o = new MyClass3(123);
    
    try {
        // Create the encoder
        XMLEncoder encoder = new XMLEncoder(new BufferedOutputStream(
            new FileOutputStream("outfilename.xml")));
    
        // Specify to the encoder, the name of the property that is associated
        // with the constructor's parameter(s)
        String[] propertyNames = new String[]{"prop"};
        encoder.setPersistenceDelegate(MyClass3.class,
            new DefaultPersistenceDelegate(propertyNames);
    
        // Serialize the object into XML
        encoder.writeObject(o);
        encoder.close();
    } catch (FileNotFoundException e) {
    }

    // This class defines an immutable property called prop.
    // The value of the immutable property is initialized
    import java.beans.*;
    public class MyClass3 {
        int prop;
        // The constructor that initializes the immutable property prop
        public MyClass3(int prop) {
            this.prop = prop;
        }
    
        // The immutable property
        public int getProp() {
            return prop;
        }
    }

Here is the XML data:

    <?xml version="1.0" encoding="UTF-8"?>
    <java version="1.4.0" class="java.beans.XMLDecoder">
        <object class="MyClass3">
            <int>123</int>
        </object>
    </java>

Related Examples

e7. Serializing a Bean to XML
e8. Deserializing a Bean from XML
e9. Preventing a Bean Property from Being Serialized to XML

See also: Events

© 2002 Addison-Wesley.