Creating Lightweight Java Components

This topic describes how you can create lightweight Java components and add them to HTML topics using the HTML <OBJECT> tag. The last section in this topic contains references to supplemental information about lightweight components and the HTML <OBJECT> tag.

References to supplemental information are included at the end of this topic.

Lightweight Components for HTML Topics

Components intended for HTML topic pages are very similar to generic lightweight components. Components that do not require information about the View, or have parameters that can be set, can be used without modification.

View Information

Lightweight components that require information about the View must implement javax/javahelp/impl/ViewAwareComponent. These components implement the method setViewData(). The component can determine information from the View about the environment in which it is executing. For example, in the code snippet below the Document object is derived from the View:

    private View myView;
    static private URL base;

    public void setViewData(View v) {
        myView = v;
        Document d = myView.getDocument();
        // System.err.println("myDocument is: "+d);

        base = ((HTMLDocument) d).getBase();
        // System.err.println(" base is: "+base);

    }

    http://java.sun.com/j2se/1.4.1/docs/api/javax/swing/text/Document.html

    AttributeSet as = v.getAttributes();

    Color color=StyleContants.getBackground(as)

    http://java.sun.com/j2se/1.4.1/docs/api/javax/swing/text/StyleConstants.html

Using Parameters

If your component takes parameters, you should follow these two additional steps:

1. Add accessor methods for each parameter that can be set.
2. Create a BeanInfo class that corresponds to the lightweight component class.

Accessor Methods

Add accessor methods that enable the component to access the parameters through the Java reflection mechanism. In the following example, the AButton class has implemented accessor methods for the parameter "data" in the methods getData and setData:

    private String data = "";

    public void setData(String s) {
	data = s;
    }

    public String getData() {
	return data;
    }

Even if the internal representation is not a String, both the returned value for the getter method and the parameter in the setter method must be a String.

BeanInfo Class

Create a BeanInfo class that provides explicit information about the lightweight component. The only method used by the ContentViewer from the BeanInfo classes is getPropertyDescriptors. In the complete example below, JHSecondaryViewerBeanInfo defines the property data accessible through the getData() and setData() methods in JHSecondaryViewer:

public class JHSecondaryViewerBeanInfo extends SimpleBeanInfo {

   public JHSecondaryViewerBeanInfo() {
   }
    
   public PropertyDescriptor[] getPropertyDescriptors() {
      PropertyDescriptor back[] = new PropertyDescriptor[15];
      try {
         back[0] = new PropertyDescriptor("content", JHSecondaryViewer.class);
         back[1] = new PropertyDescriptor("id", JHSecondaryViewer.class);
         back[2] = new PropertyDescriptor("viewerName", JHSecondaryViewer.class);
         back[3] = new PropertyDescriptor("viewerActivator", JHSecondaryViewer.class);
         back[4] = new PropertyDescriptor("viewerStyle", JHSecondaryViewer.class);
         back[5] = new PropertyDescriptor("viewerLocation", JHSecondaryViewer.class);
         back[6] = new PropertyDescriptor("viewerSize", JHSecondaryViewer.class);
         back[7] = new PropertyDescriptor("iconByName", JHSecondaryViewer.class);
         back[8] = new PropertyDescriptor("iconByID", JHSecondaryViewer.class);
         back[9] = new PropertyDescriptor("text", JHSecondaryViewer.class);
         back[10] = new PropertyDescriptor("textFontFamily", JHSecondaryViewer.class);
         back[11] = new PropertyDescriptor("textFontSize", JHSecondaryViewer.class);
         back[12] = new PropertyDescriptor("textFontWeight", JHSecondaryViewer.class);
         back[13] = new PropertyDescriptor("textFontStyle", JHSecondaryViewer.class);
         back[14] = new PropertyDescriptor("textColor", JHSecondaryViewer.class);
         return back;
      } catch (Exception ex) {
	 return null;
      }
   }
   }

Parameter Names

When naming parameters, be sure to avoid names reserved in the HTML 4.0 specification for use as <OBJECT> tag attributes. For a complete list of <OBJECT> attributes see the HTML 4.0 specification:

    http://w3c.org/TR/REC-html40/

Using the <OBJECT> Tag

You add lightweight components to JavaHelp topics by means of the <OBJECT> tag and its classid attribute. The help viewer only recognizes classid values prefixed with the "java:" tag. All other classid tags are ignored. The following example creates an ALabel within the HTML topic:

    <OBJECT CLASSID="java:sunw.demo.object.ALabel"</OBJECT>

    <OBJECT 
        CLASSID="java:sunw.demo.object.ALabel" 
        width="400" height="500">
    </OBJECT>

Parameters are passed to lightweight components by using the <param> tag. A parameter is only recognized if the component has getter and setter methods for that parameter. A getter or setter method must operate on a String. In the example below, the help viewer passes a number of parameters and their values to a the JHSecondaryViewer component:

    <OBJECT classid="java:com.sun.java.help.impl.JHSecondaryViewer">
        <param name="content" value="../topicB/glossary_def.html">
        <param name="viewerActivator" value="javax.help.LinkLabel">
        <param name="viewerStyle" value="javax.help.Popup">
        <param name="viewerSize" value="300,400">
        <param name="text" value="Click here">
        <param name="textFontFamily" value="SansSerif">
        <param name="textFontSize" value="x-large">
        <param name="textFontWeight" value="plain">
        <param name="textFontStyle" value="italic">
        <param name="textColor" value="red">
    </OBJECT>

Supplemental Information

The following information supplements the information in this topic.

Lightweight Java Components

For general information about lightweight Java components see:

http://java.sun.com/j2se/1.4.1/docs/guide/awt/demos/lightweight/index.html

As a reference, the sources to the lightweight components that implement JavaHelp system popups and secondary windows (JHSecondaryViewer.java and JHSecondaryViewerBeanInfo.java) can be found in src.jar at:

com\sun\java\javahelp\impl

HTML 4.0 Specification

You can find a detailed description of the <OBJECT> tag as part of the HTML 4.0 specification:

http://w3c.org/TR/REC-html40/