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Plug into Java with Java Plug-in, Part 2

Use Java Plug-in with the Firefox Web browser

By Jeff Friesen, JavaWorld.com, 06/27/05

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Six years have passed since I wrote "Plug into Java with Java Plug-in" for JavaWorld. My earlier article defined Java Plug-in, showed how to install version 1.2 for Netscape Communicator 4.5 and Internet Explorer 3.02, presented Windows registry settings related to Java Plug-in, explored Java Plug-in's control panel, examined two Java consoles, discussed the <embed> and <object> HTML tags, and revealed a Swing-based demonstration applet.

Many versions of Java and Java Plug-in have emerged since I wrote that article. And since it's showing its age, I've created a sequel that focuses on one of the more recent Java Plug-ins in the context of the Firefox Web browser. This article first shows you how to access Java Plug-in from Firefox. It next examines the Java Plug-in Document Object Model (DOM), applet state persistence, and cookies. Various applets, run from Firefox, reinforce the knowledge you acquire while studying those topics. The article concludes by exploring the link between Firefox and Java Plug-in. Because there is more to Java Plug-in than what I cover in this article, I recommend studying Sun's Java Plug-in documentation to learn more about that technology.

I base this article's material on Mozilla Firefox 1.0, J2SE 5.0, and Windows 98 SE. Even if you don't have this software, I still recommend reading the article. Hopefully, you will discover some interesting material that is new to you.

Java Plug-in and Firefox

Java Plug-in serves as a bridge between a browser and an external Java Runtime Environment (JRE). Java Plug-in is essential for running applets in Firefox because the browser doesn't provide a JRE—including a JVM—of its own. Because this article presents applets that demonstrate different Java Plug-in topics, and because I run these applets in a Firefox context, we should review how to access Java Plug-in from Firefox. For starters, make sure that J2SE 5.0 and JRE are installed on your platform. On my Windows platform, I installed both J2SE and JRE from the jdk-1_5_0-windows-i586.exe installation file. Make sure to include the JRE in the installation because the JRE includes Java Plug-in.

After installing J2SE 5.0, connect Firefox to Java Plug-in: first select Options from Firefox's Tools menu, next select Web Features, and finally check the Enable Java checkbox.

Traditionally, the <embed> and <object> tags had to be specified to run applets under Java Plug-in. This is not necessary with Java Plug-in 5.0, which can run applets specified by the simpler <applet> tag. During installation, you are given the opportunity to have the Internet Explorer and Mozilla (Firefox)/Netscape Web browsers hand off applet execution to Java Plug-in when they encounter the <applet> tag. If you forego this option, you can make the change later via the Java Plug-in control panel. For example, start the control panel and select the Advanced tab. Then click the plus sign to the left of <APPLET> Tag Support and check the box marked Mozilla and Netscape. Close the control panel and Firefox passes execution to Java Plug-in whenever it encounters the <applet> tag. Figure 1 reveals the needed change.