Extending a predefined business class using the API

The wrapper class FileObject implements the IlpObject interface directly. You could have built it by extending the IlpDefaultObject class, or by using the IlpAttributeValueHolderSupport. However, both these classes contain the structure to store an arbitrary number of attributes and thus have a footprint. In this example, since the underlying File instance stores all the attributes, there is no need for such a structure.

How to create a wrapper for a Java object

public class FileObject implements IlpObject {

The FileObject class contains the definition of the corresponding IlpClass. The corresponding code is not repeated here.

This class contains a number of attribute members. It wraps a java.io.File and has a file attribute, which is also used as the class identifier. This class also contains an IlpClass attribute which makes it possible to use it with IlpClass instances other than the one it defines (typically subclasses of the one it defines). This class also contains an AttributeValueChangeSupport instance that handles notification of attribute changes.

protected File file;
protected IlpClass ilpClass;
protected IlpAttributeValueChangeSupport support = 
   new IlpAttributeValueChangeSupport(this);

The static method GetIlpClass allows you to register the IlpClass with the class manager automatically. Note that ILPCLASS is a static member.

    public static IlpClass GetIlpClass() {
      return ILPCLASS;
    }

The class has two constructors. The first one is the easiest to use, as it takes only the file to be wrapped as parameter. The second one lets you initialize the ilpClass attribute. It corresponds to the method

newInstance(IlpClass ilpClass, Object
								identifier, boolean initializeAttributeValues)

of the IlpClass .

    public FileObject(File file) {
      this.file = file;
      this.ilpClass = GetIlpClass();
    }

    public FileObject(File file, IlpClass ilpClass) {
      this.file = file;
      this.ilpClass = ilpClass;
    }

The following methods add or remove listeners to attribute value changes and fire events. They all delegate to the IlpAttributeValueChangeSupport instance.

  public void addAttributeValueListener (AttributeValueListener l) {
    support.addAttributeValueListener(l);
  }

  public void removeAttributeValueListener (AttributeValueListener l) {
    support.removeAttributeValueListener(l);
  }

  public void fireEvent (AttributeValueEvent ev) {
    support.fireEvent(ev);
  }

The method getAttributeValue retrieves attribute values from the java.io.File object.

public Object getAttributeValue (IlpAttribute attribute) {
    if (attribute == EXISTS) {
      return file.exists()?Boolean.TRUE:Boolean.FALSE;
    }
    if (attribute == NAME) {
      String name = file.getName();
      // for the roots the name may be null, so return the path in this case
      return name != null && name.length() != 0 ?name:file.getPath();
    }
    if (attribute == PARENT) {
      return file.getParent();
    }
    if (attribute == PATH) {
      return file.getPath();
    }
    if (attribute == DIRECTORY) {
      return file.isDirectory()?Boolean.TRUE:Boolean.FALSE;
    }
    if (attribute == HIDDEN) {
      return file.isHidden()?Boolean.TRUE:Boolean.FALSE;
    }
    if (attribute == LASTMODIFIED) {
      return new Long(file.lastModified());
    }
    if (attribute == LASTMODIFIEDDATE) {
      Date date = new Date();
      date.setTime(file.lastModified());
      return date;
    }
    if (attribute == LENGTH) {
      return new Long(file.length());
    }
    if (attribute == ROOT) {
      return file.getParent() == null ?Boolean.TRUE:Boolean.FALSE;
    }
     return null;
  }

Here the method setAttributeValue sets the value for one attribute only and sets off notification about value change.

  public void setAttributeValue (IlpAttribute attribute, Object value) {
    if (attribute == LASTMODIFIED) {
      if (value instanceof Number) {
        file.setLastModified(((Number)value).longValue());
        fireEvent(new AttributeValueEvent(this, LASTMODIFIED));
      } else
        throw new IllegalArgumentException(value+" is not acceptable as value 
of attribute "+attribute);
    }
     }

The getIdentifier method simply returns the wrapped file. The getIlpClass method returns the corresponding attribute. The getIlpAttributeGroup method also returns the IlpClass . The hasAttributeValue method is delegated to the attribute group.

The initializeDefaultValues method does nothing here. It is invoked to initialize the default values of the attributes and corresponds to the XML attribute initializeDefaultValue . See Elements in an XML data file for details.

 public Object getIdentifier() {
    return file;
  }

  public IlpClass getIlpClass() {
    return ilpClass;
  }

  public IlpAttributeGroup getAttributeGroup () {
    return getIlpClass();
  }

  public boolean hasAttributeValue (IlpAttribute a) {
    return getAttributeGroup().hasAttribute(a);
  }

  public void initializeDefaultValues() {
    // nothing to do here
  }

Current section

Defining the business model with dynamic classes