Defining a Dynamic Class Using the API

Here is an example taken from the FileObject.java file located in the following sample directory:

<installdir>/samples/datasource/explorer2

where <installdir> is the directory where you have installed JViews TGO.

How to Create a Business Class and Register the Related Class Attributes

    public static IlpDefaultAttribute EXISTS =
      new IlpDefaultAttribute("exists",Boolean.class, true);
    public static IlpDefaultAttribute NAME =
      new IlpDefaultAttribute("name",String.class, true);
    public static IlpDefaultAttribute PARENT =
      new IlpDefaultAttribute("parent",String.class, true);
    public static IlpDefaultAttribute PATH =
      new IlpDefaultAttribute("path",String.class, true);
    public static IlpDefaultAttribute DIRECTORY =
      new IlpDefaultAttribute("directory",Boolean.class, true);
    public static IlpDefaultAttribute HIDDEN =
      new IlpDefaultAttribute("hidden",Boolean.class, true);
    public static IlpDefaultAttribute LASTMODIFIED =
      new IlpDefaultAttribute("lastModified", Long.class, true); 
    public static IlpDefaultAttribute LASTMODIFIEDDATE =
      new IlpDefaultAttribute("lastModifiedDate", Date.class, true);
    public static IlpDefaultAttribute LENGTH =
      new IlpDefaultAttribute("length", Long.class, true);
    public static IlpDefaultAttribute ROOT =
      new IlpDefaultAttribute("root", Boolean.class, true);
 
    protected static IlpDefaultClass ILPCLASS;
      
    static {
    ILPCLASS = new IlpDefaultClass("FileObject") {
      /**
       * This method is called when objects are loaded from XML.
       */
       public IlpObject newInstance(IlpClass ilpClass, Object identifier,
        boolean initializeAttributeValues) {
          return new FileObject((File)identifier,ilpClass);
       }
    };
    ILPCLASS.addAttribute(EXISTS);
    ILPCLASS.addAttribute(NAME);
    ILPCLASS.addAttribute(PARENT);
    ILPCLASS.addAttribute(PATH);
    ILPCLASS.addAttribute(DIRECTORY);
    ILPCLASS.addAttribute(HIDDEN);
    ILPCLASS.addAttribute(LASTMODIFIED); 
    ILPCLASS.addAttribute(LASTMODIFIEDDATE);
    ILPCLASS.addAttribute(LENGTH);
    ILPCLASS.addAttribute(ROOT);      
  }

The class manager is not aware of this new IlpClass. You have to define a static method called GetIlpClass in your implementation of IlpObject to have that class registered with the class manager automatically.

The main methods to implement are the following:

Extending a Predefined Business Class Using the API

How to Create a Wrapper for a Java Object

public class FileObject implements IlpObject {

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;
    }

  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.

 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
  }