Defining a dynamic class using the API

You can create new instances of IlpClass dynamically using the Java API.

The easiest way to define a business model from any Java class is to create business classes as instances of IlpDefaultClass and register related class attributes with IlpDefaultAttribute. For more information, see Business model API. The best place to put the IlpClass definition is the IlpObject implementation.

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);      
  }

In this sample code, you have created the IlpClass as an IlpDefaultClass with a specific implementation of the newInstance method. This method is used to create objects read from an XML file. Its implementation depends entirely on the case you have to handle. Note that you do not need to implement the newInstance method if you do not intend to use XML with your IlpClass .

Here the FileObject class uses a File as its identifier with all its content. The IlpClass parameter allows you to subclass IlpClass . The parameter initializeAttributeValues has the same meaning as in the XML format. See Elements in an XML data file . Here you do not use that parameter because there are no default attribute values.

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.

If your Java classes include attributes, you can write an implementation of IlpObject that will act as a wrapper. This wrapper will delegate methods to the underlying Java object to access its attributes. This implementation of IlpObject is described by an IlpClass.

The main methods to implement are the following:

public static IlpClass GetIlpClass —This method should return the corresponding IlpClass . This method tells the class manager how to retrieve the IlpClass corresponding to the Java class. When its getClass method is called with the Java class as its parameter, the class manager loads the Java class from its name ( Class.forName ) and calls the GetIlpClass method that retrieves the IlpClass . This way, your IlpClass is automatically registered with all the class managers that may use it.

Note

If you do not want a given Java class to be considered as a JavaBean™ and cannot add the static method GetIlpClass to that class, you can register an IlpClass that has the same name as the Java class before the class name is queried from the class manager.
public Object getIdentifier —This method must return an identifier. This identifier can be the underlying Java object, an attribute, or another identifier stored in the implementation of IlpObject .
public IlpClass getIlpClass() —This method returns the IlpClass . Usually, you have to store the IlpClass as a Java attribute of your IlpObject implementation to support subclasses. If you do not want to support subclasses, you can return the result of the static GetIlpClass() method.
public Object getAttributeValue (IlpAttribute attribute) —This method returns the value of an attribute. Therefore, it results in a call to a method of the delegate Java object.
public void setAttributeValue (IlpAttribute attribute, Object value) —This method sets the value of an attribute. It is not meant to be supported for all attributes. If supported, it usually results in a call to a method of the delegate Java object.
public Object getAttributeValue (String attributeName) —This method returns the value of an attribute, given the attribute name. Therefore, it results in a call to a method of the delegate Java object.
public void setAttributeValue (String attributeName, Object value) —This method sets the value of an attribute. It is not meant to be supported for all attributes. If supported, it usually results in a call to a method of the delegate Java object.

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Defining the business model with dynamic classes