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How handlers work in Web-accessible home automation

Using Sun Labs' Brazil server as your starting point

By Rinaldo Digiorgio, Colin Stevens and Stephen Uhler, JavaWorld.com, 05/05/00

Developing consistent, reliable Web applications that interface with such different devices as home networks, home automation systems, and realtime telemetry devices can be vastly simplified by treating devices as URLs. The URL programming interface (UPI) effectively provides a set of URLs for a device that is available to any user capable of performing the HTTP protocol. HTTP has become so universal that computer science students are often given the assignment of creating an HTTP stack.

Using the Java language, Sun Microsystems Laboratories developed a technology with which users can deploy very small HTTP stacks, with a core of less than 100 KB. These small servers can be embedded in devices or used for small tactical application servers that are similar to traditional Web servers. Such minimal servers can be used to provide an integrated presentation and service layer for a device. Because these servers can act as Web servers that answer URL requests, universal access to devices from any Internet node can be achieved.

This article demonstrates how HTTP stacks can be used to deploy interfaces to devices, creating an extranet that contains those devices. The technology discussed in this article was developed at Sun Labs, which has built several prototypes for smart cards, realtime weather stations, and home automation systems that provide authenticated access to any device on the Internet capable of supporting a Java runtime environment directly or via a proxy.

One of the benefits of this architecture is that its different components can easily be used with one another. For example, you can use a smart card to authenticate access to your home by having it interact with your home network and/or environmental systems. What if every device in your home had a URL with some amount of functionality behind it? Or, better yet, what if you could script applications using HTML that allowed you to do things like change the energy management or shut down lights, locally or remotely, using the same interface?

Supporting devices with Web applications will add new utility to the Internet, if the technology is implemented securely. Without security, however, remote home automation will never succeed. Java technology is perfect for this type of application because of its security model and small size.

Architectural overview

Let's first examine the Sun Labs Brazil server. Features of Brazil include:

• A simple extension API (called a handler) that uses a delegation-based object model.
• Dynamic loading of application functionality and configurations. The handlers that provide application functionality are resolved and loaded at runtime.
• Mechanisms for composing application modules, encouraging code reuse with well-known design patterns. Information specific to an entire application is in one place, and made available to all of the handlers, simplifying server modification and configuration.

Figure 1. Brazil X10 architecture

Getting started

To use the server as part of your application, you will need to write one or more handlers. A handler is similar to a servlet in Java Web server terminology, but is lighter in weight.

 

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