Lobo Clientlets

The Lobo Project

Lobo@SF

Clientlets in Lobo

Clientlets are classes that implement the interface Clientlet as defined in the Clientlet and Extensions API of the Lobo browser.

Clientlets handle web responses and generally render content by producing a Swing or AWT component. They may be thought of as the counterpart of servlets in the client.

Control Flow

A clientlet receives control when its process method is called. An instance of ClientletContext is passed to the method. A clientlet context contains information about the web request and response, as well as various utility methods.

A clientlet must process the web response and do one of the following:

Set a GUI content object by calling setResultingContent.
Redirect to another document by calling navigate or another such method.
Cancel the request by throwing CancelClientletException. This is what is done by the clientlet that triggers downloads in Lobo.

Setup

Currently only extensions (plugins) can set up clientlets in Lobo, by calling addClientletSelector when the extension's init() method is invoked by the browser. A clientlet selector is in charge of creating a Clientlet instance after checking whether a web response is of a type that can be handled by the clientlet in question. This is typically done by invoking the matches() method of the response object.

Sample Code

Lobo implements several clientlets in its primary extension. The following is a simple clientlet that is used by Lobo to render text files.

TextClientlet.java
package org.lobobrowser.primary.clientlets; import org.lobobrowser.clientlet.*; import org.lobobrowser.util.io.IORoutines; import java.io.*; import javax.swing.*; public class TextClientlet implements Clientlet { public TextClientlet() { } public void process(ClientletContext context) throws ClientletException { try { InputStream in = context.getResponse().getInputStream(); try { String text = IORoutines.loadAsText(in, "ISO-8859-1"); JTextArea textArea = new JTextArea(text); textArea.setEditable(false); JScrollPane pane = new JScrollPane(textArea); context.setResultingContent(pane); } finally { in.close(); } } catch(IOException ioe) { throw new ClientletException(ioe); } } }