Java Network Programming, 3rd Edition

Chapter 17. Content Handlers

Content handlers are one of the ideas that got developers excited about Java in the first place. At the time that Java was first released, Netscape, NCSA, Spyglass, and a few other combatants were fighting a battle over who would control the standards for web browsing. One of the battlegrounds was different browsers’ ability to handle various kinds of files. The first browsers understood only HTML. The next generation understood HTML and GIF. JPEG support was soon added. The intensity of this battle meant that new versions of browsers were released every couple of weeks. Netscape made the first attempt to break this infinite loop by introducing plug-ins in Navigator 2.0. Plug-ins are platform-dependent browser extenders written in C that add the ability to view new content types such as Adobe PDF and VRML. However, plug-ins have drawbacks. Each new content type requires the user to download and install a new plug-in, if indeed the right plug-in is even available for the user’s platform. To keep up, users had to expend bandwidth and time downloading new browsers and plug-ins, each of which fixed a few bugs and added a few new features.

The Java team saw a way around this dilemma. Their idea was to use Java to download only the parts of the program that had to be updated rather than the entire browser. Furthermore, when the user encountered a web page that used a new content type, the browser could automatically download the code that was needed to view ...